Mucosal Immunity Research Articles

Novel vaccine strategies to induce respiratory mucosal immunity: advances and implications.

Rapid advances in vaccine technology are becoming increasingly important in tackling global health crises caused by respiratory virus infections. While traditional vaccines, primarily administered by intramuscular injection, have proven effective, they often fail to provide the broad upper respiratory tract mucosal immunity, which is urgently needed for first-line control of respiratory viral infections. Furthermore, traditional intramuscular vaccines may not adequately address the immune escape of emerging virus variants. In contrast, respiratory mucosal vaccines developed using the body's mucosal immune response mechanism can simultaneously establish both systemic and mucosal immunity. This dual action effectively allows the respiratory mucosal immune system to function as the first line of defense, preventing infections at the entry points. This review highlights the efficacy of respiratory mucosal vaccines, including innovative delivery methods such as nasal and oral formulations, in enhancing local and systemic immune barriers. Notably, respiratory mucosal vaccines offer potential advantages in protecting against emerging virus variants and maintaining long-term and multidimensional immune memory in the upper respiratory tract. In addition, a combination of intramuscular and respiratory mucosal delivery of vaccines largely improves their coverage and effectiveness, providing valuable insights for future vaccine development and public inoculation strategies.

Effects of dietary supplementation of myristic acid on jejunal mucosa-associated microbiota, mucosal immunity, and growth performance of nursery pigs.

The objective of this study was to investigate the effects of myristic acid on jejunal mucosal microbiota, mucosal immunity, and growth performance of nursery pigs. Thirty-six pigs (6.6 ± 0.4kg of body weight) were assigned to three treatments (n = 12) for 35 d in three phases: (NC) basal diet; (PC) NC + bacitracin; and (MA) NC + myristic acid compound. Pigs were euthanized to collect jejunal mucosa, jejunal tissues, and ileal digesta. The PC increased (p < 0.05) the relative abundance (RA) of Lactobacillus spp., and Bifidobacterium boum than the NC group. The MA increased (p < 0.05) RA of Bifidobacterium dentium and Megasphaera spp. than the NC group. The PC tended to decrease IL-8 (p = 0.053) and protein carbonyl (p = 0.075) whereas IgG (p = 0.051) and IL-8 (p = 0.090) in jejunal mucosa were decreased by the MA. The PC increased (p < 0.05) the villus height to crypt depth ratio than the NC group. Both bacitracin and myristic acid improved the intestinal health and growth performance of nursery pigs. Effects of bacitracin were rather immediate whereas the effects of myristic acid were obtained after a 3-week feeding.

Mucosal immunity elicited by a human-Fcγ receptor-I targeted intranasal vaccine platform enhances resistance against nasopharyngeal colonization of Streptococcus pneumoniae and induces broadly protective immunity against respiratory pathogens.

The development of safe and effective mucosal vaccines are hampered by safety concerns associated with adjuvants or live attenuated microbes. We previously demonstrated that targeting antigens to the human-Fc-gamma-receptor-I (hFcγRI) eliminates the need for adjuvants, thereby mitigating safety concerns associated with the mucosal delivery of adjuvant formulated vaccines. Here we evaluated the role of the route of immunization in the mucosal immunity elicited by the hFcγRI-targeted vaccine approach. To enable Ag targeting, PspA from Streptococcus pneumoniae (Sp) was genetically fused with the hFcγRI-targeting antibody (α-hFcγRI) to generate PspA-FP. Intranasal (IN) immunization with the PspA-FP induced significantly higher IgA, IgG, and memory T cell response in the lung mucosa compared to that of the intramuscular (IM) route, while both routes exhibited similar increase in the systemic IgG response. The IN immunization elicited better resistance against nasal colonization (NC) of Sp compared to the IM immunization. Additionally, the resistance to NC with the IN administered PspA-FP was higher than the PspA-Alum formulation administered by the IM route. While the protection form lethal pulmonary Sp infection correlated with the systemic Ab response, the resistance from NC (of Sp) correlated with the mucosal immune response. Similar to the pneumococcal pneumoniae model, the hFcγRI-targeted vaccine (based on HA as Ag) was equally protective against pulmonary Influenza virus infection via both routes. However, the IN route promoted better protection compared to the IM route against a lethal pulmonary infection with Francisella tularensis (Ft). The enhanced protection against Ft correlated with the superior mucosal immune response elicited by the IN route compared to the IM route. These observations showed a differential requirement for mucosal delivery for protection depending on the type of pathogen. Moreover, this study revealed that the hFcγRI-targeted vaccine platform is broadly-effective as an adjuvant-free mucosal vaccine platform against respiratory pathogens.

Exploring the dynamic responses of group 3 innate lymphoid cells at different times in response to LPS challenge.

Group 3 innate lymphoid cells (ILC3s) have clear roles in regulating mucosal immunity and tissue homeostasis in the intestine, though the immunological functions in lungs remain unclear. This study aimed to demonstrate the dynamic responses of ILC3s to acute inflammation upon LPS challenge. Microarray data and single-cell RNA sequencing (scRNA-seq) data obtained from the GEO database were combined to analyze the function of ILC3 subset, confirmed by flow cytometry assay and qRT-PCR. The gene enrichment analysis of intersected genes identified between microarray data in bacterial pneumonia and single-cell RNA sequencing of intestinal ILC3s were closely related to TNF-alpha effects on cytokine activity, cell motility and apoptosis pathway, indicating the possibility of intestinal ILC3s migration to the lung. Furthermore, the cellular landscapes of ILC3s in lung and intestine at different times after pulmonary infection exhibited varied ILC3 statuses. ILC3s in lung expanded a lot at 48h while intestinal ILC3s decreased at 72h response to LPS challenge, with higher expression of marked genes related to TNF-alpha effects on cytokine activity, cell motility and apoptosis pathway. The main findings in our study may serve as valuable resources for understanding the roles that ILC3s play upon LPS challenge, which may offer opportunities for translating ILC3s as therapeutic targets to regulate LPS-induced pulmonary inflammation.

Lactoferrin exhibits PEDV antiviral activity by interfering with spike-heparan sulfate proteoglycans binding and activating mucosal immune response.

Neonatal piglets infected with Porcine Epidemic Diarrhea Virus (PEDV) experience a mortality rate of up to 90%, resulting in significant economic losses to the swine industry in China. Current strategies using specific antibodies in sow milk to prevent Porcine Epidemic Diarrhea (PED) in these piglets through specific antibodies in sow milk is unsatisfactory. Preliminary studies have shown limited success. Emerging evidence suggests that general immune factors in sow milk provide protection to neonatal piglets, particularly, lactoferrin, play a crucial role in protecting piglets by inhibiting PEDV replication. However, the precise mechanism by which lactoferrin exerts its antiviral effects remains unclear. This study sought to clarify these mechanisms through both in vitro and in vivo approaches, proposing that higher concentrations of lactoferrin lead to greater antiviral activity. It was hypothesized that lactoferrin can impede PEDV by blocking its binding to heparan sulfate proteoglycans (HSPG) on the surface of target cells, and molecular docking experiments was conducted to identify the binding sites between lactoferrin and HSPG. Additionally, the findings indicated that lactoferrin can effectively trigger the maturation of porcine dendritic cells and boosts their antigen-presenting functions, thereby improving intestinal mucosal immunity in neonatal piglets against PEDV. Overall, these findings aid to elucidate the antiviral actions and mechanisms of lactoferrin in sow colostrum, offering new insights for the effective prevention and control of PED in neonatal piglets.

Muco-Penetrating Lipid Nanoparticles Having a Liquid Core for Enhanced Intranasal mRNA Delivery.

Intranasal delivery of mRNA vaccines offers promising opportunities to combat airborne viruses like SARS-CoV-2 by provoking mucosal immunity, which not only defends against respiratory infection but also prevents contagious transmission. However, the development of nasal mRNA vaccines has been hampered by the lack of effective means to overcome the mucus barrier. Herein, ionizable lipid-incorporated liquid lipid nanoparticles (iLLNs) capable of delivering mRNA cargo across airway mucosa are designed. Adjusting the ratios of ionizable and cationic lipids allows fine-tuning of the pKa of iLLNs to the range of nasal mucosal pH (5.5-6.5), thus facilitating mucus penetration via the formation of near-neutral, PEGylated muco-inert surfaces. When nasally administered to mice, the top candidate iLLN-2/mRNA complexes enable about 60-fold greater reporter gene expression in the nasal cavity, compared to the benchmark mRNA-lipid nanoparticles (ALC-LNP) having the same lipid composition as that of BNT162b2 vaccine. Moreover, a prime-boost intranasal immunization of iLLN-2/mRNA complexes elicits a greater magnitude of SARS-CoV-2 spike-specific mucosal IgA and IgG response than ALC-LNP, without triggering any noticeable inflammatory reactions. Taken together, these results provide useful insights for the design of nasally deliverable mRNA formulations for prophylactic applications.

P-2066. Impact of XXB 1.5 Monovalent Booster Vaccination on Mucosal and Systemic Immune Responses in Healthy Adults

Abstract Background The FDA recently approved the first monovalent XBB1.5 booster vaccine. However, the mechanism by which this vaccine stimulates mucosal and systemic immune responses has been understudied.Figure 1.Impact of XBB 1.5 vaccination on viral neutralization titers using pseudo virus assay (left panel) and ACE2 inhibition assay (right panel).Each dot (white) represents a single serum sample tested in parallel with a post-vaccination sample (colored dot) for each of the 28 participants. The mean fold increase in neutralization titers pre- and post-vaccination are shown for Wuhan, XBB 1.5, and BA5 variants. All increases in neutralization titers are significant to P&amp;lt;0.0001 by employing Wilcoxon matched-pairs signed rank test. Methods We examined 28 participants' serum and saliva one week before and two to three weeks after the XBB1.5 mRNA vaccination for neutralizing and binding antibodies to Wuhan and XBB1.5 S protein.Figure 2:Inhibition of ACE2 binding to different S variants by saliva samples pre- and post-vaccination with XBB1.5 monovalent booster.Paired samples represent the percent ACE2 binding inhibition in participants before and after vaccination. Vaccination induced a 1.7-fold increase in ACE2 neutralization in saliva to XBB1.5 (p&amp;lt;0.0001) and 1.2-fold increase in ACE2 neutralization to Wuhan (p=0.03). Significance tested between pre and post-vaccination by Wilcoxon matched-paired sign rank test. *** p&amp;lt;0.001, **** p&amp;lt;0.0001. Results We observed a 2.9 to 2.6-fold and 5.0 to 7.8-fold increase in Wuhan and XBB1.5 serum neutralization titers following mRNA vaccination using pseudovirus and ACE2 neutralization assays respectively, that closely correlated with a rise in binding antibodies to S protein. Vaccination induced a 1.7-fold increase in ACE2 neutralization in saliva to XBB1.5 (p&amp;lt; 0.0001) and 1.2-fold increase in ACE2 neutralization to Wuhan (p=0.03). This increase in neutralization Ab levels in saliva failed to correlate with the number and time of prior COVID-19 infections, vaccination status, type of vaccine, or concomitant rise in S-specific IgA or IgG in saliva or serum. Depletion of IgA or IgG in saliva following vaccination demonstrated that IgA was primarily responsible for the increase in ACE2 blocking activity (mean reduction in blocking activity with IgA depletion=68%, range, 58-81%) compared to IgG (mean reduction=27%, range 0-71%).Figure 3.Role of IgA on percent reduction in ACE2 inhibition in saliva. Depletion of IgA or IgG in saliva following vaccination demonstrated that IgA was primarily responsible for the increase in ACE2 blocking activity (mean reduction in blocking activity with IgA depletion=68%, range, 58-81%) compared to IgG (mean reduction=27%, range 0-71%). Statistical analysis done using unpaired t test. Conclusion The XBB1.5 monovalent vaccine boosts systemic and mucosal viral neutralization antibody levels, primarily to the XBB1.5 variant. Most people have hybrid immunity to SARS-CoV2 now, so mRNA vaccines boost mucosal immune response better than observed earlier in the pandemic. Increased oral mucosal immunity may reduce the risk of COVID-19 progressing to pneumonia and more severe disease. Disclosures All Authors: No reported disclosures

P-1975. Detection of SARS-CoV-2 Specific Secretory IgA and Neutralizing Antibodies in Nasal Secretions of Seronegative Individuals Previously Exposed to COVID-19

Abstract Background Mucosal immunity may contribute to clearing SARS-CoV-2 infection prior to systemic infection. We describe detection of SARS-CoV-2 specific nasal mucosal antibodies in a group of exposed household individuals that evaded systemic infection and remained seronegative.Figure 1.SARS-CoV-2-specific nasal SIgA. SARS-CoV-2-specific nasal SIgA in control and exposed participants (A). Positive thresholds of 0.20 and 6.30 AU/mL were calculated for unadjusted and adjusted SIgA, respectively, based on mean + 3 standard deviation of the control samples. Exposed participants were stratified by the positive threshold and unadjusted (B) SIgA and adjusted (C) SIgA were compared to controls and infected participants. Wilcoxon rank-sum tests determined if medians differed significantly. Methods Between June 2020 and February 2023, nasopharyngeal swabs (NPS) samples and acute and convalescent blood were collected from individuals exposed to a SARS-CoV-2-confirmed household member. Nasal secretory IgA (SIgA) antibodies targeting the SARS-CoV-2 spike protein were measured using a modified ELISA.Figure 2.SARS-CoV-2-specific nasal unadjusted (A) and adjusted (B) SIgA levels at Day 1 (enrollment), Day 8, and Day 15 for exposed seronegative with positive nasal SIgA and infected participants. SARS-CoV-2-specific nasal unadjusted (A) and adjusted (B) SIgA levels at Day 1 (enrollment), Day 8, and Day 15 for exposed seronegative with positive nasal SIgA and infected participants. Wilcoxon signed-rank tests were used to determine if medians (gray) differed significantly. Results Of 36 exposed individuals without SARS-CoV-2 detected by RT-PCR of NPS specimens and seronegative for SARS-CoV-2-specific IgG at acute and convalescent visits, 13 (36.1%) had positive SARS-CoV-2-specific SIgA levels detected in the nasal mucosa. These individuals had significantly higher nasal SIgA (median 0.52 AU/mL) compared with never-exposed, never-infected controls (n=29, 0.001 AU/mL) and infected-family members (n=43, 0.0002 AU/mL) during the acute visit, respectively (both P&amp;lt; 0.001, Figure 1). The nasal SARS-CoV-2-specific SIgA decreased rapidly over two weeks in the exposed seronegative individuals (Day 1 [0.52 AU/mL] vs. Day 8 [0.18 AU/mL] vs. Day 15 [median 0.02 AU/mL], P = 0.001 and 0.13, respectively, Figure 2). In contrast, SIgA increased in infected family members (Day 1 [0.0002 AU/mL] vs. Day 8 [0.65 AU/mL] vs. Day 15 [median 1.14 AU/mL], P &amp;lt; 0.001 and P = 0.09, respectively, Figure 2). Conclusion Transient nasal SARS-CoV-2-specific SIgA detected in exposed, seronegative individuals may have a protective role in preventing systemic infection. Elucidating factors associated with the induction of nasal SIgA response that prevent systemic invasion may inform infection and transmission prevention strategies. Disclosures Pia S. Pannaraj, MD, MPH, AstraZeneca: Grant/Research Support|Pfizer: Grant/Research Support

P-1979. Localized Nasal Mucosal SARS-CoV-2 Antibody Responses and Neutralization Potential based on Exposure History

Abstract Background SARS-CoV-2-specific mucosal antibodies inhibit viral replication and infection within the upper respiratory tract. We investigated nasal secretory IgA (SIgA) induction differences by exposure history and protection against subsequent infection. Visual schematic of exposure groups. Methods Between June 2020 and February 2024, nasopharyngeal swab (NPS) samples were collected 14-89 days following recent infection or vaccination. SARS-CoV-2-specific nasal SIgA adjusted for total IgA (SIgAadj) and nasal neutralization activity were measured using ELISA and a surrogate virus neutralization test kit, respectively. Subsequent infection risk was compared in participants stratified by mucosal antibody levels using a Cox proportional hazards model. Figure 2 SARS-CoV-2 specific nasal secretory IgA adjusted for total IgA (SIgAadj) by exposure group compared using Wilcoxon rank sum tests. Results NPS were collected from participants with SARS-CoV-2 infection only (n=94), vaccination only (n=94), infection then vaccination (n=51), and breakthrough infection (n=94) (Fig 1). Vaccinated individuals received 3 doses of BNT162b2 (n=199, 82.7%) or mRNA-1273 (n=40, 17.3%). The mean age was 28.2 years (range 0.4-75.1), and 197 (59.2%) were female. Individuals with breakthrough infection after vaccination mounted the highest nasal SIgAadj response compared to those with infection-only (median 10.8 vs. 1.3 AU/mL, P &amp;lt; 0.001), vaccination-only (median 0.2 AU/mL, P&amp;lt; 0.001), or prior infection then vaccinated (median 3.2 AU/mL, P = 0.016) (Fig 2). Neutralization activity correlated with nasal SIgAadj (ρ = 0.48, P &amp;lt; 0.001). If vaccination was the most recent exposure, SIgA did not correlate with serum IgG (ρ = 0.08, P = 0.3). Forty new SARS-CoV-2 infections occurred during the 12-month follow-up period (Fig 3). In a multivariable analysis to account for age, gender, and serum IgG, participants with the lowest quartile of nasal SIgAadj levels had 5.8 times higher odds of infection than those with the higher three quartiles of nasal SIgAadj levels within 3 months (P = 0.005) (Table 1). Figure 3 Kaplan-Meier survival curves of time to subsequent SARS-CoV-2 infection in participants stratified by SARS-CoV-2-specific nasal adjusted SIgA upper 75% quantiles (high) vs. lower 25% quartile (low) over 12 months. P = 0.004 for 0-3 months and P = 0.029 for 0-12 months. Conclusion Our data demonstrate the protective role of nasal SIgA in lowering SARS-CoV-2 infection risk. Hybrid immunity induced the most robust mucosal response, suggesting a mucosal vaccine boost following intramuscular priming may help maximize mucosal immunity to prevent infection and community transmission. Predictors of subsequent infection within 0-3, 3-6, and 6-12 months using Cox proportional hazards regression model. Disclosures Pia S. Pannaraj, MD, MPH, AstraZeneca: Grant/Research Support|Pfizer: Grant/Research Support

Food supply toxicants and additives alter the gut microbiota and risk of metabolic disease.

Metabolic disease is rising along with both global industrialization and the use of new commercial, agricultural, and industrial chemicals and food additives. Exposure to these compounds may contribute to aspects of metabolic disease such as obesity, diabetes, and fatty liver disease. Ingesting compounds in the food supply is a key route of human exposure, resulting in the interaction between toxicants or additives and the intestinal microbiota. Toxicants can influence the composition and function of the gut microbiota, and these microbes can metabolize and transform toxicants and food additives. Microbe-toxicant interactions in the intestine can alter host mucosal barrier function, immunity, and metabolism, which may contribute to the risk or severity of metabolic disease development. Targeting the connection between toxicants, food, and immunity in the gut using strategies such as fermentable fiber (i.e., inulin) may mitigate some of the effects of these compounds on host metabolism. Understanding causative factors in the microbe-host relationship that promote toxicant-induced dysmetabolism is an important goal. This review highlights the role of common toxicants (i.e. persistent organic pollutants, pesticides, and fungicides) and food additives (emulsifiers and artificial sweeteners) found in our food supply that alter the gut microbiota and promote metabolic disease development.

A Modular Bacteriophage T4 Nanoparticle Platform Enables Rapid Design of Dual COVID‐19‐Flu Mucosal Vaccines

A multivalent, rapidly deployable, mucosal vaccine platform is desperately needed to prevent acquisition and transmission of respiratory infections during epidemics and pandemics. No such approved platform currently exists and virtually all under investigation use infectious viruses that have safety concerns and are not amenable for multivalent engineering. Herein, a non‐infectious biomaterial platform is presented, the bacteriophage T4 nanoparticle endowed with unique features for modular engineering, which is exploited to design dual COVID‐Flu mucosal vaccines. By leveraging T4's natural affinity to nasal mucosa, in vivo CRISPR engineering, and in vitro SpyCatcher‐SpyTag conjugation, hundreds of antigen molecules are incorporated from SARS‐CoV‐2 and influenza viruses into one nanoparticle. These include spike and hemagglutinin trimers and M2e peptides decorating the capsid while encapsulating matrix or nucleocapsid proteins inside, thereby achieving unprecedented antigen density and diversity, a pinnacle nanoparticle design. Intranasal administration of this adjuvant‐free T4‐CoV‐Flu vaccine induces remarkable mucosal immunity against both respiratory pathogens, including high‐titer neutralizing antibodies and secretory IgA, lung‐resident CD4+/CD8+ T cells, diverse memory B cells, and complete protection against SARS‐CoV‐2 and influenza challenges. Coupled with its scalability in bacterial systems, thermostability, and adjuvant‐ and needle‐free delivery, T4 presents an extraordinary platform to design potent mucosal vaccines against pandemic threats.

State of the Art and Emerging Technologies in Vaccine Design for Respiratory Pathogens.

In this review, we present the efforts made so far in developing effective solutions to prevent infections caused by seven major respiratory pathogens: influenza virus, respiratory syncytial virus (RSV), the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Bordetella pertussis, Streptococcus pneumoniae (pneumococcus), Mycobacterium tuberculosis, and Pseudomonas aeruginosa. Advancements driven by the recent coronavirus disease 2019 (COVID-19) crisis have largely focused on viruses, but effective prophylactic solutions for bacterial pathogens are also needed, especially in light of the antimicrobial resistance (AMR) phenomenon. Here, we discuss various innovative key technologies that can help address this critical need, such as (a) the development of Lung-on-Chip ex vivo models to gain a better understanding of the pathogenesis process and the host-microbe interactions; (b) a more thorough investigation of the mechanisms behind mucosal immunity as the first line of defense against pathogens; (c) the identification of correlates of protection (CoPs) which, in conjunction with the Reverse Vaccinology 2.0 approach, can push a more rational and targeted design of vaccines. By focusing on these critical areas, we expect substantial progress in the development of new vaccines against respiratory bacterial pathogens, thereby enhancing global health protection in the framework of the increasingly concerning AMR emergence.

Dietary Administration of Karonda (Carissa carandas) on the Growth, Digestive Enzymes, Skin Mucosal Immunity, and Pigmentation in Siamese Fighting Fish (Betta splendens)

Karonda (Carissa carandas) fruit contains natural colorants; however, no research has investigated its effects on fish growth and coloration. Thus, this study examined the impacts of C. carandas fruit powder (CCFP) on growth, skin mucosal immunity, digestive enzymes, and pigmentation in Siamese fighting fish (Betta splendens). Flavonoids (15.97 ± 0.48 mg quercetin equivalent/g CCFP), phenolics (43.52 ± 1.73 mg gallic acid equivalent/g CCFP), terpenoids (350.00 ± 15.66 mg linalool equivalent/g CCFP), tannins (40.97 ± 0.15 mg tannic acid equivalent/g CCFP), carotenoids (5.53 ± 0.73 µg/g CCFP), and β-carotene (0.67 ± 0.05 µg/g CCFP) were estimated in CCFP. In the 2,2-diphenyl-1-picrylhydrazyl assay, CCFP showed antioxidant activity with an IC50 of 256.12 ± 7.68 μg/ml. Fish (0.42 ± 0.02 g weight and 3.20 ± 0.07 cm length) were fed diets containing CCFP at 0 (control), 3, 6, and 9 g/kg for 8 weeks. The results showed that CCFP administration significantly enhanced final weight, length, weight gain, specific growth rate, and average daily gain (p &lt; 0.05). No changes in feed conversion ratio, survival, and condition factor were observed (p &gt; 0.05). Dietary CCFP significantly increased skin mucus lysozyme, alkaline phosphatase, IgM, myeloperoxidase, total protein, antioxidant capacity, catalase, and superoxide dismutase. Fish treated with CCFP showed significant increases in intestinal protease, lipase, and amylase activity, as well as skin, muscle, and fin carotenoid levels. In conclusion, the administration of CCFP at 9 g/kg is optimal for improving growth, digestive enzymes, skin mucosal immunity, and pigmentation in B. splendens.

Randomized controlled trial on the efficacy of forest walking compared to urban walking in enhancing mucosal immunity

Scientific research on forest therapy’s preventive medical and mental health effects has advanced, but the need for clear evidence for practical applications remains. We conducted an unblinded randomized controlled trial involving healthy men aged 40–70 to compare the physiological and psychological effects of forest and urban walking. Eighty-four participants were randomly assigned to either the forest or urban group, with 78 completing 90-min walks and analysis. The primary outcome measured was the change in saliva-secreted immunoglobulin A (sIgA) levels. Evaluating researchers were blinded to the groups, but participants and on-site staff were not. Here, we demonstrate a significant increase in saliva-secreted immunoglobulin A (sIgA) levels in the forest group. Furthermore, forest walking resulted in improved mood, including a reduction in stress hormone levels. In conclusion, mindful forest walking has the potential to enhance immunity and promote health.Clinical trial registration: University Hospital Medical Information Network. Trail registration number: UMIN000045851. Approval date: 25/10/2021.

DOP030 Mucosal deficiency of mitochondria-driven humoral immunity is linked to Crohn’s Disease

Abstract Background Secretory IgA (sIgA) is critical for the maintenance of the mucosal barrier function, preventing bacterial translocation and reducing the risk of chronic inflammation. Several decades of research have revealed a dysregulation of the B-cell compartment in inflammatory bowel disease (IBD) of yet unknown origin1,2. While increased serum levels of (auto)antibodies against S. cerevisiae or the intestinal M-cell expressed FimH receptor glycoprotein 2 (GP2) are observed in patients with Crohn’s disease (CD)3, some studies indicated an impaired generation of intestinal immunoglobulin-secreting plasma cells (PCs)4. To unravel the role of mucosal humoral immunity in CD pathogenesis, we aimed to provide an in-depth characterisation of colonic PC differentiation in patients with CD. Methods In-depth phenotyping of patients with CD in remission and non-IBD controls (hospitalised normals) was performed using multi-omics analyses (spatial single-cell proteomics, proteomics, metabolomics, and transcriptomics) of plasma or colon biopsy samples. Colonic switched memory B cells (sMBCs) were sorted from lamina propria mononuclear cells (LPMNCs) by magnetic-activated cell sorting and ex vivo differentiated into PCs. The impact of mitochondrial function on colonic PC maturation was studied in mitochondrial respiratory chain complex V-deficient ATP8 mutant mice and mice that underwent nutritional intervention. Results Despite a hyperactive colonic B-cell compartment, patients with CD displayed significantly diminished mucosal dimeric IgA (dIgA) and fecal IgA compared to non-IBD controls. Polymeric immunoglobulin receptor (PIGR) expression did not differ, excluding a defective epithelial transcytosis of dIgA. Spatial single-cell proteomics uncovered that colonic plasmablasts and immature CD19+CD45+ PCs were increased at the expense of the fully mature CD19-CD45- phenotype. Consistently, PCs generated ex vivo from CD-derived sMBCs revealed impaired capacity to differentiate into IgA-secreting PCs. Metabolic phenotyping indicated a colonic mitochondrial dysfunction in patients with CD that was also reflected in colonic PCs by increased expression of the cell-surface NADase CD38 in concert with decreased expression of mitochondrially encoded transcripts. Of note, splenic PCs isolated from ATP8 mutant mice displayed a hyperproliferative and low-differentiated phenotype, while colonic IgA-secreting PCs were reduced. Conversely, feeding mice an isocaloric glucose-free, high-protein diet, which promotes mitochondrial activity, increased colonic IgA levels. Conclusion In summary, this study links mitochondrial dysfunction to impaired PC differentiation in patients with CD, resulting in reduced levels of sIgA and thereby compromised mucosal barrier integrity.

The gut microbiome, immune modulation, and cognitive decline: insights on the gut-brain axis

The gut microbiome has emerged as a pivotal area of research due to its significant influence on the immune system and cognitive functions. Cognitive disorders, including dementia and Parkinson’s disease, represent substantial global health challenges. This review explores the relationship between gut microbiota, immune modulation, and cognitive decline, with a particular focus on the gut-brain axis. Research indicates that gut bacteria produce metabolites, including short-chain fatty acids (SCFAs), which affect mucosal immunity, antigen presentation, and immune responses, thereby influencing cognitive functions. A noteworthy correlation has been identified between imbalances in the gut microbiome and cognitive impairments, suggesting novel pathways for the treatment of cognitive disorders. Additionally, factors such as diet, environment, and pharmaceuticals play a role in shaping the composition of the gut microbiome, subsequently impacting both immune and cognitive health. This article aims to clarify the complex interactions among gut microbiota, immune regulation, and cognitive disorders, evaluating their potential as therapeutic targets. The goal is to promote microbiome-based treatments and lay the groundwork for future research in this field.

P1039 An Evaluation of Anti-IL23 Therapy in Primary Sclerosing Cholangitis Associated Inflammatory Bowel Disease

Abstract Background The majority of patients with primary sclerosing cholangitis (PSC) have inflammatory bowel disease (IBD). This association has fostered several pathogenic hypotheses linking mucosal immunity to hepatobiliary inflammation. A putative therapeutic target along this axis centres on gut-derived IL-17 secretor cell subtypes, which are activated by interleukin (IL)23. Notably, emergent forms of IBD treatment host several anti-IL23 agents, however safety and efficacy data in PSC patients is limited. Methods We conducted a multi-centre study, evaluating treatment experiences with Ustekinumab (a dual anti-IL12/23 agent), Risankizumab, and Mirikizumab (anti-IL23 alone). Data was analysed to determine treatment impact on liver biochemistry; IBD response defined by serial Mayo colitis scores or faecal calprotectin (FCP) values; and treatment-emergent adverse events. Results Data was accrued across eight centres from 66 pts (Ustekinumab, 62; Risankizumab, 4 [n=1 escalated from Ustekinumab] and Mirikizumab, 1) with median treatment time of 9 months (IQR 5-24). The majority of patients were men (63%; n=42) with a median age at PSC diagnosis of 24y (IQR 17-36). The predominant PSC phenotype was large duct (73%; n=49), with two patients having cirrhosis, 13% (n=7) being transplant recipients, and 66% (n=44) having an IBD phenotype consistent with ulcerative colitis. At baseline, the median FCP and Mayo colitis scores were 810ug/L (IQR 369-1727; n=33/66) and 5 (IQR3-8; n=31/66), respectively. 60 patients were commenced on these agents as 2nd-4th line, after failure of prior biologic therapy. In all, IBD response was observed in 15% (n=8/52) at 6 months, 20% (n=7/35) at 12 months and 21% (n=4/19) at 24 months. Remission was achieved in 3 pts (4.5%) at 18 months. Among non-transplant patients, the median change in ALP from baseline to 6 months was not significant (ALP x upper limit of normal [ULN] 1.4 vs. 1.2; p=0.67), nor from baseline to 12 (ULN 1.1 vs. 1.1; p=0.161) or 24 months (ULN 1.6 vs. 1.0; p=0.074) (Figure 1). No significant differences in serum ALT or bilirubin were observed from baseline to 6, 12 or 24 months. Treatment was discontinued in 37% (n=25/67) due to lack of efficacy and in one patient due to an adverse event. Conclusion Anti-IL23 agents are safe and well-tolerated in PSC-IBD. However, IBD response and remission rates appear to dwarf those seen in IBD alone, with no significant effects on liver biochemistry.

P0627 Pharmacokinetics, Pharmacodynamics, Safety, and Efficacy of Oral Resolvin E1-based Therapy in Inflammatory Bowel Disease (IBD): Translating Resolvin E1 Activation of BLT1 in Experimental Models to Healthy Volunteers

Abstract Background Resolvin E1 (RvE1), an endogenous lipid mediator, shows efficacy in murine colitis models by modulating mucosal immunity and protecting epithelial barrier function. RvE1 and leukotriene B4 (LTB4) are both BLT1 receptor agonists but elicit distinct biological outcomes through biased agonism. LTB4, a pro-inflammatory lipid mediator, initiates and regulates inflammatory responses by stimulating recruitment and activation of immune cells. In contrast, RvE1 selectively engages BLT1 to promote immune homeostasis and repair. TP-317, a stabilized RvE1 molecule, is being investigated as oral therapy for inflammatory bowel disease (IBD). In a sub-chronic murine model of DSS colitis, oral TP-317 (4.0 mg/kg) significantly improved disease activity and histological scores for mucosal inflammation and crypt loss. GLP toxicology studies in rats and dogs support TP-317’s safety profile, with the highest RvE1 doses tested in both preclinical species determined to be the no observed adverse event levels (NOAEL). This Phase 1a clinical study describes the pharmacokinetics (PK), pharmacodynamics (PD) and safety profile of TP-317 given as an enteric-coated tablet to healthy volunteers. Methods Twenty-four subjects were randomized 3:1 to single oral doses of TP-317 at 10, 40 and 80 mg (n=8/group). Safety, tolerability and PK/PD were assessed using standard methods. Subjects receiving the 80 mg dose underwent frequent CBC testing to assess short-term fluctuations in circulating neutrophils. Results Oral TP-317 was well tolerated, producing peak plasma RvE1 concentrations exceeding the EC50 for BLT1 activation (~10 nM) by 1.2, 2.8, and 6.7 times at 10, 40, and 80 mg doses, respectively. The mean AUC of the 80 mg group met regulatory requirements when compared to NOAEL dose exposures in rats and dogs. All 80 mg subjects experienced transient neutropenia, with neutrophils dropping below 1500/mL near RvE1 peak, followed by complete recovery above normal within ~2 hours. A similar pattern was previously observed without safety concerns in healthy subjects receiving an RvE1 drug at 150 mg twice daily for 10 days. Conclusion TP-317 demonstrates good tolerability and achieves adequate systemic RvE1 levels to engage the BLT1 receptor, offering a novel agonist approach to the LTB4-BLT1 pathway. Transient neutropenia observed with TP-317, a known effect of BLT1 activation by LTB4 and RvE1, suggests target engagement in humans. Oral TP-317’s safety profile and unique pro-resolution, barrier-protective mechanism warrant further clinical studies in IBD patients.

Mechanobiological Approach for Intestinal Mucosal Immunology

The intestinal area is composed of diverse cell types that harmonize gut homeostasis, which is influenced by both endogenous and exogenous factors. Notably, the environment of the intestine is exposed to several types of mechanical forces, including shear stress generated by fluid flow, compression and stretch generated by luminal contents and peristaltic waves of the intestine, and stiffness attributed to the extracellular matrix. These forces play critical roles in the regulation of cell proliferation, differentiation, and migration. Many efforts have been made to simulate the actual intestinal environment in vitro. The three-dimensional organoid culture system has emerged as a powerful tool for studying the mechanism of the intestinal epithelial barrier, mimicking rapidly renewing epithelium from intestinal stem cells (ISCs) in vivo. However, many aspects of how mechanical forces, such as shear stress, stiffness, compression, and stretch forces, influence the intestinal area remain unresolved. Here, we review the recent studies elucidating the impact of mechanical forces on intestinal immunity, interaction with the gut microbiome, and intestinal diseases.

Investigating the potential immunomodulatory effects of commercial oral probiotic supplements on equine gastrointestinal tract barrier function

BackgroundOral probiotic dietary supplements are widely used in veterinary medicine, including in horses. It is hypothesized that the presence of probiotic strains can both modulate the intestinal microbiota and affect mucosal immunity parameters. Such a study has not yet been conducted in horses.MethodsThis study involved 12 healthy horses, which were randomly divided into a control group and a group that received a commercial oral probiotic formula containing Lactobacillus rhamnosus, Pedioccus acidilactici or Enterococcus faecium for 84 days. Fecal samples were collected from all horses on day 0 (D0), 28 days after starting the probiotic (D28), 56 days (D56), 84 days (D84) and 28 days after stopping the probiotic (DX) treatment. The samples were subjected to microbiome analysis via next-generation sequencing of hypervariable regions V3-V4 and V7-V9 of the 16S rRNA gene for analysis of short-chain fatty acids via HPLC analysis and fecal secretory immunoglobulin A (SIgA) quantification via ELISA.ResultsMicrobiome analysis revealed no significant differences in either alpha or beta diversity parameters between the groups. No probiotic strains were detected in the samples. Significant changes were detected in three taxa: the family Bacteroidales RF16 group, the genus Erysipelotrichaceae UCG-004, and the genus Fibrobacter during the study in both groups. In all the cases, there was a gradual decrease in relative abundance over time. The concentrations of SCFAs, specifically acetic and propionic acids, significantly increased over time in both groups according to the generalized linear mixed effects (GLME) model. There were no significant differences in fecal SIgA secretion.ConclusionThe present study revealed no effect of the use of a commercial probiotic dietary supplement on either mucosal immunity or the composition of the intestinal microbiota.