Mucosa-associated lymphoid tissues in the aerodigestive tract: their shared and divergent traits and their importance to the orchestration of the mucosal immune system

As inductive tissues for the initiation of antigen-specific T and B cell responses, the various mucosa-associated lymphoid tissues (MALT) of the aerodigestive tract, which include gut-associated lymphoid tissue (GALT), nasopharynx-associated lymphoid tissue (NALT) and bronchus-associated lymphoid tissue (BALT), share many histological and immunological characteristics. However, recent advances in our molecular and cellular understanding of immunological development have revealed that the various types of MALT also exhibit different molecular and cellular interactions for their organogenesis. In this review, we delineate the distinctive features of GALT, NALT and BALT and seek to show the role played by those features in the regulation of mucosal tissue organogenesis, the mucosal immune system, and mucosal homeostasis, all in an attempt to provide insights which might lead to a prospective mucosal vaccine.     

C-Terminal Clostridium perfringens Enterotoxin-Mediated Antigen Delivery for Nasal Pneumococcal Vaccine

Efficient vaccine delivery to mucosal tissues including mucosa-associated lymphoid tissues is essential for the development of mucosal vaccine. We previously reported that claudin-4 was highly expressed on the epithelium of nasopharynx-associated lymphoid tissue (NALT) and thus claudin-4-targeting using C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE) effectively delivered fused antigen to NALT and consequently induced antigen-specific immune responses. In this study, we applied the C-CPE-based vaccine delivery system to develop a nasal pneumococcal vaccine. We fused C-CPE with pneumococcal surface protein A (PspA), an important antigen for the induction of protective immunity against Streptococcus pneumoniae infection, (PspA-C-CPE). PspA-C-CPE binds to claudin-4 and thus efficiently attaches to NALT epithelium, including antigen-sampling M cells. Nasal immunization with PspA-C-CPE induced PspA-specific IgG in the serum and bronchoalveolar lavage fluid (BALF) as well as IgA in the nasal wash and BALF. These immune responses were sufficient to protect against pneumococcal infection. These results suggest that C-CPE is an efficient vaccine delivery system for the development of nasal vaccines against pneumococcal infection.     

Characterization of a B220+ lymphoid cell subpopulation with immune modulatory functions in nasal-associated lymphoid tissues

Complex mechanisms operate on mucosal tissues to regulate immune responsiveness and tolerance. When the lymphocyte subpopulations from murine nasal-associated lymphoid tissues (NALT) were characterized, we observed an accumulation of B220(low)CD3(low)CD4(-)CD8(-)CD19(-)c-Kit(+) cells. TCR transgenic mice and athymic mice were used for monitoring T cell lineage and the presence of extrathymic T cell precursors. The majority of cells from NALT exhibited a T cell precursor phenotype (CD4(-)CD8(-)CD19(-)c-Kit(+)). Fas-independent apoptosis was their main mechanism of cell death. We also demonstrated that B220(low)CD4(-)CD8(-)CD19(-) cells from NALT exhibited the potential to down-regulate the activation of mature T cells. However, the innate immunity receptor TLR2 was also highly expressed by this cell subpopulation. Moreover, nasal stimulation with a TLR2/6 agonist resulted in a partial activation of the double-negative cells. These results suggest that the immune responses in NALT may be in part modulated by a cell subpopulation that maintains a tolerogenic milieu by its proapoptotic status and suppressive activity, which can be reverted through stimulation of a TLR signaling cascade.     

Trachea,lung, and tracheobronchial lymph nodes are the major sites where antigen-presenting cells are detected after nasal vaccination of mice with human papillomavirus type 16 virus-like particles

Vaccination by the nasal route has been successfully used for the induction of immune responses. Either the nasal-associated lymphoid tissue (NALT), the bronchus-associated lymphoid tissue, or lung dendritic cells have been mainly involved. Following nasal vaccination of mice with human papillomavirus type 16 (HPV16) virus-like-particles (VLPs), we have previously shown that interaction of the antigen with the lower respiratory tract was necessary to induce high titers of neutralizing antibodies in genital secretions. However, following a parenteral priming, nasal vaccination with HPV16 VLPs did not require interaction with the lung to induce a mucosal immune response. To evaluate the contribution of the upper and lower respiratory tissues and associated lymph nodes (LN) in the induction of humoral responses against HPV16 VLPs after nasal vaccination, we localized the immune inductive sites and identified the antigen-presenting cells involved using a specific CD4(+) T-cell hybridoma. Our results show that the trachea, the lung, and the tracheobronchial LN were the major sites responsible for the induction of the immune response against HPV16 VLP, while the NALT only played a minor role. Altogether, our data suggest that vaccination strategies aiming to induce efficient immune responses against HPV16 VLP in the female genital tract should target the lower respiratory tract.     

Examining the Role of Nasopharyngeal-associated Lymphoreticular Tissue (NALT) in Mouse Responses to Vaccines

The nasopharyngeal-associated lymphoreticular tissues (NALT) found in humans, rodents, and other mammals, contribute to immunity in the nasal sinuses^1-3. The NALT are two parallel bell-shaped structures located in the nasal passages above the hard palate, and are usually considered to be secondary components of the mucosal-associated lymphoid system^4-6. Located within the NALT are discrete compartments of B and T lymphocytes interspersed with antigen-presenting dendritic cells^4,7,8. These cells are surrounded by an epithelial cell layer intercalated with M-cells that are responsible for antigen retrieval from the mucosal surfaces of the air passages^9,10. Naive lymphocytes circulating through the NALT are poised to respond to first encounters with respiratory pathogens⁷. While NALT disappear in humans by the age of two years, the Waldeyer''s Ring and similarly structured lymphatic organs continue to persist throughout life⁶. In contrast to humans, mice retain NALT throughout life, thus providing a convenient animal model for the study of immune responses originating within the nasal sinuses¹¹.Cultures of single-cell suspensions of NALT are not practical due to low yields of mononuclear cells. However, NALT biology can be examined by ex vivo culturing of the intact organ, and this method has the additional advantage of maintaining the natural tissue structure. For in vivo studies, genetic knockout models presenting defects limited to NALT are not currently available due to a poor understanding of the developmental pathway. For example, while lymphotoxin-α knockout mice have atrophied NALT, the Peyer''s patches, peripheral lymph nodes, follicular dendritic cells and other lymphoid tissues are also altered in these genetically manipulated mice^12,13. As an alternative to gene knockout mice, surgical ablation permanently eliminates NALT from the nasal passage without affecting other tissues. The resulting mouse model has been used to establish relationships between NALT and immune responses to vaccines^1,3. Serial collection of serum, saliva, nasal washes and vaginal secretions is necessary for establishing the basis of host responses to vaccination, while immune responses originating directly from NALT can be confirmed by tissue culture. The following procedures outline the surgeries, tissue culture and sample collection necessary to examine local and systemic humoral immune responses to intranasal (IN) vaccination.     

Cutting edge: organogenesis of nasal-associated lymphoid tissue (NALT) occurs independently of lymphotoxin-alpha (LT alpha) and retinoic acid receptor-related orphan receptor-gamma, but the organization of NALT is LT alpha dependent.

Peyer's patch and nasal-associated lymphoid tissue (NALT) are mucosal lymphoid tissues that appear similar in structure and function. Surprisingly, we found that NALT, unlike Peyer's patch, was formed independently of lymphotoxin (LT)alpha. Furthermore, using mice deficient in the retinoic acid receptor-related orphan receptor-gamma, we found that NALT was formed in the absence of CD4+CD3- cells, which are thought to be the embryonic source of LTalpha. However, we also found that NALT of LTalpha-/- animals was disorganized and lymphopenic, suggesting that the organization and recruitment of lymphocytes within NALT remained dependent on LTalpha. Finally, we demonstrated that both the structure and function of NALT were restored in LTalpha-/- animals upon reconstitution with normal bone marrow. These results demonstrate that the organogenesis of NALT occurs through unique mechanisms.     

Serum antibody response and nasal lymphoid tissue (NALT) structure in the absence of IL-4 or IFN-gamma

Immunization via the nasal route is effective for inducing not only mucosal immunity but also antibody (Ab) response in serum. Nasal lymphoid tissue (NALT) is important for induction of systemic immunity. It remains controversial which T effector cell response is important for serum Ab response after nasal immunization. We investigated serum Ab responses and NALT structures in interleukin (IL)-4 gene targeted (IL-4(-/-)) and interferon (IFN)-gamma gene targeted (IFN-gamma(-/-)) mice. Mice were immunized via nostrils with ovalbumin (OVA) and cholera toxin as adjuvant and serum Ab titers were measured 1 week after final antigen challenge. OVA-specific IgG titers in sera of IL-4(-/-) mice indicated a Th(1) type response, whereas titers in IFN-gamma(-/-) mice and wild-type mice indicated a Th(2) type response. Enhanced serum Ab responses were observed in IL-4(-/-) mice but not IFN-gamma(-/-) mice. OVA-specific Ab-forming cells were detected in the cervical draining lymph nodes but were rare or absent in and around the NALT of all strains of mice. Numbers of OVA-specific Ab-forming cells in cervical lymph nodes were significantly higher in IL-4(-/-) mice than in wild-type and IFN-gamma(-/-) mice. Germinal centers of lymphoid follicles were present in NALT of IL-4(-/-) and other mice. Immunohistochemistry for B and T cell markers revealed that NALT of all mice had approximately the same cellular compositions. Although the absence of IL-4 had no effect on NALT structure, IL-4 may suppress induction of serum Ab responses by nasal immunization.     

Nasal-associated lymphoid tissue is a mucosal inductive site for virus-specific humoral and cellular immune responses

Peyer's patches are known as mucosal inductive sites for humoral and cellular immune responses in the gastrointestinal tract. In contrast, functionally equivalent structures in the respiratory tract remain elusive. It has been suggested that nasal-associated lymphoid tissue (NALT) might serve as a mucosal inductive site in the upper respiratory tract. However, typical signs of mucosal inductive sites like development of germinal center reactions after Ag stimulation and isotype switching of naive B cells to IgA production have not been directly demonstrated. Moreover, it is not known whether CTL can be generated in NALT. To address these issues, NALT was structurally and functionally analyzed using a model of intranasal infection of C3H mice with reovirus. FACS and histological analyses revealed development of germinal centers in NALT in parallel with generation and expansion of IgA(+) and IgG2a(+) B cells after intranasal reovirus infection. Reovirus-specific IgA was produced in both the upper respiratory and the gastrointestinal tract, whereas production of reovirus-specific IgG2a was restricted to NALT, submandibular, and mesenteric lymph nodes. Moreover, virus-specific CTL were detected in NALT. Limiting dilution analysis showed a 5- to 6-fold higher precursor CTL frequency in NALT compared with a cervical lymph node. Together these data provide direct evidence that NALT is a mucosal inductive site for humoral and cellular immune responses in the upper respiratory tract.     

Upper respiratory tract resistance to influenza infection is not prevented by the absence of either nasal-associated lymphoid tissue or cervical lymph nodes

The murine nasal-associated lymphoid tissue (NALT) and cervical lymph nodes (CLN) are involved in the generation of local immune responses within the upper respiratory tract (URT). However, their involvement in these responses does not imply the necessity for resistance to URT infections. We surgically removed NALT or CLN to address the necessity of these lymphatic tissues for the development of a local protective immune response after a URT influenza infection. No histological evidence of the re-establishment of either tissue was detected after surgery and the subsequent infection. Removal of NALT did not elicit changes in serum or nasal mucosa-associated influenza-specific Ig levels. However, increases in PR8-specific serum IgG and nasal mucosa-associated IgA were detected after removal of CLN. Recruitment of influenza-specific CD4 T cells into the nasal mucosa was not altered by removal of NALT. The removal of NALT or CLN did not alter the recruitment of influenza-specific CD8 T cells into the URT. However, increased levels of influenza-specific CD8 T cells were observed in the tracheal-bronchial lymph nodes after CLN surgery. The rate of viral clearance from nasal mucosa and lungs was not altered by removal of NALT or CLN. These studies demonstrate that despite the participation of NALT and CLN in the generation of local immunity to influenza infections, neither tissue is essential for the development of protective immunity and viral clearance in URT.     

Characteristics of Nasal-Associated Lymphoid Tissue (NALT) and Nasal Absorption Capacity in Chicken

As the main mucosal immune inductive site of nasal cavity, nasal-associated lymphoid tissue (NALT) plays an important role in both antigen recognition and immune activation after intranasal immunization. However, the efficiency of intranasal vaccines is commonly restricted by the insufficient intake of antigen by the nasal mucosa, resulting from the nasal mucosal barrier and the nasal mucociliary clearance. The distribution of NALT and the characteristic of nasal cavity have already been described in humans and many laboratory rodents, while data about poultry are scarce. For this purpose, histological sections of the chicken nasal cavities were used to examine the anatomical structure and histological characteristics of nasal cavity. Besides, the absorptive capacity of chicken nasal mucosa was also studied using the materials with different particle size. Results showed that the NALT of chicken was located on the bottom of nasal septum and both sides of choanal cleft, which mainly consisted of second lymphoid follicle. A large number of lymphocytes were distributed under the mucosal epithelium of inferior nasal meatus. In addition, there were also diffuse lymphoid tissues located under the epithelium of the concha nasalis media and the walls of nasal cavity. The results of absorption experiment showed that the chicken nasal mucosa was capable to absorb trypan blue, OVA, and fluorescent latex particles. Inactivated avian influenza virus (IAIV) could be taken up by chicken nasal mucosa except for the stratified squamous epithelium sites located on the forepart of nasal cavity. The intake of IAIV by NALT was greater than that of the nasal mucosa covering on non-lymphoid tissue, which could be further enhanced after intranasal inoculation combined with sodium cholate or CpG DNA. The study on NALT and nasal absorptive capacity will be benefit for further understanding of immune mechanisms after nasal vaccination and development of nasal vaccines for poultry.     

Antigen-specific CD8(+) T cells persist in the upper respiratory tract following influenza virus infection.

Because little is known about lymphocyte responses in the nasal mucosa, lymphocyte accumulation in the nasal mucosa, nasal-associated lymphoid tissue (NALT), and cervical lymph nodes (CLN) were determined after primary and heterosubtypic intranasal influenza challenge of mice. T cell accumulation peaked in the nasal mucosa on day 7, but peaked slightly earlier in the CLN (day 5) and later (day 10) in the NALT. Tetrameric staining of nasal mucosal cells revealed a peak accumulation of CD8 T cells specific for either the H-2D(b) influenza nucleoprotein epitope 366-374 (D(b)NP(366)) or the H-2D(b) polymerase 2 protein epitope 224-233 (D(b)PA(224)) at 7 days. By day 13, D(b)PA(224)-specific CD8 T cells were undetectable in the mucosa, whereas D(b)NP(366)-specific CD8 T cells persisted for at least 35 days in the mucosa and spleen. After heterosubtypic virus challenge, the accumulation of CD8 T cells in the nasal mucosa was quicker, more intense, and predominantly D(b)NP(366) specific relative to the primary inoculation. The kinetics and specificity of the CD8 T cell response were similar to those in the CLN, but the responses in the NALT and spleen were again slower and more protracted. These results indicate that similar to what was reported in the lung, D(b)NP(366)-specific CD8 T cells persist in the nasal mucosa after primary influenza infection and predominate in an intensified nasal mucosal response to heterosubtypic challenge. In addition, differences in the kinetics of the CD8 T cell responses in the CLN, NALT, and spleen suggest different roles of these lymphoid tissues in the mucosal response.     

Nasal-associated lymphoid tissue: phenotypic and functional evidence for the primary role of peripheral node addressin in naive lymphocyte adhesion to high endothelial venules in a mucosal site.

Nasal-associated lymphoid tissue (NALT), a mucosal inductive site for the upper respiratory tract, is important for the development of mucosal immunity locally and distally to intranasally introduced Ag. To more fully understand the induction of nasal mucosal immunity, we investigated the addressins that allow for lymphocyte trafficking to this tissue. To investigate the addressins responsible for naive lymphocyte binding, immunofluorescent and immunoperoxidase staining of frozen NALT sections were performed using anti-mucosal addressin cell adhesion molecule-1 (MAdCAM-1), anti-peripheral node addressin (PNAd), and anti-VCAM-1 mAbs. All NALT high endothelial venules (HEV) expressed PNAd, either associated with MAdCAM-1 or alone, whereas NALT follicular dendritic cells expressed both MAdCAM-1 and VCAM-1. These expression profiles were distinct from those of the gut mucosal inductive site, Peyer's patches (PP). The functionality of NALT HEV was determined using a Stamper-Woodruff ex vivo assay. The anti-L-selectin MEL-14 mAb blocked >90% of naive lymphocyte binding to NALT HEV, whereas the anti-MAdCAM-1 mAb, which blocks almost all naive lymphocyte binding to PP, minimally blocked binding to NALT HEV. NALT lymphocytes exhibited a unique L-selectin expression profile, differing from both PP and peripheral lymph nodes. Finally, NALT HEV were found in increased amounts in the B cell zones, unlike PP HEV. These results suggest that NALT is distinct from the intestinal PP, that initial naive lymphocyte binding to NALT HEV involves predominantly L-selectin and PNAd rather than alpha4beta7-MAdCAM-1 interactions, and that MAdCAM-1 and VCAM-1 expressed by NALT follicular dendritic cells may play an important role in lymphocyte recruitment and retention.     

Cutting edge: Uniqueness of lymphoid chemokine requirement for the initiation and maturation of nasopharynx-associated lymphoid tissue organogenesis

CD3(-)CD4(+)CD45(+) inducer cells are required for the initiation of mucosa-associated organogenesis of both nasopharynx-associated lymphoid tissues (NALT) and Peyer's patches (PP) in the aerodigestive tract. CXCL13(-/-) mice and mice carrying the paucity of lymph node T cell (plt) mutation and lacking expression of CCL19 and CCL21 accumulate CD3(-)CD4(+)CD45(+) cells at the site of NALT but not of PP genesis. Although NALT was observed to develop in adult CXCL13(-/-) and plt/plt mice, the formation of germinal centers in CXCL13(-/-) mice was affected, and their population of B cells was much lower than in the NALT of CXCL13(+/-) mice. Similarly, fewer T cells were observed in the NALT of plt/plt mice than in control mice. These findings indicate that the initiation of NALT organogenesis is independent of CXCL13, CCL19, and CCL21. However, the expression of these lymphoid chemokines is essential for the maturation of NALT microarchitecture.     

Role of CXC chemokine ligand 13, CC chemokine ligand (CCL) 19, and CCL21 in the organization and function of nasal-associated lymphoid tissue

Nasal-associated lymphoid tissue (NALT) orchestrates immune responses to Ags in the upper respiratory tract. Unlike other lymphoid organs, NALT develops independently of lymphotoxin-alpha (LTalpha). However, the structure and function of NALT are impaired in Ltalpha(-/-) mice, suggesting a link between LTalpha and chemokine expression. In this study we show that the expression of CXCL13, CCL19, CCL21, and CCL20 is impaired in the NALT of Ltalpha(-/-) mice. We also show that the NALT of Cxcl13(-/-) and plt/plt mice exhibits some, but not all, of the structural and functional defects observed in the NALT of Ltalpha(-/-) mice. Like the NALT of Ltalpha(-/-) mice, the NALT in Cxcl13(-/-) mice lacks follicular dendritic cells, BP3(+) stromal cells, and ERTR7(+) lymphoreticular cells. However, unlike the NALT of Ltalpha(-/-) mice, the NALT of Cxcl13(-/-) mice has peripheral node addressin(+) high endothelial venules (HEVs). In contrast, the NALT of plt/plt mice is nearly normal, with follicular dendritic cells, BP3(+) stromal cells, ERTR7(+) lymphoreticular cells, and peripheral node addressin(+) HEVs. Functionally, germinal center formation and switching to IgA are defective in the NALT of Ltalpha(-/-) and Cxcl13(-/-) mice. In contrast, CD8 T cell responses to influenza are impaired in Ltalpha(-/-) mice and plt/plt mice. Finally, the B and T cell defects in the NALT of Ltalpha(-/-) mice lead to delayed clearance of influenza from the nasal mucosa. Thus, the B and T cell defects in the NALT of Ltalpha(-/-) mice can be attributed to the impaired expression of CXCL13 and CCL19/CCL21, respectively, whereas impaired HEV development is directly due to the loss of LTalpha.     

Nonmucosal alphavirus vaccination stimulates a mucosal inductive environment in the peripheral draining lymph node

The strongest mucosal immune responses are induced following mucosal Ag delivery and processing in the mucosal lymphoid tissues, and much is known regarding the immunological parameters which regulate immune induction via this pathway. Recently, experimental systems have been identified in which mucosal immune responses are induced following nonmucosal Ag delivery. One such system, footpad delivery of Venezuelan equine encephalitis virus replicon particles (VRP), led to the local production of IgA Abs directed against both expressed and codelivered Ags at multiple mucosal surfaces in mice. In contrast to the mucosal delivery pathway, little is known regarding the lymphoid structures and immunological components that are responsible for mucosal immune induction following nonmucosal delivery. In this study, we have used footpad delivery of VRP to probe the constituents of this alternative pathway for mucosal immune induction. Following nonmucosal VRP delivery, J chain-containing, polymeric IgA Abs were detected in the peripheral draining lymph node (DLN), at a time before IgA detection at mucosal surfaces. Further analysis of the VRP DLN revealed up-regulated alpha4beta7 integrin expression on DLN B cells, expression of mucosal addressin cell adhesion molecule 1 on the DLN high endothelia venules, and production of IL-6 and CC chemokines, all characteristics of mucosal lymphoid tissues. Taken together, these results implicate the peripheral DLN as an integral component of an alternative pathway for mucosal immune induction. A further understanding of the critical immunological and viral components of this pathway may significantly improve both our knowledge of viral-induced immunity and the efficacy of viral-based vaccines.     

Regulation of mucosal dendritic cell function by receptor activator of NF-kappa B (RANK)/RANK ligand interactions: impact on tolerance induction

The mucosal immune system is uniquely equipped to discriminate between potentially invasive pathogens and innocuous food proteins. While the mechanisms responsible for induction of mucosal immunity vs tolerance are not yet fully delineated, recent studies have highlighted mucosal dendritic cells (DC) as being important in determining the fate of orally administered Ag. To further investigate the DC:T cell signals involved in regulating the homeostatic balance between mucosal immunity and tolerance, we have examined the expression and function of the TNFR family member receptor activator of NF-kappaB (RANK) and its cognate ligand, RANKL, in vitro and in vivo. Our data show that although DC isolated from mucosal lymphoid tissues expressed similar levels of surface RANK compared with DC isolated from peripheral lymphoid tissues, DC from the distinct anatomical sites displayed differential responsiveness to RANK engagement with soluble RANKL. Whereas splenic DC responded to RANKL stimulation with elevated IL-12 p40 mRNA expression, Peyer's patch DC instead preferentially displayed increased IL-10 mRNA expression. Our data also show that the in vivo functional capacity of mucosal DC can be modulated by RANKL. Treatment with RANKL in vivo at the time of oral administration of soluble OVA enhanced the induction of tolerance in two different mouse models. These studies underscore the functional differences between mucosal and peripheral DC and highlight a novel role for RANK/RANKL interactions during the induction of mucosal immune responses.     

Systemic Antibodies Can Inhibit Mouse Mammary Tumor Virus-Driven Superantigen Response in Mucosa-Associated Lymphoid Tissues

Many mucosal pathogens invade the host by initially infecting the organized mucosa-associated lymphoid tissue (o-MALT) such as Peyer’s patches or nasal cavity-associated lymphoid tissue (NALT) before spreading systemically. There is no clear demonstration that serum antibodies can prevent infections in o-MALT. We have tested this possibility by using the mouse mammary tumor virus (MMTV) as a model system. In peripheral lymph nodes or in Peyer’s patches or NALT, MMTV initially infects B lymphocytes, which as a consequence express a superantigen (SAg) activity. The SAg molecule induces the local activation of a subset of T cells within 6 days after MMTV infection. We report that similar levels of anti-SAg antibody (immunoglobulin G) in serum were potent inhibitors of the SAg-induced T-cell response both in peripheral lymph nodes and in Peyer’s patches or NALT. This result clearly demonstrates that systemic antibodies can gain access to Peyer’s patches or NALT.     

Sortase A Induces Th17-Mediated and Antibody-Independent Immunity to Heterologous Serotypes of Group A Streptococci

Group A streptococci (GAS) are associated with a variety of mucosal and invasive human infections. Recurrent infections by highly heterologous serotypes indicate that cross-serotype immunity is critical for prevention of GAS infections; however, mechanisms underlying serotype-independent protection are poorly understood. Here we report that intranasal vaccination of mice with Sortase A (SrtA), a conserved cell wall bound protein, reduced colonization of nasal-associated lymphoid tissue (NALT) by heterologous serotypes of GAS. Vaccination significantly increased CD4⁺ IL-17A⁺ cells in NALT and depletion of IL-17A by neutralizing antibody prevented GAS clearance from NALT which was dependent on immunization with SrtA. Vaccination also induced high levels of SrtA-specific antibodies; however, immunized, B cell-deficient mice cleared streptococcal challenges as efficiently as wild type mice, indicating that the cross-serotype protection is Th17-biased and antibody-independent. Furthermore, efficient GAS clearance from NALT was associated with a rapid neutrophil influx into NALT of immunized mice. These results suggest that serotype independent immune protection against GAS mucosal infection can be achieved by intranasal vaccination with SrtA and enhanced neutrophil function is critical for anti-GAS defense and might be a target for prevention of GAS infections.     

Vitamin A and vitamin D regulate the microbial complexity,barrier function,and the mucosal immune responses to ensure intestinal homeostasis

Diet is an important regulator of the gastrointestinal microbiota. Vitamin A and vitamin D deficiencies result in less diverse, dysbiotic microbial communities and increased susceptibility to infection or injury of the gastrointestinal tract. The vitamin A and vitamin D receptors are nuclear receptors expressed by the host, but not the microbiota. Vitamin A- and vitamin D-mediated regulation of the intestinal epithelium and mucosal immune cells underlies the effects of these nutrients on the microbiota. Vitamin A and vitamin D regulate the expression of tight junction proteins on intestinal epithelial cells that are critical for barrier function in the gut. Other shared functions of vitamin A and vitamin D include the support of innate lymphoid cells that produce IL-22, suppression of IFN-γ and IL-17 by T cells, and induction of regulatory T cells in the mucosal tissues. There are some unique functions of vitamin A and D; for example, vitamin A induces gut homing receptors on T cells, while vitamin D suppresses gut homing receptors on T cells. Together, vitamin A- and vitamin D-mediated regulation of the intestinal epithelium and mucosal immune system shape the microbial communities in the gut to maintain homeostasis.