Immune Rabbit Serum Research Articles

Immunodominant extracellular loops of Treponema pallidum FadL outer membrane proteins elicit antibodies with opsonic and growth-inhibitory activities.

The global resurgence of syphilis has created a potent stimulus for vaccine development. To identify potentially protective antibodies (Abs) against Treponema pallidum (TPA), we used Pyrococcus furiosus thioredoxin (PfTrx) to display extracellular loops (ECLs) from three TPA outer membrane protein families (outer membrane factors for efflux pumps, eight-stranded β-barrels, and FadLs) to assess their reactivity with immune rabbit serum (IRS). Five ECLs from the FadL orthologs TP0856, TP0858 and TP0865 were immunodominant. Rabbits and mice immunized with these five PfTrx constructs produced ECL-specific Abs that promoted opsonophagocytosis of TPA by rabbit peritoneal and murine bone marrow-derived macrophages at levels comparable to IRS and mouse syphilitic serum. ECL-specific rabbit and mouse Abs also impaired viability, motility, and cellular attachment of spirochetes during in vitro cultivation. The results support the use of ECL-based vaccines and suggest that ECL-specific Abs promote spirochete clearance via Fc receptor-independent as well as Fc receptor-dependent mechanisms.

Antigenicity evaluation of synthetic α-(1,3)-linked D, D-heptoglycan of Helicobacter pylori serotype O6 lipopolysaccharide

Helicobacter pylori, a gram‐negative bacterium, is known to be associated with various gastric pathologies including chronic gastritis, peptic ulcers and gastric carcinoma. Despite the emerging issue of bacterial resistance to antibiotic-based combination therapy, there is currently no vaccine available for H. pylori infection in the market. Here, we report the synthesis of α-(1,3)-D,D-heptoglycan with different chain length from the lipopolysaccharide of H. pylori serogroup O6. The [n + 1] iterative glycosylation strategy was used for heptoglycan chain elongation. The trifluoroacetimidate heptoside donor exhibited much higher efficiency than thioglycoside donor during glycosylation. An antigenicity evaluation using glycan microarrays indicated that α-(1,3)-D,D-hepto-disaccharide, pentasaccharide and hexasaccharide showed stronger binding affinity to IgG antibodies of H. pylori O6 LPS immunized rabbit serum or serum of H. pylori infected patients. These findings provide significant structure − activity relationship information for developing carbohydrate-based vaccines against H. pylori containing α-(1,3)-D,D-heptoglycan.

First Report on Leptospira Species Isolated from Patients in Slovenia.

Leptospirosis is an important worldwide zoonosis, and it has also been reported in Slovenia. The cultivation of Leptospira from human material is difficult. Despite that, we successfully isolated 12 human Leptospira strains isolated from patients between 2002 and 2020 and used various methods for the phenotypic and genotypic characterization of the strains, including matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) using our own MALDI-TOF data library, melting temperature analysis of the amplified lfb1 gene, determination of Leptospira serogroups using rabbit immune sera, NotI-RFLP of the whole Leptospira genome, multilocus sequence typing (MLST) of seven housekeeping genes, and whole-genome sequencing (WGS)-based typing. We confirmed the presence of four pathogenic Leptospira species (L. kirschneri, L. interrogans, L. borgpetersenii, and L. santarosai) and three serogroups: Grippotyphosa, Icterohaemorrhagiae, and Sejroe. MALDI-TOF identified three of seven isolates at the species level and four isolates at the genus level. Serovars of 8 of the 10 strains were determined using NotI-RFLP. MLST showed that the clinical isolates belonged to sequence types ST17, ST110, and ST155. WGS confirmed the analysis of Leptospira strains using conventional methods. In addition, WGS provided better taxonomic resolution for isolate DDA 10944/10.

Development and diagnostic evaluation of indirect enzyme linked immunosorbent assay for Epidermophyton floccosum infection in humans

BackgroundEpidermophyton floccosum is an anthrophophilic dermatophyte widely distributed in the tropics and subtropics. It can invade keratinized tissues of humans and cause superficial mycoses called dermatophytosis (ringworm). ObjectiveThe main objective of this study was to develop an in-house indirect enzyme-linked immunosorbent assay (ELISA) and to evaluate its performance for the immunological diagnosis of E. floccosum infection in humans. MethodsAn in-house indirect ELISA was developed using partially purified E. floccosum antigens, pre immunized rabbit serum as negative control, immunized rabbit polyclonal antibodies as positive control, enzyme labeled goat anti rabbit antibodies and goat anti human antibodies. A total of 50 serum samples from E. floccosum infected patients as confirmed by direct microscopy and culture and 30 samples from humans without history of dermatophyte infection that served as controls were used to evaluate the performance of an in-house indirect ELISA developed in this study. Analytical and diagnostic performance characteristics were determined to evaluate its diagnostic value. ResultsThe diagnostic sensitivity, specificity, positive and negative predictive values of E. floccosum indirect ELISA were 90.00 %, 83.33 %, 90.83 %, 83.83 % respectively. The performance of indirect ELISA assay was compared with gold standard diagnostic tests such as KOH hydrolysis test and fungal culture. The correlation coefficients of E. floccosum indirect ELISA with KOH hydrolysis and fungal culture method were 0.612** and 0.826** (P < 0.01) respectively indicating significant correlation between these tests. ConclusionThis revealed the great potentiality of E. floccosum indirect ELISA in early, specific and precise detection of E. floccosum infection in humans.

Metalloporphyrins Reduce Proteinuria in Podocyte Immune Injury: The Role of Metal and Porphyrin Moieties.

Depending on their central metal atom, metalloporphyrins (MPs) can attenuate or exacerbate the severity of immune-mediated kidney injury, and this has been attributed to the induction or inhibition of heme oxygenase (HO) activity, particularly the inducible isoform (HO-1) of this enzyme. The role of central metal or porphyrin moieties in determining the efficacy of MPs to attenuate injury, as well as mechanisms underlying this effect, have not been assessed. Using an antibody-mediated complement-dependent model of injury directed against rat visceral glomerular epithelial cells (podocytes) and two MPs (FePPIX, CoPPIX) that induce both HO-1 expression and HO enzymatic activity in vivo but differ in their chelated metal, we assessed their efficacy in reducing albuminuria. Podocyte injury was induced using rabbit immune serum raised against the rat podocyte antigen, Fx1A, and containing an anti-Fx1A antibody that activates complement at sites of binding. FePPIX or CoPPIX were injected intraperitoneally (5 mg/kg) 24 h before administration of the anti-Fx1A serum and on days 1, 3, 6, and 10 thereafter. Upon completion of urine collection on day 14, the kidney cortex was obtained for histopathology and isolation of glomeruli, from which total protein extracts were obtained. Target proteins were analyzed by capillary-based separation and immunodetection (Western blot analysis). Both MPs had comparable efficacy in reducing albuminuria in males, but the efficacy of CoPPIX was superior in female rats. The metal-free protoporphyrin, PPIX, had minimal or no effect on urine albumin excretion. CoPPIX was also the most potent MP in inducing glomerular HO-1, reducing complement deposition, and preserving the expression of the complement regulatory protein (CRP) CD55 but not that of CD59, the expression of which was reduced by both MPs. These observations demonstrate that the metal moiety of HO-1-inducing MPs plays an important role in reducing proteinuria via mechanisms involving reduced complement deposition and independently of an effect on CRPs.

Coronavirus spike protein-specific antibodies indicate frequent infections and reinfections in infancy and among BNT162b2-vaccinated healthcare workers

The prevalence of seasonal human coronavirus (HCoV) infections in early childhood and adults has not been well analyzed in longitudinal serological studies. Here we analyzed the changes in HCoV (229E, HKU1, NL63, OC43, MERS, and SARS-CoV-2) spike-specific antibody levels in follow-up serum specimens of 140 children at the age of 1, 2, and 3 years, and of 113 healthcare workers vaccinated for Covid-19 with BNT162b2-vaccine. IgG antibody levels against six recombinant HCoV spike subunit 1 (S1) proteins were measured by enzyme immunoassay. We show that by the age of three years the cumulative seropositivity for seasonal HCoVs increased to 38–81% depending on virus type. BNT162b2 vaccinations increased anti-SARS-CoV-2 S1 antibodies, but no increase in seasonal coronavirus antibodies associated with vaccinations. In healthcare workers (HCWs), during a 1-year follow-up, diagnostic antibody rises were seen in 5, 4 and 14% of the cases against 229E, NL63 and OC43 viruses, respectively, correlating well with the circulating HCoVs. In 6% of the HCWs, a diagnostic antibody rise was seen against S1 of HKU1, however, these rises coincided with anti-OC43 S1 antibody rises. Rabbit and guinea pig immune sera against HCoV S1 proteins indicated immunological cross-reactivity within alpha-CoV (229E and NL63) and beta-CoV (HKU1 and OC43) genera.

Effectiveness of Polyclonal Antibody Immunoconjugate Treatment with Propamidine Isethionate for Amoebic Keratitis in Golden Hamsters.

Acanthamoeba griffini is known to cause amoebic keratitis (AK); its main causes are inadequate hygiene when contact lenses are handled and/or its prolonged use at night, as well as the use of contact lenses during underwater activities. The most used treatment for AK is the combination of propamidine isethionate combined with polyhexamethylene biguanide, which disrupts the cytoplasmic membrane, and damages cellular components and respiratory enzymes. We proposed an immunoconjugate treatment obtained from Acanthamoeba immunized rabbit serum combined with propamidine isethionate; the corneas of hamsters inoculated with A. griffini (MYP2004) were treated with the combined, at 1, 2, and 3 weeks. Propamidine isethionate is frequently used for AK treatment, in vivo study we are found IL-1β and IL-10 expression and caspase 3 activity is significantly increased with respect to the group that was inoculated with the amoeba without receiving any treatment, suggesting that it may be an effect of the toxicity of this drug on the corneal tissue. Application of the immunoconjugate showed enhanced amoebicidal and anti-inflammatory activities, with comparison to propamidine isethionate only. The aim of this study is to evaluate the effect of the immunoconjugate of propamidine isethionate and polyclonal antibodies as a treatment of AK in golden hamsters (Mesocricetus auratus).

Longitudinal antigenic and seroepidemiological analyses of parechovirus A1 in Yamagata, Japan.

To investigate the antigenic changes in parechovirus 1 (PeVA1), seroepidemiological analyses were performed against the Harris strain (Harris), isolated in 1956, and PeVA1/Yamagata.JPN/2021-4785, isolated in 2021, using immune sera and 207 and 237 human serum specimens collected in 2021 and 1976, respectively. Although rabbit immune sera showed the highest neutralization antibody (NT-Ab) titers against the immunized viruses at 1:12 800-1:102 400, they were cross-reactive at 1:400-1:800. All 62 Yamagata isolates obtained between 2001 and 2021 (Yamagata strains), belonging to phylogenetic lineage 1B, reacted more strongly (mostly 4-64 times) to antiserum against PeVA1/Yamagata.JPN/2021-4785 than to antiserum against Harris, belonging to phylogenetic lineage 1 A. Human serum specimens obtained in 2021 showed higher NT-Ab titers against PeVA1/Yamagata.JPN/2021-4785, whereas those obtained in 1976 had similar NT-Ab titers against both strains. These findings suggested that Yamagata strains and Harris were antigenically cross-reactive, although there were differences. There are still high NT-Abs titers present against Harris in 2021 in particular, indicating that PeVA1 has been in circulation with high immunity in the population. In conclusion, this study suggested that PeVA1 has been endemically perpetuated with only minor antigenic changes as well as with high immunity over several decades in the community.

Enhanced in vivo anti-tumor efficacy of whole tumor lysate in combination with whole tumor cell-specific polyclonal antibody.

Despite the widespread utilization of cancer vaccines with specified antigens, the use of whole tumor cell lysates in tumor immunotherapy would be a very promising approach that can overcome several significant obstacles in vaccine production. Whole tumor cells provide a broad source of tumor-associated antigens and can activate cytotoxic T lymphocytes and CD4+ T helper cells concurrently. On the other hand, as an effective immunotherapy strategy, recent investigations have shown that the multi-targeting of tumor cells with polyclonal antibodies, which are also more effective than monoclonal antibodies at mediating effector functions for target elimination, might minimize the escape variants. We prepared polyclonal antibodies by immunizing rabbits with the highly invasive 4T1 breast cancer cell line. In vitro investigation indicated that the immunized rabbit serum inhibited cell proliferation and induced apoptosis in target tumor cells. Moreover, in vivo analysis showed enhanced anti-tumor efficacy of whole tumor cell lysate in combination with tumor cell-immunized serum. This combination therapy proved beneficial in significant inhibition of the tumor growth and the established tumor was entirely eradicated in treated mice. Serial intravenous injections of tumor cell immunized rabbit serum significantly inhibited tumor cell proliferation and induced apoptosis in vitro and in vivo in combination with whole tumor lysate. This platform could be a promising method for developing clinical-grade vaccines and open up the possibility of addressing the effectiveness and safety of cancer vaccines.

Stereoselective Synthesis and Immunological Evaluation of Common O‐antigen of P. mirabilisOE and P. vulgarisTG103

Comprehensive SummaryProteus species especially Proteus mirabilis and Proteus vulgaris are zoonotic pathogens which can cause public health disease. Owing to their antibiotic‐resistance, developing vaccines against these pathogens is urgently required. Herein, we describe the first synthesis of the common O‐antigen of Proteus mirabilis OE and Proteus vulgaris TG 103. The repeating unit incorporates two challenging 1,2‐cis‐glycosidic bonds: the 1,2‐cis‐2‐acetamido‐2‐deoxy‐glucosidic bonds were successfully constructed by use of conformation‐restrained 2‐nitroglucal donor under bifunctional organothiourea catalysis; while the 1,2‐cis‐2‐acetamido‐2‐deoxy‐galactosidic bonds were formed by use of di‐tert‐butylsilylidene protected 2‐azidogalactose donors. The synthetic fragments were screened by glycan microarray with immunized rabbit sera against purified LPS from Proteus mirabilis O54. The results revealed that the synthetic common O‐antigens both hexasaccharide 2 and nonasaccharide 3 can strongly bind with the IgG antibodies (Abs) in the sera, which is highly valuable for further immunological investigation in synthetic carbohydrate‐based vaccine development.

PaR1 secreted by the type IX secretion system is a protective antigen of Riemerella anatipestifer.

Riemerella anatipestifer mainly infects domestic ducks, geese, turkeys, and other birds, and causes considerable economic losses to the global duck industry. Previous studies have shown that concentrated cell-free culture filtrates of R. anatipestifer induce highly significant protection against homologous challenge. In this study, 12 immunogenic proteins were identified in the culture supernatant of R. anatipestifer strain Yb2 with immunoproteomic analysis. Of these, three immunogenic proteins, AS87_RS06600 (designated "PaR1" in this study), AS87_RS09020, and AS87_RS09965, which appeared in more than three spots on the western-blotted membrane, were expressed in Escherichia coli and purified. Animal experiments showed that the recombinant PaR1 (rPaR1) protein protected 41.67% of immunized ducklings against challenge with virulent Yb2, whereas rAS87_RS09020 or rAS87_RS09965 did not, and that ducklings immunized once with rPaR1 were 20, 40, and 0% protected from challenge with R. anatipestifer strains WJ4 (serotype 1), Yb2 (serotype 2), and HXb2 (serotype 10), respectively. In addition, rPaR1 immunized rabbit serum showed bactericidal activity against strain Yb2 at a titer of 1:8. These results indicate that rPaR1 of strain Yb2 protects against homologous challenge. Amino acid homology analysis show that PaR1 is a non-serotype-specific protein among different R. anatipestifer serotypes. Furthermore, PaR1 is mainly secreted outside the cell through the T9SS. Overall, our results demonstrate that R. anatipestifer PaR1 is a non-serotype-specific protective protein secreted by the T9SS.

Plasmodium knowlesi Duffy binding protein alpha region II (PkDBPαII) in clinical isolates from Peninsular Malaysia and Malaysian Borneo exhibit different immune responses in animal models

Plasmodium knowlesi utilizes the Duffy binding protein alpha (PkDBPα) to facilitate its invasion into human erythrocytes. PkDBPα region II (PkDBPαII) from Peninsular Malaysia and Malaysian Borneo has been shown to occur as distinct haplotypes, and the predominant haplotypes from these geographical areas demonstrated differences in binding activity to human erythrocytes in erythrocyte binding assays. This study aimed to determine the effects of genetic polymorphisms in PkDBPαII to immune responses in animal models. The recombinant PkDBPαII (~ 45kDa) of Peninsular Malaysia (PkDBPαII-H) and Malaysian Borneo (PkDBPαII-S) were expressed in a bacterial expression system, purified, and used in mice and rabbit immunization. The profile of cytokines IL-1ra, IL-2, IL-6, IL-10, TNF-α, and IFN-γ in immunized mice spleen was determined via ELISA. The titer and IgG subtype distribution of raised antibodies was characterized. Immunized rabbit sera were purified and used to perform an in vitro merozoite invasion inhibition assay. The PkDBPαII-immunized mice sera of both groups showed high antibody titer and a similar IgG subtype distribution pattern: IgG2b > IgG1 > IgG2a > IgG3. The PkDBPαII-H group was shown to have higher IL-1ra (P = 0.141) and IL-6 (P = 0.049) concentrations, with IL-6 levels significantly higher than that of the PkDBPαII-S group (P ≤ 0.05). Merozoite invasion inhibition assay using purified anti-PkDBPαII antibodies showed a significantly higher inhibition rate in the PkDBPαII-H group than the PkDBPαII-S group (P ≤ 0.05). Besides, anti-PkDBPαII-H antibodies were able to exhibit inhibition activity at a lower concentration than anti-PkDBPαII-S antibodies. PkDBPαII was shown to be immunogenic, and the PkDBPαII haplotype from Peninsular Malaysia exhibited higher responses in cytokines IL-1ra and IL-6, antibody IgM level, and merozoite invasion inhibition assay than the Malaysian Borneo haplotype. This suggests that polymorphisms in the PkDBPαII affect the level of immune responses in the host.

The recombinant Erns and truncated E2-based indirect enzyme-linked immunosorbent assays to distinguishably test specific antibodies against classical swine fever virus and bovine viral diarrhea virus

BackgroundClassical swine fever (CSF) virus is the causative agent of an economically important, highly contagious disease of pigs. CSFV is genetically and serologically related to bovine viral diarrhea virus (BVDV). BVDV infection in pigs can mimic CSF clinical signs, which cause difficulty in differentiation. Serological test for detection of virus specific antibodies is a valuable tool for diagnosis and surveillance of CSFV and BVDV infections in animals. The aim of this study was to develop the CSFV Erns and BVDV tE2 -based ELISAs to distinguishably test specific antibodies against CSFV and BVDV.MethodsThe CSFV Erns and truncated E2 (tE2, residues 690–865) of BVDV were expressed in E. coli and purified by Ni–NTA affinity chromatography, respectively. Employing Erns or tE2 protein as diagnostic antigen, indirect ELISAs were developed to distinguishably test specific antibodies against CSFV and BVDV. The specificity and sensitivity of ELISAs were evaluated using a panel of virus specific sera of pigs, immunized rabbits and immunized mice. A total 150 clinical serum samples from farm pigs were measured by the developed ELISAs and compared with virus neutralizing test (VNT).ResultsIndirect ELISA was established based on recombinant CSFV Erns or BVDV tE2 protein, respectively. No serological cross-reaction between antibodies against CSFV and BVDV was observed in sera of immunized rabbits, immunized mice or farm pigs by detections of the Erns and tE2 -based ELISAs. Compared to VNT, the CSFV Erns -based ELISA displayed a high sensitivity (93.3%), specificity (92.0%) and agreement rate (92.7%), and the sensitivity, specificity and agreement rate of BVDV tE2 -based ELISA was 92.3%, 95.2% and 94.7%, respectively.ConclusionThe newly developed ELISAs are highly specific and sensitive and would be valuable tools for serological diagnosis for CSFV and BVDV infections.

Characterization of a Peptide Antibody Specific to the Adenylyl Cyclase-Associated Protein of Acanthamoeba castellanii.

Acanthamoeba keratitis (AK) is a rare infectious disease and accurate diagnosis has remained arduous as clinical manifestations of AK were similar to keratitis of viral, bacterial, or fungal origins. In this study, we described the production of a polyclonal peptide antibody against the adenylyl cyclase-associated protein (ACAP) of A. castellanii, and evaluated its differential diagnostic potential. Enzyme-linked immunosorbent assay revealed high titers of A. castellanii-specific IgG and IgA antibodies being present in low dilutions of immunized rabbit serum. Western blot analysis revealed that the ACAP antibody specifically interacted with A. castellanii, while not interacting with human corneal epithelial (HCE) cells and other causes of keratitis such as Fusarium solani, Pseudomonas aeruginosa, and Staphylococcus aureus. Immunocytochemistry (ICC) results confirmed the specific detection of trophozoites and cysts of A. castellanii co-cultured with HCE cells. The ACAP antibody also specifically interacted with the trophozoites and cysts of 5 other Acanthamoeba species. These results indicate that the ACAP antibody of A. castellanii can specifically detect multiple AK-causing members belonging to the genus Acanthamoeba and may be useful for differentially diagnosing Acanthamoeba infections.

Introducing a new anti-Rhipicephalus (Boophilus) microplus tick recombinant vaccine candidate using cathepsin and tropomyosin multi-epitope gene.

Rhipicephalus (Boophilus) spp. are important vectors for Babesia and Anaplasma species causing severe economic losses in livestock. Chemical compounds are commonly used to control tick infestation; however, acaricides resistance in tick has led to move toward alternative strategies such as vaccination. In this study, we introduced a vaccine candidate, namely CaTro against Rh. microplus tick composing of immunogenic B-cell epitopes derived from Rh. microplus cathepsin L and tropomyosin proteins. To evaluate this vaccine candidate, firstly the CaTro sequence was inserted into the prokaryotic expression vector and the recombinant protein CaTro was expressed in Bl21 bacteria. Afterward, purification was performed by Ni-NTA affinity chromatography. The quality of purified recombinant CaTro was also analyzed using sodium dodecyl sulfate-gel electrophoresis and western blotting. Moreover, to evaluate the induction of immune response, the rabbits were immunized with purified recombinant protein combined with Freund’s adjuvant. The findings of this study revealed molecular weight of expressed protein (CaTro) as 38.00 kDa. Furthermore, anti-CaTro antibody was detected in immunized rabbit's sera through dot blotting; while, there was not any response to the control rabbit's sera. The results suggest that CaTro is a potential candidate to develop an anti- Rh. microplus tick.

Anti-cancer immunoprotective effects of immunization with hydatid cyst wall antigens in a non-immunogenic and metastatic triple-negative murine mammary carcinoma model

Cancer vaccines have gained lots of attention as the future of cancer treatment. However, poor immunogenicity of tumor-associated antigens often fails to induce an efficient immune response against the tumor. Strange anti-tumor immune responses at the parasite-infected patients due to cross-reactivity have been reported in various studies. Therefore, parasite antigens with significant immunogenicity and high epitope homology with cancer antigens may activate a strong immune response against cancer cells. Herein, the sera of immunized rabbits with the hydatid cyst wall (HCW) antigens were incubated with 4 T1 mammary carcinoma cells to investigate cross-reactivity between the HCW antigens antisera and surface antigens of the breast cancer cells. Also, the SDS-PAGE profile of HCW antigens was prepared and incubated with the breast cancer patients’ sera and considerable reactivity was observed between their sera and a specific band (~27/28 kDa) according to Western blotting analyzes. Then, the protein bands with cross-reactivity with breast cancer patients’ sera were utilized for prophylactic immunizations of Balb/c mice. The immunoprotective effect of immunization with the HCW antigens caused significant inhibition of 4 T1 breast tumor growth, decrease of metastasis, and enlargement of the tumor-bearing mice survival time in comparison with PBS and pure immune adjuvant injected groups. Mass spectrometry analysis showed that the ~ 27/28 kDa band has numbers of proteins/polypeptides with a high degree of homology with cancer cells antigens which can be the reason for this cross-reactivity and anti-tumor immune response. Taking together, immunization with HCW antigens would be a promising approach in cancer immunotherapy after further investigations.

Elicitation of potent serum neutralizing antibody responses in rabbits by immunization with an HIV-1 clade C trimeric Env derived from an Indian elite neutralizer.

Evaluating the structure-function relationship of viral envelope (Env) evolution and the development of broadly cross-neutralizing antibodies (bnAbs) in natural infection can inform rational immunogen design. In the present study, we examined the magnitude and specificity of autologous neutralizing antibodies induced in rabbits by a novel HIV-1 clade C Env protein (1PGE-THIVC) vis-à-vis those developed in an elite neutralizer from whom the env sequence was obtained that was used to prepare the soluble Env protein. The novel 1PGE-THIVC Env trimer displayed a native like pre-fusion closed conformation in solution as determined by small angle X-ray scattering (SAXS) and negative stain electron microscopy (EM). This closed spike conformation of 1PGE-THIVC Env trimers was correlated with weak or undetectable binding of non-neutralizing monoclonal antibodies (mAbs) compared to neutralizing mAbs. Furthermore, 1PGE-THIVC SOSIP induced potent neutralizing antibodies in rabbits to autologous virus variants. The autologous neutralizing antibody specificity induced in rabbits by 1PGE-THIVC was mapped to the C3/V4 region (T362/P401) of viral Env. This observation agreed with electron microscopy polyclonal epitope mapping (EMPEM) of the Env trimer complexed with IgG Fab prepared from the immunized rabbit sera. Our study demonstrated neutralization of sequence matched and unmatched autologous viruses by serum antibodies induced in rabbits by 1PGE-THIVC and also highlighted a comparable specificity for the 1PGE-THIVC SOSIP trimer with that seen with polyclonal antibodies elicited in the elite neutralizer by negative-stain electron microscopy polyclonal epitope (ns-EMPEM) mapping.

Evidence that immunization with TP0751, a bipartite Treponema pallidum lipoprotein with an intrinsically disordered region and lipocalin fold, fails to protect in the rabbit model of experimental syphilis.

Deconvolution of syphilis pathogenesis and selection of candidate syphilis vaccinogens requires detailed knowledge of the molecular architecture of the Treponema pallidum outer membrane (OM). The T. pallidum OM contains a low density of integral OM proteins, while the spirochete’s many lipoprotein immunogens are periplasmic. TP0751, a lipoprotein with a lipocalin fold, is reportedly a surface-exposed protease/adhesin and protective antigen. The rapid expansion of calycin/lipocalin structures in the RCSB PDB database prompted a comprehensive reassessment of TP0751. Small angle X-ray scattering analysis of full-length protein revealed a bipartite topology consisting of an N-terminal, intrinsically disordered region (IDR) and the previously characterized C-terminal lipocalin domain. A DALI server query using the lipocalin domain yielded 97 hits, 52 belonging to the calycin superfamily, including 15 bacterial lipocalins, but no Gram-negative surface proteins. Surprisingly, Tpp17 (TP0435) was identified as a structural ortholog of TP0751. In silico docking predicted that TP0751 can bind diverse ligands along the rim of its eight-stranded β-barrel; high affinity binding of one predicted ligand, heme, to the lipocalin domain was demonstrated. qRT-PCR and immunoblotting revealed very low expression of TP0751 compared to other T. pallidum lipoproteins. Immunoblot analysis of immune rabbit serum failed to detect TP0751 antibodies, while only one of five patients with secondary syphilis mounted a discernible TP0751-specific antibody response. In opsonophagocytosis assays, neither TP0751 nor Tpp17 antibodies promoted uptake of T. pallidum by rabbit peritoneal macrophages. Rabbits immunized with intact, full-length TP0751 showed no protection against local or disseminated infection following intradermal challenge with T. pallidum. Our data argue that, like other lipoprotein lipocalins in dual-membrane bacteria, TP0751 is periplasmic and binds small molecules, and we propose that its IDR facilitates ligand binding by and offloading from the lipocalin domain. The inability of TP0751 to elicit opsonic or protective antibodies is consistent with a subsurface location.

Peptidorhamanomannan: A surface fungal glycoconjugate from Scedosporium aurantiacum and Scedosporium minutisporum and its recognition by macrophages.

The genus Scedosporium is composed of clinically relevant fungal species, such as Scedosporium aurantiacum, Scedosporium apiospermum, and Scedosporium boydii. Surface molecules have been described that play crucial roles in fungi-macrophage interaction, and many of them are pathogen-associated molecular patterns (PAMPs). The present study aims to characterize peptidoglycans obtained from Scedosporium aurantiacum and Scedosporium minutisporum, a clinical and an environmental isolate, respectively, and compare their roles in pathogen-host interaction. Both molecules were characterized as peptidorhamnomannans (PRMs), similar to what has been already described for other Scedosporium species. Rabbit immune sera obtained by injecting whole cells from each species recognized both fungal cells and purified PRMs, suggesting that a cross-reaction occur between both fungi. Immunofluorescent microscopy revealed that PRMs are exposed on fungal surface. Prior incubation of purified molecules with immune sera before adding to cells led to loss of fluorescent, indicating that PRM is a major molecule recognized by immune sera. Fungi-macrophage interaction revealed that S. aurantiacum is able to survive more inside phagocytic cells than S. minutisporum, and PRM from both fungi plays a role in phagocytosis when the purified molecule is pre-incubated with macrophage. In addition, PRM induce nitric oxide release by macrophages. Our data indicate that PRM is an important PAMP exposed on fungal surface with the potential of immune modulation.

Peptidorhamnomannan from Lomentospora prolificans modulates the inflammatory response in macrophages infected with Candida albicans

BackgroundPeptidorhamnomannan is a glycoconjugate that consists of a peptide chain substituted by O- and N-linked glycans, present on the cell surface of Lomentospora prolificans, a saprophytic fungus which is widely distributed in regions with temperate climates. O-linked oligosaccharides from peptidorhamnomannan isolated from Lomentospora prolificans conidia are recognized by macrophages mediating macrophage - conidia interaction. In this work, peptidorhamnomannan was isolated from L. prolificans mycelium cell wall and its role in macrophage - Candida albicans interaction was evaluated.ResultsPurified peptidorhamnomannan inhibits the reactivity of rabbit immune sera to mycelial and conidia forms of L. prolificans, indicating that this glycoconjugate is exposed on the fungal surface and can mediate interaction with host immune cells. We demonstrated that peptidorhamnomannan leads to TNF-α production in J774 macrophages for 1, 2 and 3 h of incubation, suggesting that this glycoconjugate may have a beneficial role in the response to fungal infections. In order to confirm this possibility, the effect of peptidorhamnomannan on the macrophage - C. albicans interaction was evaluated. Macrophages treated with peptidorhamnomannan led to a lower fungal survival, suggesting that peptidorhamnomannan induces an increased fungicidal activity in macrophages. Furthermore, TNF-α levels were measured in supernatants after macrophage - C. albicans interaction for 1, 2 and 3 h. Peptidorhamnomannan treatment led to a higher TNF-α production at the beginning of the interaction. However, the release of TNF-α was not maintained after 1 h of incubation. Besides, peptidorhamnomannan did not show any inhibitory or fungicidal effect in C. albicans when used at 100 μg/ml but it was able to kill C. albicans at a concentration of 400 μg/ml.ConclusionWe suggest that peptidorhamnomannan acts as a molecular pattern on the invading pathogen, promotes TNF-α production and, thus, increases macrophage fungicidal activity against Candida albicans.