Critical role of TSLP-responsive mucosal dendritic cells in the induction of nasal antigen-specific IgA response

High TSLP responses in the human infant airways are associated with pre-activated airway epithelial IFN antiviral immunity

Thymic stromal lymphopoietin (TSLP) is a primarily epithelial-derived cytokine that drives type 2 allergic immune responses. Early life viral respiratory infections elicit high TSLP production, which leads to the development of type 2 inflammation and airway hyperreactivity. The goal of this study was to examine in vivo and in vitro the human airway epithelial responses leading to high TSLP production during viral respiratory infections in early infancy. A total of 129 infants (<1-24 m, median age 10 m) with severe viral respiratory infections were enrolled for in vivo (n = 113), and in vitro studies (n = 16). Infants were classified as 'high TSLP' or 'low TSLP' for values above or below the 50th percentile. High versus low TSLP groups were compared in terms of type I-III IFN responses and production of chemokines promoting antiviral (CXCL10), neutrophilic (CXCL1, CXCL5, CXCL8), and type 2 responses (CCL11, CCL17, CCL22). Human infant airway epithelial cell (AEC) cultures were used to define the transcriptomic (RNAseq) profile leading to high versus low TSLP responses in vitro in the absence (baseline) or presence (stimulated) of a viral mimic (poly I:C). Infants in the high TSLP group had greater in vivo type III IFN airway production (median type III IFN in high TSLP 183.2 pg/mL vs. 63.4 pg/mL in low TSLP group, p = 0.007) and increased in vitro type I-III IFN AEC responses after stimulation with a viral mimic (poly I:C). At baseline, our RNAseq data showed that infants in the high TSLP group had significant upregulation of IFN signature genes (e.g., IFIT2, IFI6, MX1) and pro-inflammatory chemokine genes before stimulation. Infants in the high TSLP group also showed a baseline AEC pro-inflammatory state characterized by increased production of all the chemokines assayed (e.g., CXCL10, CXCL8). High TSLP responses in the human infant airways are associated with pre-activated airway epithelial IFN antiviral immunity and increased baseline AEC production of pro-inflammatory chemokines. These findings present a new paradigm underlying the production of TSLP in the human infant airway epithelium following early life viral exposure and shed light on the long-term impact of viral respiratory illnesses during early infancy and beyond childhood.

Type III interferon exerts thymic stromal lymphopoietin in mediating adaptive antiviral immune response

Previously, it was believed that type III interferon (IFN-III) has functions similar to those of type I interferon (IFN-I). However, recently, emerging findings have increasingly indicated the non-redundant role of IFN-III in innate antiviral immune responses. Still, the regulatory activity of IFN-III in adaptive immune response has not been clearly reported yet due to the low expression of IFN-III receptors on most immune cells. In the present study, we reviewed the adjuvant, antiviral, antitumor, and disease-moderating activities of IFN-III in adaptive immunity; moreover, we further elucidated the mechanisms of IFN-III in mediating the adaptive antiviral immune response in a thymic stromal lymphopoietin (TSLP)-dependent manner, a pleiotropic cytokine involved in mucosal adaptive immunity. Research has shown that IFN-III can enhance the antiviral immunogenic response in mouse species by activating germinal center B (GC B) cell responses after stimulating TSLP production by microfold (M) cells, while in human species, TSLP exerts OX40L for regulating GC B cell immune responses, which may also depend on IFN-III. In conclusion, our review highlights the unique role of the IFN-III/TSLP axis in mediating host adaptive immunity, which is mechanically different from IFN-I. Therefore, the IFN-III/TSLP axis may provide novel insights for clinical immunotherapy.

Protection of hamsters challenged with SARS-CoV-2 after two doses of MVC-COV1901 vaccine followed by a single intranasal booster with nanoemulsion adjuvanted S-2P vaccine

Intramuscular vaccines have greatly reduced hospitalization and death due to severe COVID-19. However, most countries are experiencing a resurgence of infection driven predominantly by the Delta and Omicron variants of SARS-CoV-2. In response, booster dosing of COVID-19 vaccines has been implemented in many countries to address waning immunity and reduced protection against the variants. However, intramuscular boosting fails to elicit mucosal immunity and therefore does not solve the problem of persistent viral carriage and transmission, even in patients protected from severe disease. In this study, two doses of stabilized prefusion SARS-CoV-2 spike (S-2P)-based intramuscular vaccine adjuvanted with Alum/CpG1018, MVC-COV1901, were used as a primary vaccination series, followed by an intranasal booster vaccination with nanoemulsion (NE01)-adjuvanted S-2P vaccine in a hamster model to demonstrate immunogenicity and protection from viral challenge. Here we report that this vaccination regimen resulted not only in the induction of robust immunity and protection against weight loss and lung pathology following challenge with SARS-CoV-2, but also led to increased viral clearance from both upper and lower respiratory tracts. Our findings showed that intramuscular MVC-COV1901 vaccine followed by a booster with intranasal NE01-adjuvanted vaccine promotes protective immunity against both viral infection and disease, suggesting that this immunization protocol may offer a solution in addressing a significant, unmet medical need for both the COVID-19 and future pandemics.

Interferon-λ Improves the Efficacy of Intranasally or Rectally Administered Influenza Subunit Vaccines by a Thymic Stromal Lymphopoietin-Dependent Mechanism

Previous work showed that interferon-λ (IFN-λ) can trigger the synthesis of thymic stromal lymphopoietin (TSLP) by specialized epithelial cells in the upper airways of mice, thereby improving the performance of intranasally administered influenza vaccines. Here we demonstrate that protein-only influenza vaccines containing either IFN-λ or TSLP boosted antigen-specific IgG1 and IgA responses and enhanced the resistance of mice to influenza virus challenge, irrespective of whether the vaccines were applied via the intranasal or the rectal route. TSLP receptor deficiency negatively influenced vaccine-induced antiviral immunity by impairing the migration of dendritic cells from the airways to the draining lymph nodes of immunized mice, thereby restraining follicular helper T cell and germinal center B cell responses. As previously observed during intranasal vaccination, the adjuvant effect of IFN-λ on a rectally administered influenza vaccine was no longer observed when TSLP receptor-deficient mice were used for immunization, highlighting the central role of the IFN-λ/TSLP axis for vaccine-induced antiviral immunity in the mucosa.

Epithelial Barrier Dysfunction in Chronic Respiratory Diseases

Mucosal surfaces are lined by epithelial cells, which provide a complex and adaptive module that ensures first-line defense against external toxics, irritants, antigens, and pathogens. The underlying mechanisms of host protection encompass multiple physical, chemical, and immune pathways. In the lung, inhaled agents continually challenge the airway epithelial barrier, which is altered in chronic diseases such as chronic obstructive pulmonary disease, asthma, cystic fibrosis, or pulmonary fibrosis. In this review, we describe the epithelial barrier abnormalities that are observed in such disorders and summarize current knowledge on the mechanisms driving impaired barrier function, which could represent targets of future therapeutic approaches.

Asthma-Associated Long TSLP Inhibits the Production of IgA

Thymic stromal lymphopoietin (TSLP) contributes to asthmatic disease. The concentrations of protective IgA may be reduced in the respiratory tract of asthma patients. We investigated how homeostatic short TSLP (shTSLP) and asthma-associated long TSLP (loTSLP) regulate IgA production. B cells from healthy donors were stimulated in the presence or absence of shTSLP or loTSLP; the concentrations of IgA, IgM, IgE, and IgG antibodies were determined in cell culture supernatants; and B cells were analyzed by flow cytometry. LoTSLP, but not shTSLP, suppressed the secretion of IgA but not of IgE. The type 2 cytokine IL-4, which in addition to loTSLP contributes to asthmatic disease, did not affect the production of IgA or the frequency of IgA+ B cells. Instead, IL-4 increased IgG production, especially of the subclasses IgG2 and IgG4. LoTSLP inhibited IgA secretion by sorted memory B cells but not by naïve B cells. Although loTSLP inhibited IgA production, the vitamin A metabolite retinoic acid promoted the secretion of IgA, also in the presence of loTSLP, suggesting that vitamin A may promote IgA production in asthma. Our data demonstrate that asthma-associated loTSLP negatively regulates the secretion of IgA, which may negatively impact the surveillance of mucosal surfaces in asthma.

The central role of the nasal microenvironment in the transmission, modulation, and clinical progression of SARS-CoV-2 infection

The novel coronavirus SARS-CoV-2 enters into the human body mainly through the ACE2 + TMPRSS2+ nasal epithelial cells. The initial host response to this pathogen occurs in a peculiar immune microenvironment that, starting from the Nasopharynx-Associated Lymphoid Tissue (NALT) system, is the product of a long evolutionary process that is aimed to first recognize exogenous airborne agents. In the present work, we want to critically review the latest molecular and cellular findings on the mucosal response to SARS-CoV-2 in the nasal cavity and in NALT, and to analyze its impact in the subsequent course of COVID-19. Finally, we want to explore the possibility that the regulation of the systemic inflammatory network against the virus can be modulated starting from the initial phases of the nasal and nasopharyngeal response and this may have several clinical and epidemiological implications starting from a mucosal vaccine development.

The Protective HIV-1 Envelope gp41 Antigen P1 Acts as a Mucosal Adjuvant Stimulating the Innate Immunity

Mucosal nasal vaccine development, although ideal to protect from pathogens invading mucosally, is limited by the lack of specific adjuvant. We recently used P1, a conserved region of HIV-1 gp41-envelope glycoprotein, as efficient antigen in a prophylactic HIV-1 mucosal vaccine applied nasally. Herein, P1 immunomodulation properties were assessed on human nasal mucosal models by measuring induction of cytokine and chemokine production, intracellular signaling pathways, mucosal dendritic cell (DC) activation, and T cell proliferation. P1 adjuvant properties were evaluated by quantification of antigen-specific B cell responses against a model antigen in an in vitro immunization model. We now demonstrated that P1 has additional immunological properties. P1 initiates immune responses by inducing nasal epithelial cells to secrete the Th2-cytokine thymic stromal lymphopoietin (TSLP), a described mucosal adjuvant. Secreted TSLP activates, in turn, intracellular calcium flux and PAR-2-associated NFAT signaling pathway regulated by microRNA-4485. Thereafter, P1 induces mucosal dendritic cell maturation, secretion of TSLP in a TSLP-receptor (R)-dependent autocrine loop, but also IL-6, IL-10, IL-8, CCL20, CCL22, and MMP-9, and proliferation of CD4+ T cells. Finally, P1 acts as an adjuvant to stimulate antigen-specific B cell responses in vitro. Overall, P1 is a multi-functional domain with various immuno-modulatory properties. In addition to being a protective vaccine antigen for HIV prevention, P1 acts as adjuvant for other mucosal vaccines able to stimulate humoral and cellular antigen-specific responses.

Preclinical Efficacy of a Trivalent Human FcγRI-Targeted Adjuvant-Free Subunit Mucosal Vaccine against Pulmonary Pneumococcal Infection

Lack of safe and effective mucosal adjuvants has severely hampered the development of mucosal subunit vaccines. In this regard, we have previously shown that immunogenicity of vaccine antigens can be improved by targeting the antigens to the antigen-presenting cells. Specifically, groups of mice immunized intranasally with a fusion protein (Bivalent-FP) containing a fragment of pneumococcal-surface-protein-A (PspA) as antigen and a single-chain bivalent antibody raised against the anti-human Fc-gamma-receptor-I (hFcγRI) elicited protective immunity to pulmonary Streptococcus pneumoniae infection. In order to further enhance the immunogenicity, an additional hFcγRI-binding moiety of the single chain antibody was incorporated. The modified vaccine (Trivalent-FP) induced significantly improved protection against lethal pulmonary S. pneumoniae challenge compared to Bivalent-FP. In addition, the modified vaccine exhibited over 85% protection with only two immunizations. Trivalent-FP also induced S. pneumoniae-specific systemic and mucosal antibodies. Moreover, Trivalent-FP also induced IL-17- and IL-22-producing CD4⁺ T cells. Furthermore, it was found that the hFcγRI facilitated uptake and presentation of Trivalent-FP. In addition, Trivalent-FP also induced IL-1α, MIP-1α, and TNF-α; modulated recruitment of dendritic cells and macrophages; and induced CD80/86 and MHC-II expression on antigen presenting cells.

Toll-Like Receptor 2 (TLR2) and TLR4 Mediate the IgA Immune Response Induced by Mycoplasma hyopneumoniae

IgA plays an important role in mucosal immunity against infectious pathogens; however, the molecular mechanism of IgA secretion in response to infection remains largely unknown, particularly in Mycoplasma spp. In this study, we found that the levels of IgA in the peripheral blood serum, bronchoalveolar lavage fluid, nasal mucosa, trachea, hilar lymph nodes, and lung tissues of pigs increased significantly after infection with Mycoplasma hyopneumoniae.

IgA plays an important role in mucosal immunity against infectious pathogens; however, the molecular mechanism of IgA secretion in response to infection remains largely unknown, particularly in Mycoplasma spp. In this study, we found that the levels of IgA in the peripheral blood serum, bronchoalveolar lavage fluid, nasal mucosa, trachea, hilar lymph nodes, and lung tissues of pigs increased significantly after infection with Mycoplasma hyopneumoniae. Furthermore, IgA and CD11c were detected in the lungs and hilar lymph nodes by immunohistochemical analysis, and colocalization of these two markers indicates that CD11c⁺ cells play an important role in IgA mucosal immunity induced by M. hyopneumoniae. To investigate the regulatory mechanism of IgA, we separated mouse dendritic cells (DCs) from different tissues and mouse macrophages from the lungs and then cultured mouse B cells together with either DCs or macrophages in vitro. In the mouse lung-DC/B (LDC/B) cell coculture, IgA secretion was increased significantly after the addition of whole-cell lysates of M. hyopneumoniae. The expression of both Toll-like receptor 2 (TLR2) and TLR4 was also upregulated, as determined by mRNA and protein expression analyses, whereas no obvious change in the expression of TLR3 and TLR7 was detected. Moreover, the IgA level decreased to the same as the control group when TLR2 or TLR4 was inhibited instead of TLR8 or TLR7/9. In conclusion, M. hyopneumoniae can stimulate the response of IgA through TLR2 and TLR4 in a mouse LDC/B cell coculture model, and the coculture model is an ideal tool for studying the IgA response mechanism, particularly that with Mycoplasma spp.

Reappraisal of antibodies against Saccharomyces cerevisiae (ASCA) as persistent biomarkers in quiescent Crohn's disease

A clear correlation exists between microbiota and the dysregulation of the immune response in Inflammatory Bowel Diseases (IBD), which comprise Crohn's disease (CD) and ulcerative colitis (UC). These unbalanced reactions also involve humoral responses, with antibodies against Saccharomyces cerevisiae. Thus, here we aimed to quantify IgA and IgG specific to S. cerevisiae (ASCA) in quiescent CD and UC, to correlate the production of these antibodies with patient's inflammatory response and disease clinical presentation. Twenty-nine subjects (16 CD and 13 UC) and 45 healthy controls were enrolled in this study and had plasma samples tested for ASCA and cytokines (IL-2, IL-4, IL-6, IL-10, IFN-γ, TNF-α), besides clinical evaluation. IBD patients had increase IgA and IgG ASCA, especially those with colonic (L2) and fistulizing (B3) CD. Similarly, patients who dropped out the treatment had augmented ASCA, while IgG was reduced in those receiving sulfasalazine treatment. Furthermore, the quiescent CD patients had elevated IL-6 on plasma, especially in the absence of treatment, together with increased counter regulatory response of IL-10. There was a positive correlation between IgA and IgG on CD but not UC, as well as between IgA and TNF in total IBD patients. In addition, the levels of IgG x TNF, IgA x IL-10 and IgG x IL-10 were also correlated in CD, indicating that ASCA production may be influenced by the inflammatory response. Finally, we concluded that ASCA could be pointed as relevant biomarker of CD presentation and residual inflammation, even in clinical remission patients.

Interferon-λ enhances adaptive mucosal immunity by boosting release of thymic stromal lymphopoietin

Interferon-λ (IFN-λ) acts on mucosal epithelial cells and thereby confers direct antiviral protection. In contrast, the role of IFN-λ in adaptive immunity is far less clear. Here, we report that mice deficient in IFN-λ signaling exhibited impaired CD8⁺ T cell and antibody responses after infection with a live-attenuated influenza virus. Virus-induced release of IFN-λ triggered the synthesis of thymic stromal lymphopoietin (TSLP) by M cells in the upper airways that, in turn, stimulated migratory dendritic cells and boosted antigen-dependent germinal center reactions in draining lymph nodes. The IFN-λ-TSLP axis also boosted production of the immunoglobulins IgG1 and IgA after intranasal immunization with influenza virus subunit vaccines and improved survival of mice after challenge with virulent influenza viruses. IFN-λ did not influence the efficacy of vaccines applied by subcutaneous or intraperitoneal routes, indicating that IFN-λ plays a vital role in potentiating adaptive immune responses that initiate at mucosal surfaces.

Mesenteric CD103+DCs Initiate Switched Coxsackievirus B3 VP1-Specific IgA Response to Intranasal Chitosan-DNA Vaccine Through Secreting BAFF/IL-6 and Promoting Th17/Tfh Differentiation

Intranasal chitosan-formulated DNA vaccination promotes IgA secretion in the intestine. However, the mechanism whereby chitosan-DNA skews IgA class switch recombination (CSR) of B cells in the Gut-associated lymph tissue (GALT) is not fully resolved. In this study, we investigated the effects of nasally administered chitosan-DNA (pcDNA3.1-VP1 plasmid encoding VP1 capsid protein of Coxsackievirus B3) on IgA production, DC activation and Tfh/Th17 response in the intestine. Compared to DNA immunization, intranasal chitosan-DNA vaccination induced antigen-specific IgA production in feces, a pronounced switching of antigen-specific IgA⁺ plasmablast B cells in the mesenteric lymph nodes (MLNs) and an enhanced expression of post-recombination Iα-CH transcripts/IgA germline transcript (αGT) as well as activation-induced cytidine deaminase (AID) in MLN B cells. MLN Tfh frequency was markedly enhanced by chitosan-DNA, and was associated with VP1-specific IgA titer. 24 h after immunization, intranasal chitosan-DNA induced a recruitment of CD103⁺DCs into the MLN that paralleled a selective loss of CD103⁺DCs in the lamina propria (LP). In vivo activated MLN-derived CD103⁺DCs produced high levels of IL-6 and BAFF in response to chitosan-DNA, which up-regulated transmembrane activator and CAML interactor (TACI) expression on MLN B cells. Upon co-culture with IgM⁺B in the presence of chitosan-DNA, MLN CD103⁺DCs induced IgA production in a T-dependent manner; and this IgA-promoting effect of CD103⁺DC was blocked by targeting TACI and, to a lower extent, by blocking IL-6. MLN CD103⁺DCs displayed an enhanced capacity to induce an enhanced CD4⁺Th17 response in vivo and in vitro, and IL-17A deficient mice had a pronounced reduction of specific intestinal IgA following immunization. Taken together, mesenteric CD103⁺DCs are indispensable for the adjuvant activity of chitosan in enhancing DNA vaccine-specific IgA switching in gut through activating BAFF-TACI and IL-6-IL-6R signaling, and through inducing Th17/Tfh differentiation in the MLN.

A tetrameric form of CD40 ligand with potent biological activities in both mouse and human primary B cells

CD40 ligand (CD40 L) expressed by activated T cells interacts with CD40 on B cells and triggers B cell survival, proliferation and differentiation. Deficiency in CD40 L or CD40 in humans causes hyper IgM syndrome due to a defect in T-B interaction that is essential for Ig gene class switch recombination (CSR). CD40 L belongs to the tumor necrosis factor family and normally forms a homotrimer on the cell surface, which is important for its biological activity. To generate a multimeric CD40 L that can be used to stimulate both mouse and human B cells, we fused the extracellular domain of mouse CD40 L, which is known to also bind human CD40, with streptavidin (SA) that forms a stable tetramer under physiological conditions. As expected, 293 T cells transiently transfected with an SA-CD40 L expression vector secreted tetrameric SA-CD40 L in the culture supernatant. The secreted SA-CD40 L exhibited > 25-fold stronger activities in inducing the survival, activation and proliferation of both mouse and human primary B cells than did an agonistic anti-mouse or anti-human CD40 antibody. In the presence of IL-4, SA-CD40 L also induced efficient CSR and plasma cell differentiation in both mouse and human B cells. Moreover, administration of SA-CD40 L in mice induced activation and proliferation of spleen B cells in vivo. These results demonstrate that the SA-CD40 L fusion protein generated in the present study recapitulates the function of membrane-bound trimeric CD40 L and has potent biological activities in both mouse and human primary B cells.

Polymeric Caffeic Acid Is a Safer Mucosal Adjuvant That Augments Antigen-Specific Mucosal and Systemic Immune Responses in Mice

Infections remain a major threat to human lives. To overcome the threat caused by pathogens, mucosal vaccines are considered a promising strategy. However, no inactivated and/or subunit mucosal vaccine has been approved for human use, largely because of the lack of a safe and effective mucosal adjuvant. Here, we show that enzymatically synthesized polymeric caffeic acid (pCA) can act as a potent mucosal adjuvant in mice. Intranasal administration of ovalbumin (OVA) in combination with pCA resulted in the induction of OVA-specific mucosal IgA and serum IgG, especially IgG1. Importantly, pCA was synthesized from caffeic acid and horseradish peroxidase from coffee beans and horseradish, respectively, which are commonly consumed. Therefore, pCA is believed to be a highly safe material. In fact, administration of pCA did not show distinct toxicity in mice. These data indicate that pCA has merit for use as a mucosal adjuvant for nasal vaccine formulations.

Immunity to gastrointestinal nematode infections

Numerous species of nematodes have evolved to inhabit the gastrointestinal tract of animals and humans, with over a billion of the world's population infected with at least one species. These large multicellular pathogens present a considerable and complex challenge to the host immune system given that individuals are continually exposed to infective stages, as well as the high prevalence in endemic areas. This review summarizes our current understanding of host-parasite interactions, detailing induction of protective immunity, mechanisms of resistance, and resolution of the response. It is clear from studies of well-defined laboratory model systems that these responses are dominated by innate and adaptive type 2 cytokine responses, regulating cellular and soluble effectors that serve to disrupt the niche in which the parasites live by strengthening the physical mucosal barrier and ultimately promoting tissue repair.

Development of a nanogel-based nasal vaccine as a novel antigen delivery system

INTRODUCTION

Nasal vaccination is one of the most effective immunization methods because it can induce effective antigen-specific immune responses not only at the mucosal site of administration but also at distant mucosal surfaces, as well as in the systemic compartment. Based on this advantage, many nasal vaccines are being developed and some have been licensed and marketed for clinical use. However, some have been withdrawn because of unacceptable adverse events such as inactivated influenza vaccine administrated with a heat-labile enterotoxin of Escherichia coli as an adjuvant. Thus, it is important to consider both the efficacy and safety of nasal vaccines. Areas covered: This review describes the benefits of cholesteryl group-bearing pullulan (CHP) nanogels for nasal vaccine delivery and vaccine development identified on Pubmed database with the term 'Nanogel-based nasal vaccine'. Expert commentary: CHP nanogels have been developed as novel drug delivery system, and a cationic CHP nanogels have been demonstrated to induce effective immunity as a nasal vaccine antigen carrier. Since vaccine antigens incorporated into CHP nanogels have exhibited no brain deposition after nasal administration in mice and nonhuman primates, the vaccine seems safe, and could be a promising new delivery system.

The Role of BAFF System Molecules in Host Response to Pathogens

The two ligands B cell-activating factor of the tumor necrosis factor family (BAFF) and a proliferation-inducing ligand (APRIL) and the three receptors BAFF receptor (BAFF-R), transmembrane activator and calcium-modulating cyclophilin ligand interactor (TACI), and B cell maturation antigen (BCMA) are members of the "BAFF system molecules." BAFF system molecules are primarily involved in B cell homeostasis. The relevance of BAFF system molecules in host responses to microbial assaults has been investigated in clinical studies and in mice deficient for each of these molecules. Many microbial products modulate the expression of these molecules. Data from clinical studies suggest a correlation between increased expression levels of BAFF system molecules and elevated B cell responses. Depending on the pathogen, heightened B cell responses may strengthen the host response or promote susceptibility. Whereas pathogen-mediated increases in the expression levels of the ligands and/or the receptors appear to promote microbial clearance, certain pathogens have evolved to ablate B cell responses by suppressing the expression of TACI and/or BAFF-R on B cells. Other than its well-established role in B cell responses, the TACI-mediated activation of macrophages is also implicated in resistance to intracellular pathogens. An improved understanding of the role that BAFF system molecules play in infection may assist in devising novel strategies for vaccine development.