Germinal Center Responses Research Articles

The mechanism of immune dysregulation caused by porcine reproductive and respiratory syndrome virus (PRRSV)

PRRSV is capable of evading the effective immune response, thus persisting in piglets and throughout the swine herd. We show here that PRRSV invades the thymus and causes depletion of T-cell precursors and alteration of the TCR repertoire. Developing thymocytes are affected during negative selection when they transit from the triple-negative to triple-positive stages at the corticomedullary junction just before entering the medulla. The restriction of repertoire diversification occurs in both helper and cytotoxic αβ-T cells. As a result, critical viral epitopes are tolerated, and infection becomes chronic. However, not all viral epitopes are tolerated. Infected piglets develop antibodies capable of recognizing PRRSV, but these are not virus neutralizing. Further analysis showed that the lack of an effective immune response against the critical viral structures results in the absence of a germinal center response, overactivation of T and B cells in the periphery, robust production of useless antibodies of all isotypes, and the inability to eliminate the virus. Overall, the results show how a respiratory virus that primarily infects and destroys myelomonocytic cells has evolved strategies to disrupt the immune system. These mechanisms may be a prototype for how other viruses can similarly modulate the host immune system.

T Follicular Helper Cells Restrain Obesity-Related Metabolic Disease by Damping Intestinal Inflammation

Abstract The intestinal immune system is a central modulator of obesity-associated metabolic disease. Particularly, high-affinity intestinal IgA maintains gut homeostasis after its generation in a germinal center (GC) response that requires functional T follicular helper (Tfh) cells in Peyer’s patches (PP). The objective of this study was to determine how obesity affects Tfh function leading to metabolic disease. We investigated the phenotype of Tfh cells in diet-induced obese mice. Obese mice showed enlarged PP featured by an expansion of CXCR5 highICOS highTfh cells. Surprisingly, intestinal Tfh cells in obese mice showed evidence of dysfunction as they expressed substantially lower PD1 and BCL6 but higher CCR7. As a result, the GC response and the generation of IgA +B cells are also defective in obese mice. To determine if Tfh directly regulate intestinal inflammation and metabolic disease during obesity, we fed Tfh-deficient (Cd4 CreBcl6 flox) mice a western diet and investigated their microbiota composition, barrier integrity, and inflammatory status. In the gut, Tfh-deficient obese mice showed a disturbed microbiota, reduced regulatory T cells (Tregs), compromised intestinal barrier, and a loss of the microbiota-derived short-chain fatty acid butyrate. Moreover, we observed exacerbated liver inflammation in Tfh-deficient mice, suggesting a fundamental role for Tfh in dampening inflammation in the gut-liver axis. Mechanistically, Tfh cells express lower levels of insulin receptors and increased Foxo1, suggesting that reduced insulin signaling underlies the dysfunction of Tfh cells during obesity. Overall, our findings highlight an unexpected role for Tfh cells as essential regulators of obesity-related metabolic disease.

The proviral role of B cell-intrinsic IL-17RA signaling in the establishment of chronic gammaherpesvirus infection

Abstract Epstein-Barr virus (EBV) is a human specific gammaherpesvirus that establishes lifelong infection in >95% of all adults and is associated with multiple cancers, including B cell lymphomas. Murine gammaherpesvirus 68 (MHV68) is a natural rodent pathogen that is genetically and biologically related to EBV and importantly provides a tractable animal model to study viral and host factors that impact chronic infection. Both of these viruses have a natural tropism for B cells and usurp B cell differentiation to drive a robust polyclonal germinal center response, which is needed to establish the latent viral reservoir in memory B cells. The factors which these viruses use to usurp the host germinal center response to establish chronic infection are not clearly defined. Using MHV68 we discovered that global IL-17RA signaling as well as T-cell intrinsic IL-17RA signaling is proviral and supports the gammaherpesvirus-driven germinal center response needed to establish chronic infection. Loss of global and T-cell intrinsic IL-17RA signaling resulted in a significant attenuation in the germinal center response as well as viral latency and reactivation. Given the B cell tropism of MHV68 we generated a B cell specific model of IL-17RA deficiency to understand the significance of IL-17RA signaling in virally infected cells. Loss of IL-17RA signaling in B cells during MHV68 infection resulted in an attenuated germinal center response as well as reduced viral reactivation and latency, similar to what was observed in the loss of global and T-cell intrinsic IL-17RA signaling. This indicates that IL-17RA signaling in both virally infected and uninfected cells play an important proviral role in the establishment of chronic gammaherpesvirus infection. WMed Start up funds and an American Cancer Society Postdoctoral Award (134165-PF-19-176-01-MPC) which was used to generate the B cell specific IL-17RA deficient mice.

Aging is associated with accumulated T follicular helper cells with decreased metabolic function

Abstract The aging immune system responds poorly to infection and vaccination, producing reduced numbers of germinal centers, low affinity antibody titers, and reduced B cell memory. Prolonged contacts between activated B cells and CD4+ T cells are crucial to germinal center formation and T follicular helper cell (Tfh) differentiation, but it is unclear how aging impacts the quality of this interaction. Peptide immunization confirmed that aged mice have less expansion of antigen-specific germinal center B cells and reduced antibody titers. Furthermore, aging was associated with decreased CD4+ T conventional cells and accumulated Tfh cells and regulatory T cells, even in naïve mice. Despite increased numbers, our results indicate that aged Tfh have decreased metabolic function, which may have repercussions on germinal center responses. To determine the contribution of cell-extrinsic influences on antigen-specific Tfh induction, we adoptively transferred young, antigen-specific B and CD4+ naïve T cells into aged hosts prior to peptide immunization, which resulted in reduced antigen-specific germinal center B cell and Tfh expansion and reduced antibody titers when compared to young hosts. The results from these experiments emphasize the importance of the lymphoid microenvironment in germinal center initiation and maintenance. We hypothesize that age-associated Tfh accumulation may impair antigen-specific Tfh induction and subsequent germinal center responses. Current studies use live-cell 2-photon microscopy to track the impact of age on lymphocyte motility and Tfh:B interactions, in order to determine the relative contributions of aged APCs, non-specific aged Tfh, and aged regulatory T cells to germinal center deficiency. Research supported by the Mayo Clinic Robert and Arlene Kogod Center on Aging Innovation Award UL1R002377

Understanding Mechanisms of Adjuvancy in Muscle by mRNA/Lipid Nanoparticles

Abstract Vaccines utilizing encapsulated mRNA within lipid nanoparticles (LNPs) have demonstrated unprecedented efficacy in clinical studies of mRNA-1273 and BNT162b2, two prominent vaccines developed against the S protein of SARS-CoV-2. Despite several Phase III trials offering deep clinical intuition about vaccine efficacy, the musculo-immune basis for elicitation of a strong germinal center response from mRNA/LNP vaccine remains unclear. Here, we characterize the trajectory of the immune response to an mRNA lipid nanoparticle vaccine, encapsulated in sm-102 (Moderna). Furthermore, we find that intramuscular administration of empty LNPs elicits a strong neutrophil and dendritic response within 24h. Additionally, we show that skeletal muscle may play a role in the early immune response to mRNA LNPs. Inflammatory LNPs thus contribute to the well-established role of RNA immunogenicity. Using a reporter of transduction, we show that both >10% of muscle-resident myeloid and lymphoid cells are directly transduced with mRNA vaccines, and that these cells play a crucial role in the downstream germinal center response. Transcriptomic measurements of muscle tissue reveal a direct role role of ionizable lipid operating as an adjuvant to induce this response. Using in vitro and molecular tools, these studies advance our understanding of the cellular and molecular basis for LNP-mediated inflammation and adjuvancy underpinning the exceptional clinical efficacy of mRNA/LNP vaccination.

Expanded T regulatory cells fail to control germinal center responses in the lung lymph nodes of pulmonary fibrosis patients

Abstract Idiopathic pulmonary fibrosis (IPF) is the most common form of interstitial lung diseases (ILD), which is characterized by progressive scarring of the lung. While immune suppression is a viable therapeutic option for many ILDs, it is detrimental in IPF. Nevertheless, enlargement of lung-draining lymph nodes (LLN) is prevalent and predicts survival outcomes in all ILD patients, including IPF, suggesting that there is also an immune component to IPF pathogenesis. To test this hypothesis, we investigated the cellular composition of the LLN in IPF and non-IPF ILD patients. All ILD patients’ LLN had increased germinal centers (GC), implicating that immune responses are not being resolved. As T regulatory cells (Tregs) are key in the control and resolution of immune responses, we investigated the phenotype of Tregs in the LLN of both IPF and non-IPF ILD patients to reveal their role in lung fibrosis. Tregs were expanded in LLN of all ILD patients compared to controls. Interestingly, there was a predominance of GATA3-expressing Tregs in ILD patients’ LLN. However, Tregs of ILD patients expressed significantly elevated levels of ICOS and CD137 compared to controls, indicating recent activation. Surprisingly, CD25 expression was significantly lower on Tregs from ILD patients’ LLN. Sc-RNAseq confirms similar Treg phenotypes in the lungs of IPF patients. In a mouse model of bleomycin-induced pulmonary fibrosis, Tregs expand and display a similar activated phenotype. Preliminary experiments suggest that GATA3 expression in Tregs is detrimental in this model. Together, these data indicate that there are unresolved GC responses in the LLN of all ILD patients, including IPF, and suggest that Tregs are ineffectual at controlling the GC response. American Heart Association Postdoctoral Fellowship, Award number (835938)

Tunable dynamics of B cell selection in gut germinal centers.

Abstract B lymphocytes are central to maintaining balanced enteric responses through production of immunoglobulins (Igs). A large fraction of Igs are produced in germinal center (GC) responses, which form upon immunization or infection in the majority of secondary lymphoid organs, but are constitutively present in gut-associated lymphoid tissue. However, the ontogeny and antigenic drivers of constitutive gut-associated GCs were poorly understood. Using a multicolor fate-mapping approach with the Confetti fluorescent allele to visualize GC clonal expansions, we observed single-color GCs in the steady state intestine, suggestive of strong selection events. By coupling fate-mapping, gnotobiotics and Ig sequencing, we showed affinity-driven selection occurring in gut-associated GCs in response to members of the microbiome. We observed that these GCs persist even in the absence of microbiota, although their isotype distribution and clonal composition are altered. Furthermore, we identified several prominent public Ig clonotypes in intestinal GCs, whose presence were tuned by microbial diversity.

Kidney disease impairs B cells response against infection via inhibiting germinal center formation and antibody titers

Abstract Immunity to infections is crucial to healthy life. However, recent Covid-19 pandemic has shown that comorbidity such as kidney disease and associated uremia impairs immunity against infections. Uremic patients show high susceptible to infections and also exhibit poor antibody responses to vaccine. The mechanisms by which uremia negatively impacts antibody response is unknown. Using multiple mouse models of uremia, we assessed B cells response to model antigen NP-KLH in alum. We show that uremia inhibits both canonical germinal center (GC) and non-canonical extra-follicular B cells response following NP-KLH immunization. Immunized uremic mice demonstrated compromised affinity maturation, isotype switching, antigen-specific antibody secreting cells, antibody titer and T follicular helper cells response. Consequently, uremic mice exhibited diminished GC and antibody response following prime-boost immunization. B cells showed increased cell cycle arrest, apoptosis and impaired migration between light and dark zone in the uremic GCs. We identified uremic toxin hippuric acid as a major driver of loss of mitochondrial membrane potential leading to increased apoptosis in mouse and human B cells. Finally, we show that GC B cells, T follicular helper cells and antibody response were similarly diminished in uremic mice during influenza virus infection, a major cause of mortality in patients with kidney disease. These results shed light on how uremic toxin(s) suppress antimicrobial immunity and vaccine response in individuals with kidney disease. Knowledge gained from this study may pave the path for developing effective therapeutic and preventive strategies in uremic patients against infections including SARS-CoV-2. R01AI142354, R01AI162616 and R21AI159058

Role of germinal center response in the antibody responses against SARS-CoV-2 spike protein

Abstract Spike-based vaccination strategies, including mRNA, effectively induce antibody responses against SARS-CoV-2. However, the breadth of antibody responses raised by Wuhan spike covering newly emerging variants remains unclear. Here, we investigate how the loss of function of GC responses and IL-4 signal influence the antibody and memory B cell responses against spike proteins of SARS-CoV-2 variants. In mouse model, immunization of C57BL/6J and C3H mice with trimeric recombinant spike protein of Wuhan-CoV-2 efficiently induced the production of antibodies capable of recognizing the receptor binding domain of delta, and omicron (BA1, and BA5) variants. The third boosting with Wuhan spike protein was also effective in inducing the antibodies to recognize omicron variants, but the boosting with BA5 was only effective for BA5, not Wuhan. We tested the neutralizing activity of these antibodies by the in vitro binding assay using psuedo-virus and human bronchial organoids infection system. These antibodies effectively blocked the infection of Wuhan and delta variants, but the protection was reduced for omicron variants. We further evaluated the contribution of the GC response and IL-4 using Bcl6 deficient mice (Bcl6f/f CD4-cre, Bcl6f/f CD4ER-cre) or B cell-specific deficient mice of the IL-4 receptor(R) (Il4rΔB mice). The results indicated that Bcl6 deficient mice and the mice lacking IL-4R signaling in B cells markedly reduced initial antibody responses and diminished protectivity of the antibodies against the variant virus. In conclusion, our results indicated that the GC response and IL-4 signal provides a quantitative checkpoint optimizing the breadth of anti-SARS-CoV2 protective antibody response.

Subcapsular sinus macrophage infection after viral dissemination to distal lymph nodes maximizes germinal center responses

Abstract Neutralizing antibodies are a hallmark of protective humoral response against many viral infections. Microanatomical structures called germinal centers (GCs) within the secondary lymphoid organs are the sites where B cells get differentiated into high affinity antibody secreting, class switched and long-lasting plasma and memory B cells. Most studies of antigen movement leading to B cell activation have been performed using subcutaneous injection, mimicking the natural route of infection. Under this condition, virus infects sinusoidal lymph node macrophages which relay the antigen to B cells to drive the GC responses. However, not much is known about antigen movement during the generation of GCs in the non-draining (or distal lymph nodes) after systemic viral dissemination. Using ZIKV infection of mice, we have mapped virus dissemination through two separate lymph node chains. Surprisingly, GCs efficiently formed in distal LNs, although with delayed kinetics compared to those directly draining the infection site. Remarkably, virus in the blood alone was not sufficient to produce GCs. Instead, virus still reached the LNs through the lymphatics and infected LN sinusoidal macrophages. This coincided with virus-induced vascular permeability in the tissue. Thus, GC formation still proceeds through sinusoidal LN macrophages even when virus is spread through the blood. Our findings reveal a conserved mechanism for antiviral B cell development in LNs distal from the site of infection.

Alterations in Germinal Center (GC) Formation and B Cell Activation during Severe Orientia tsutsugamushiInfection in Mice

Abstract Scrub typhus is a poorly studied, but life-threatening, disease caused by the bacterium Orientia tsutsugamushi (Ot). Humoral immunity in scrub typhus patients wanes as early as one-year post-infection; yet its underlying mechanisms remain unclear. The objective of this study is to delineate mechanisms underlying humoral immune dysregulation and B cell dysfunction during acute Ot infection. Using a lethal scrub typhus C57BL/6 murine model, we evaluated splenic GC responses by immunofluorescent staining. Splenic germinal centers (GL-7 +cells) were formed at D4, but were nearly absent at D8, accompanied by randomly scattered T cells. Both infection days had comparable numbers of GC B cells and T follicular helper (Tfh) cells, indicating that GC loss at D8 was less likely due to cell death, but rather dysregulation in GC formation. To confirm this hypothesis, we performed RNAseq analysis of purified B220 +B cells and revealed a set of differentially expressed genes associated with B cell adhesion (S1PR1, ICAM1, GPR183) and co-stimulation (CD40, ICOS-L, SLAMF1) at D8. Notably, the downregulation of S1PR2 (a GC-specific adhesion gene) was most evident at D8, correlating to disrupted GC formation. Furthermore, transcriptomic data revealed significant downregulation of 71% B cell activation genes on D8, suggesting attenuation of B cell activation. Additional studies with low- and high-virulence Ot strains and comparative flow cytometry revealed significant differences in both B cell subsets (plasmablasts, marginal zone B cells) and T cell subsets (Tfh and Tfr cells). This is the first study showing marked dysregulation of B cell responses during Ot infection, which helps understand the transient immunity associated with scrub typhus. Supported by grants from NIH (R01 AI132674, R21 AI156536, R21 AI153586, R01 EY028773, T32 AI007526), Department of Defense Threat Reduction Agency grant (HDTRA1-19-1-0043), UTMB IHII Data Acquisition (CIRWH&IHII Pilot/ Phase II Research grant) and UTMB Center for Biodefense and Emerging Infectious Diseases (Pilot grant)

CD9 identifies and regulates a highly functional and unique subset of T follicular helper (Tfh) cells necessary for the promotion of antibodies during infection

Abstract T follicular helper (Tfh) cells comprise a subset of CD4 +T helper (Th) cells phenotypically and functionally distinct from Th1 and Th2 cell subsets. Tfh cells are located within B cell follicles and germinal centers (GC), where they secrete the cytokines IL-21 and interferon-γ (IFN-γ) which aid in B cell proliferation and differentiation. CD9, a tetraspanin, has been shown to accumulate on CD4 T cells at the immunological synapse, playing a role in co-stimulation and stabilization of the synapse via regulation of the integrins LFA-1 and VLA-4. CD9 has been shown to be expressed on activated CD4 T cells, but whether it remains upregulated specifically on Tfh cells is unknown. We identified a distinct population of CD9-expressing Tfh cells (CD9 hi) following acute viral infections and examined their role in promoting GC responses. Following acute LCMV infection, CD9 hiTfh cells are found in the follicles and GCs, yet exhibited enhanced proliferation and migratory capacity to the chemokines CXCL12 and CXCL13. Epigenetically, CD9 hiTfh cells demonstrated a distinct transcriptional profile and chromatin architecture from their CD9 locounterpart, with an upregulation of cell cycling, PI3K, and integrin-regulated genes. Functionally, CD9 hiTfh cells had elevated VLA-4 expression and were the predominant producers of IL-21 and IFN-γ, indicating a specific role in B cell maturation and differentiation. Furthermore, deletion of CD9 did not alter Tfh cell development, but lead to their reduction of IL-21 and IFN-γ production and a decrease in overall antibody responses. Therefore, we identified that CD9 hiTfh cells are a highly functional and unique subset necessary for the promotion of antibodies during infection. R01 AR073912

TRAF3-EWSR1 signaling axis acts as a checkpoint on germinal center responses.

The formation of germinal centers (GCs) is crucial for humoral immunity and vaccine efficacy. Constant stimulation through microbiota drives the formation of constitutive GCs in Peyer's patches (PPs), which generate B cells that produce antibodies against gut antigens derived from commensal bacteria and infectious pathogens. However, the molecular mechanism that regulates this persistent process is poorly understood. We report that Ewing Sarcoma Breakpoint Region 1 (EWSR1) is a brake to constitutive GC generation and immunoglobulin G (IgG) production in PPs, vaccination-induced GC formation, and IgG responses. Mechanistically, EWSR1 suppresses Bcl6 upregulation after antigen encounter, thereby negatively regulating induced GC B cell generation and IgG production. We further showed that tumor necrosis factor receptor-associated factor (TRAF) 3 serves as a negative regulator of EWSR1. These results established that the TRAF3-EWSR1 signaling axis acts as a checkpoint for Bcl6 expression and GC responses, indicating that this axis is a therapeutic target to tune GC responses and humoral immunity in infectious diseases.

Self-replicating RNA nanoparticle vaccine elicits protective immune responses against SARS-CoV-2

The creation of safe and effective vaccines that induce potent cellular and humoral immune responses against SARS-CoV-2 is urgently needed to end the global COVID-19 epidemic. Here, we developed an alphavirus-derived self-replicating RNA (repRNA)-based vaccine platform encoding the receptor-binding domain (RBD) of SARS-CoV-2 spike glycoprotein. The repRNA triggers prolonged antigen expression compared with conventional mRNA due to the replication machinery of repRNA. To improve the delivery and vaccine efficacy of repRNA, we developed a self-assembling liposome-protamine-RNA (LPR) nanoparticle with highly efficient encapsulation and transfection of repRNA. LPR-repRNA vaccines substantially activated type I interferon response and innate immune signaling pathways. Subcutaneous immunization of LPR-repRNA-RBD led to prolonged antigen expression, stimulation of innate immune cells, and induction of germinal center response in draining lymph nodes. LPR-repRNA-RBD induced antigen-specific Tcell responses and skewed cellular immunity toward an effector memory CD8+ Tcell response. Immunizations with LPR-repRNA-RBD triggered the production of anti-RBD IgG antibodies and induced neutralizing antibody response against SARS-CoV-2 pseudovirus. LPR-repRNA-RBD vaccines reduced SARS-CoV-2 infection and lung inflammation in mice. Altogether, these data suggest that the LPR-repRNA platform can be a promising avenue for COVID-19 vaccine development.

The expanding family of T follicular regulatory cells.

The coevolution of multiple specialized T follicular regulatory cell subsets has led to fine-tuning of human germinal center responses in providing optimal antibody production and preventing events leading to autoimmunity (see the related Research Article by Le Coz etal.).

Antibodies against endogenous retroviruses promote lung cancer immunotherapy

B cells are frequently found in the margins of solid tumours as organized follicles in ectopic lymphoid organs called tertiary lymphoid structures (TLS)1,2. Although TLS have been found to correlate with improved patient survival and response to immune checkpoint blockade (ICB), the underlying mechanisms of this association remain elusive1,2. Here we investigate lung-resident B cell responses in patients from the TRACERx 421 (Tracking Non-Small-Cell Lung Cancer Evolution Through Therapy) and other lung cancer cohorts, and in a recently established immunogenic mouse model for lung adenocarcinoma3. We find that both human and mouse lung adenocarcinomas elicit local germinal centre responses and tumour-binding antibodies, and further identify endogenous retrovirus (ERV) envelope glycoproteins as a dominant anti-tumour antibody target. ERV-targeting B cell responses are amplified by ICB in both humans and mice, and by targeted inhibition of KRAS(G12C) in the mouse model. ERV-reactive antibodies exert anti-tumour activity that extends survival in the mouse model, and ERV expression predicts the outcome of ICB in human lung adenocarcinoma. Finally, we find that effective immunotherapy in the mouse model requires CXCL13-dependent TLS formation. Conversely, therapeutic CXCL13 treatment potentiates anti-tumour immunity and synergizes with ICB. Our findings provide a possible mechanistic basis for the association of TLS with immunotherapy response.

SARS-CoV-2 Omicron boosting induces de novo B cell response in humans.

The primary two-dose SARS-CoV-2 mRNA vaccine series are strongly immunogenic in humans, but the emergence of highly infectious variants necessitated additional doses and the development of vaccines aimed at the new variants1-4. SARS-CoV-2 booster immunizations in humans primarily recruit pre-existing memory B cells5-9. However, it remains unclear whether the additional doses induce germinal centre reactions whereby re-engaged B cells can further mature, and whether variant-derived vaccines can elicit responses to variant-specific epitopes. Here we show that boosting with an mRNA vaccine against the original monovalent SARS-CoV-2 mRNA vaccine or the bivalent B.1.351 and B.1.617.2 (Beta/Delta) mRNA vaccine induced robust spike-specific germinal centre B cell responses in humans. The germinal centre response persisted for at least eight weeks, leading to significantly more mutated antigen-specific bone marrow plasma cell and memory B cell compartments. Spike-binding monoclonal antibodies derived from memory B cells isolated from individuals boosted with either the original SARS-CoV-2 spike protein, bivalent Beta/Delta vaccine or a monovalent Omicron BA.1-based vaccine predominantly recognized the original SARS-CoV-2 spike protein. Nonetheless, using a more targeted sorting approach, we isolated monoclonal antibodies that recognized the BA.1 spike protein but not the original SARS-CoV-2 spike protein from individuals who received the mRNA-1273.529 booster; these antibodies were less mutated and recognized novel epitopes within the spike protein, suggesting that they originated from naive B cells. Thus, SARS-CoV-2 booster immunizations in humans induce robust germinal centre B cell responses and can generate de novo B cell responses targeting variant-specific epitopes.

The RNA-binding protein hnRNP F is required for the germinal center B cell response

The T cell-dependent (TD) antibody response involves the generation of high affinity, immunoglobulin heavy chain class-switched antibodies that are generated through germinal center (GC) response. This process is controlled by coordinated transcriptional and post-transcriptional gene regulatory mechanisms. RNA-binding proteins (RBPs) have emerged as critical players in post-transcriptional gene regulation. Here we demonstrate that B cell-specific deletion of RBP hnRNP F leads to diminished production of class-switched antibodies with high affinities in response to a TD antigen challenge. B cells deficient in hnRNP F are characterized by defective proliferation and c-Myc upregulation upon antigenic stimulation. Mechanistically, hnRNP F directly binds to the G-tracts of Cd40 pre-mRNA to promote the inclusion of Cd40 exon 6 that encodes its transmembrane domain, thus enabling appropriate CD40 cell surface expression. Furthermore, we find that hnRNP A1 and A2B1 can bind to the same region of Cd40 pre-mRNA but suppress exon 6 inclusion, suggesting that these hnRNPs and hnRNP F might antagonize each-other’s effects on Cd40 splicing. In summary, our study uncovers an important posttranscriptional mechanism regulating the GC response.

Protein phosphatase 2A propels follicular T helper cell development in lupus

Follicular helper T (Tfh) cells are important for generating humoral immune responses by helping B cells form germinal centers (GCs) and the production of high-affinity antibodies. However, aberrant Tfh cell expansion also contributes to the generation of self-reactive autoantibodies and promotes autoantibody-mediated autoimmune diseases such as systemic lupus erythematosus (SLE). Protein phosphatase 2A catalytic subunit alpha isoform (PP2A Cα) expression levels are elevated in peripheral T cells of SLE patients and positively correlate with autoantibody titers and disease activity. Here, we demonstrate a critical role of PP2A in Tfh differentiation by using T cell restricted PP2A Cα deficient mice. We observed impaired Tfh differentiation and GC response in two different classical Tfh induction models. Mechanistic studies revealed that downregulation of protein translation of the Tfh lineage transcription factor BCL6 in PP2A deficient T cells. Importantly, we found that PP2A deficiency by either gene knockout or chemical inhibition alleviated lupus severity in mice. Lastly, we confirmed a positive correlation between PP2A Cα and BCL6 protein levels in human CD4+ T cells from patients with SLE. In summary, our study revealed a critical role of PP2A in regulating Tfh cells and suggests it is a potential therapeutic target for lupus.

Immune Response Related to Lymphadenopathy Post COVID-19 Vaccination

Mass vaccination against coronavirus disease 2019 (COVID-19) is a global health strategy to control the COVID-19 pandemic. With the increasing number of vaccinations, COVID-19 vaccine-associated lymphadenopathy (C19-VAL) has been frequently reported. Current findings emphasize the characteristics of C19-VAL. The mechanism of C19-VAL is complicated to explore. Accumulated reports separately show that C19-VAL incidence is associated with receiver age and gender, reactive change within lymph nodes (LN), etc. We constructed a systematic review to evaluate the associated elements of C19-VAL and provide the mechanism of C19-VAL. Articles were searched from PubMed, Web of Science and EMBASE by using the processing of PRISMA. The search terms included combinations of the COVID-19 vaccine, COVID-19 vaccination and lymphadenopathy. Finally, sixty-two articles have been included in this study. Our results show that days post-vaccination and B cell germinal center response are negatively correlated with C19-VAL incidence. The reactive change within LN is highly related to C19-VAL development. The study results suggested that strong vaccine immune response may contribute to the C19-VAL development and perhaps through the B cell germinal center response post vaccination. From the perspective of imaging interpretation, it is important to carefully distinguish reactive lymph nodes from metastatic lymph node enlargement through medical history collection or evaluation, especially in patients with underlying malignancy.