Oral—parenteral immunization leads to the appearance of IgG auto-anti-idiotypic cells in mucosal tissues

The appearance of plasma cells, specific for antigen or autologous idiotypic antibody, in rabbits immunized systemically, orally, or orally-systemically was determined using immunofluorescence techniques. Oral or parenteral immunizations alone did not lead to the appearance of anti-idiotypic cells in mucosal tissues, although IgA antigen-binding cells were observed in these sites after the oral administration of antigen. However, when rabbits were primed with orally administered antigen, followed by a regimen of concurrent oral—parenteral immunizations, IgG anti-idiotypic plasma cells were demonstrated in mucosal lymphoid tissues.     

Cellular and molecular mechanisms of internalization of mycobacteria by host cells

Mycobacteria are intracellular pathogens capable of invading mononuclear phagocytes, mucosal epithelial cells (including M cells) and Schwann cells. To enter cells, mycobacteria have been shown to interact with several molecules on macrophage and epithelial cell surfaces. This suggests adaptation to the host environment. In this review we address the strategies used by pathogenic mycobacteria to gain access to the intracellular environment.     

Evidence for a common mucosal immunologic system. I. Migration of B immunoblasts into intestinal, respiratory, and genital tissues.

The origins of immunoglobulin-containing cells in intestinal, respiratory, mammary, and genital tissues were studied in CBA/J female mice by using an adoptive lymphocyte transfer method. Within 24 hr after transfer, [3H]thymidine-labeled donor mesenteric lymph node (MLN) cells were observed in recipient gut, cervix and vagina, uterus, mammary glands, and MLN, where approximately 60% contained IgA and 25% IgG. In peripheral lymph nodes (PLN), 44% of the labeled cells after MLN transfer contained IgG, whereas only 8% were of the IgA isotype. The preference of the MLN to populate mucosal sites was clear from the results. Labeled PLN cells were transferred and the majority of these returned to their sites of origin and contained IgG. Of the small number of labeled PLN cells found in mucosal tissues, approximately equal percentages (30%) of IgA- anti IgG-containing cells were seen. Dividing cells prepared from mediastinal (bronchial) lymph nodes (BLN) showed a propensity to localize in the lungs rather than the intestine. However, the predominant immunoglobulin content of these donor cells in gut, lungs, and MLN was IgA. In recipient PLN, most labeled BLN cells contained IgG. These data support the concept of a common mucosal immunologic system.     

Perils at mucosal front lines for HIV and SIV and their hosts

HIV-1 and simian immunodeficiency virus (SIV), as well as their hosts, face perils at mucosal front lines in early infection. At these sites, 'resting' CD4+ memory T cells fuel infection (because they are hosts for virus), depleting CD4+ memory T cells throughout the lymphoid tissues, particularly in the gut, and eliciting an immunosuppressive regulatory T-cell response that impairs host defence. But HIV-1 and SIV also risk elimination at the earliest stage of infection, at the mucosal point of entry, if founder populations of infected cells do not expand sufficiently to establish a self-propagating infection. Microbicides and vaccines could increase these viral vulnerabilities at mucosal front lines.     

Bovine gamma delta T cell subsets express distinct patterns of chemokine responsiveness and adhesion molecules: a mechanism for tissue-specific gamma delta T cell subset accumulation

Subsets of gammadelta T cells localize to distinct tissue sites in the absence of exogenous Ag stimulation or development of effector/memory cells. Selective lymphocyte homing from the blood into tissues is controlled by a multistep process involving vascular and lymphocyte adhesion molecules, and G protein-linked chemokine receptors. The role of these mechanisms in the tissue tropism of gammadelta T cells is still poorly understood. In this study, we demonstrate that a subset of gammadelta T cells, most of which express an antigenically distinct TCR and are characterized by coexpression of CD8, selectively accumulated in tissues that expressed high levels of the mucosal vascular addressin, mucosal addressin cell adhesion molecule 1. These cells expressed higher levels of alpha(4)beta(7) integrins than other gammadelta T cell subsets and selectively migrated to the CCR7 ligand secondary lymphoid-tissue chemokine (CCL21). Integrin activation by CCL21 selectively increased CD8(+)gammadelta T cell binding to recombinant mucosal addressin cell adhesion molecule 1. These results suggest that the tropism of circulating CD8(+)gammadelta T cells for mucosal tissues is due, at least in part, to selective developmental expression of adhesion molecules and chemokine receptors.     

A common mucosal chemokine (mucosae-associated epithelial chemokine/CCL28) selectively attracts IgA plasmablasts

IgA immunoblasts can seed both intestinal and nonintestinal mucosal sites following localized mucosal immunization, an observation that has led to the concept of a common mucosal immune system. In this study, we demonstrate that the mucosae-associated epithelial chemokine, MEC (CCL28), which is expressed by epithelia in diverse mucosal tissues, is selectively chemotactic for IgA Ab-secreting cells (ASC): MEC attracts IgA- but not IgG- or IgM-producing ASC from both intestinal and nonintestinal lymphoid and effector tissues, including the intestines, lungs, and lymph nodes draining the bronchopulmonary tree and oral cavity. In contrast, the small intestinal chemokine, TECK (CCL25), attracts an overlapping subpopulation of IgA ASC concentrated in the small intestines and its draining lymphoid tissues. Surprisingly, T cells from mucosal sites fail to respond to MEC. These findings suggest a broad and unifying role for MEC in the physiology of the mucosal IgA immune system.     

Morphofunctional Organization of Lymphoepithelial Organs of the Human Pharynx

We present the current concepts of morphofunctional organization of the lymphoepithelial organs in the human pharynx based on the published data and authors" results. Functional compartmentation of palatine and pharyngeal tonsils is considered, which reflects cooperative cell interactions in the immune response; B- and T-areas have been structurally isolated and functionally substantiated. A special attention is paid to the fine structure of cryptal epithelium and its interactions with lymphoid cells infiltrating the epithelial sheet: lymphoepithelial symbiosis. Attention is also paid to structural homology of the lymphoepithelial compartment of palatine tonsils and thymus. The problem concerns the place of lymphoepithelial organs in hierarchy of the immune system as secondary organs with their own immunoregulatory area and having the functions of a regional center controlling the mucosal immunity.     

Transepithelial transport and mucosal defence II: secretion of IgA

In this second article on mucosal defence and transepithelial transport, Jean-Pierre Kraehenbuhl and Marian Neutra discuss the part played by a special class of antibody, polymeric IgA, in the protection of mucosal surfaces lining the digestive, respiratory and genital tracts, and the implications for mucosal vaccines. Polymeric IgA crosslinks luminal antigens or pathogens, thus preventing their interaction with epithelial cells. Following stimulation by antigen in the organized mucosal lymphoid tissue, effector B lymphocytes enter the circulation and migrate to distant mucosal or glandular sites, where they differentiate into polymeric-IgA-producing plasma cells. These antibodies reach the environment by transport across the epithelial cells of mucosal and glandular tissues.     

Immune- and enzyme histochemical characterisation of leukocyte populations within lymphoid and mucosal tissues of Atlantic halibut (Hippoglossus hippoglossus)

Leukocyte populations within the kidney, spleen, posterior intestine and gills of Atlantic halibut were investigated using a panel of histological, enzyme- and immunohistochemical methods. In the kidney and spleen, a diverse population of leukocytes was associated with the extensive network of sinusoids and larger blood vessels present in these tissues. IgM+ cells (B-cells, plasma cells and IgM-bearing macrophages) and large mononuclear cells showing reactivity for non-specific esterase (NSE) and acid phosphatase (ACP), representing macrophage populations, were often associated with vessel walls that were also the site of trapping of fluorescent microspheres. In the kidney, trapping of 0.1 and 0.5 microm diameter microspheres occurred at these sites but in the spleen, the 0.1 microm diameter microspheres were retained in ellipsoids. The lymphoid tissues of the kidney and spleen possessed a spread population of 5'-nucleotidase+ (5'N+) cells but compartmentalisation of the splenic white pulp was suggested by an absence of these 5'N+ reticular cells in areas associated with melanomacrophage accumulations and in areas rich in IgM+ cells. A striking feature of the mucosal tissues was the diversity of leukocyte populations within the epithelium particularly of the posterior intestine, including IgM+ cells and NSE+, ACP+ and 5'N+ mononuclear cells. Although limited in numbers in the posterior intestine, IgM+ cells were more common in the epithelium than in the lamina propria. In the gills, leukocytes as detected by enzymatic reactivity were scarce, but IgM+ cells were very abundant in the stratified epithelium of the gill arch and filaments. The difference in distribution of these leukocyte populations between the intestines and gills suggested a compartmentalisation of the mucosal immune system and the need to assess the immunological competence of mucosal tissues in Atlantic halibut.     

Flow cytometric characterization of the lymphocyte composition in a variety of mucosal tissues in healthy rhesus macaques

Background Rhesus monkeys play a central role in model studies on human infectious diseases, and often mucosal organs are affected by these pathogens, e.g. HIV. However, a comparative investigation into lymphocyte composition from different mucosal tissues is still missing. Methods Lymphocyte composition of duodenum, jejunum, ileum, colon, vagina, cervix, uterus and bronchoalveolar lavage from healthy rhesus monkeys was characterized in detail by flow cytometry. Moreover, we compared the lymphocyte proportions from intestinal biopsies with resections. Results All mucosal tissues exhibited higher values of CD8⁺, CD4⁺ CCR5⁺ and CD45RA^? memory T cells than blood, but similar levels of total T cells. Especially within the four gut sites, the lymphocyte composition varied significantly. The relative proportions of lymphocyte subsets from duodenal and colonic biopsies compared to resections differed. Conclusion The lymphocyte composition highly varies between different mucosal sites, and data obtained from biopsy and necropsy samples were mostly not comparable.     

Heterogeneity of the simian immunodeficiency virus (SIV) specific CD8(+) T-cell response in mucosal tissues during SIV primary infection

Virus-specific CD8(+) T cells play an important role in controlling viral replication during acute primary infection. At this early stage, mucosal tissues represent a major site of viral replication. Therefore, the presence of functional virus-specific CD8(+) effector T cells in the mucosa during primary infection is a key issue in the pathogenesis of infection. In order to evaluate the extent of this response, six rhesus macaques were infected with simian immunodeficiency virus (SIV)mac251 and sacrificed on day 28 following infection. The functional activity of SIV-effector CD8(+) T cells was evaluated by means of a gamma-IFN ELISpot assay with autologous cells expressing SIV env, gag, pol and nef genes as antigen-presenting cells. This evaluation was performed on PBMCs, spleen, peripheral lymph node, gut-associated lymph node and lamina propria lymphocytes isolated from different mucosal sites. In parallel, the cell-associated viral load was quantified in all these tissues. Five macaques had gamma-IFN SIV-specific CD8(+) T cells in PBMCs and/or lymph nodes. However, in these macaques, these CD8(+) T cells were only present in seven mucosal sites out of 24 tested (the lamina propria lymphocytes of the duodenum, jejunum, ileum and colon were evaluated separately for each animal), whereas they were detected in all corresponding gut-associated lymph nodes. In addition, the mean frequency of SIV-specific gamma-IFN-secreting CD8(+) T cells was 117 +/- 228 per 10(6) cells in the lamina propria vs. 958 +/- 1184 in gut associated lymph nodes (P = 0.001). No overall correlation was observed between the CD8(+) T-cell activity and the viral load: among the 17 mucosal sites in which the virus was isolated, no specific activity was detected in 13 sites. In conclusion, these data indicate that the frequencies of SIV-specific gamma-IFN-secreting CD8(+) T cells are low in the mucosa during early primary infection. This may be of importance with regard to the intense viral replication observed in the mucosa at this stage.     

Gut- and bronchus-associated lymphoid tissue

Bronchus-associated and gut-associated lymphoid tissues (BALT and GALT) have both functional and morphologic similarities and are involved in seeding lung, gut, and other mucosal sites with predominantly IgA-containing B cells. Both types of lymphoid tissue are engaged in the regulation and the controlled amplification of immune responses, which vary from positive mucosal responses in both mucosae and peripheral tissues to local mucosal responses and systemic tolerance. Their further involvement in provision of cells destined to reside in the epithelial compartment of the body appears likely but requires further investigation. Their role in the provision of precursors of mucosal mast cells must also be explored further, but some participation in this event appears likely. The mucosa-associated lymphoid tissue (MALT) system appears to be integrated with the systemic immune system but may be considered as separate from it in several functional ways.     

Both mucosal and systemic routes of immunization with the live,attenuated NYVAC/simian immunodeficiency virus SIV(gpe) recombinant vaccine result in gag-specific CD8(+) T-cell responses in mucosal tissues of macaques

As most human immunodeficiency virus (HIV) infection occurs via mucosal surfaces, an important goal of vaccination may be the induction of virus-specific immune responses at mucosal sites to contain viral infection early on. Here we designed a study in macaques carrying the major histocompatibility complex class I Mamu-A(*)01 molecule to assess the capacity of the highly attenuated poxvirus NYVAC/simian immunodeficiency virus (SIV) SIV(gpe) vaccine candidate administered by the intranasal, intramuscular, or intrarectal route to induce mucosal immunity. All macaques, including one naive macaque, were exposed to SIV(mac251) by the intrarectal route and sacrificed 48 h after infection. The kinetics of immune response at various time points following immunization with NYVAC/SIV(gpe) and the anamnestic response to SIV(mac251) at 48 h after challenge were assessed in blood, in serial rectal and vaginal biopsy samples, and in tissues at euthanasia with an SIV(mac) Gag-specific tetramer. In addition, at euthanasia, antigen-specific cells producing gamma interferon or tumor necrosis factor alpha from the jejunum lamina propria were quantified in all macaques. Surprisingly, antigen-specific CD8(+) T cells were found in the mucosal tissues of all immunized macaques regardless of whether the vaccine was administered by a mucosal route (intranasal or intrarectal) or systemically. In addition, following mucosal SIV(mac251) challenge, antigen-specific responses were mainly confined to mucosal tissues, again regardless of the route of immunization. We conclude that immunization with a live vector vaccine results in the appearance of CD8(+) T-cell responses at mucosal sites even when the vaccine is delivered by nonmucosal routes.     

Systemic vaccination prevents the total destruction of mucosal CD4 T cells during acute SIV challenge

BACKGROUND: Acute human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) infections are accompanied by a systemic loss of memory CD4 T cells, with mucosal sites serving as a major site for viral replication, dissemination and CD4 T cell depletion. Protecting the mucosal CD4 T cell compartment thus is critical to contain HIV, and preserve the integrity of the mucosal immune system. The primary objective of this study was to determine if systemic vaccination with DNA/rAd-5 encoding SIV-mac239-env, gag and pol could prevent the destruction of CD4 T cells in mucosal tissues. METHODS: Rhesus macaques were immunized with DNA/r-Ad-5 encoding SIV genes and compared with those immunized with sham vectors following high dose intravenous challenge with SIVmac251. SIV specific CD4 and CD8 T cell responses, cell associated viral loads and mucosal CD4 T cell dynamics were evaluated. RESULTS: Strong SIV specific immune responses were induced in mucosal tissues of vaccinated animals as compared with sham controls. These responses expanded rapidly following challenge suggesting a strong anamnestic response. Immune responses were associated with a decrease in cell associated viral loads, and a loss of fewer mucosal CD4 T cells. Approximately 25% of mucosal CD4 T cells were preserved in vaccinated animals as compared with <5% in sham controls. These results demonstrate that systemic immunization strategies can induce immune responses in mucosal tissues that can protect mucosal CD4 T cells from complete destruction following challenge. CONCLUSIONS: Preservation of mucosal CD4 T cells can contribute to maintaining immune competence in mucosal tissues and provide a substantial immune benefit to the vaccinees.     

Nutrient tasting and signaling mechanisms in the gut V. Mechanisms of immunologic sensation of intestinal contents

Immune perception of intestinal contents reflects a functional dualism with systemic hyporesponsiveness to dietary antigens and resident microflora (oral tolerance) and active immune responses to mucosal pathogens. This facilitates optimal absorption of dietary nutrients while conserving immunologic resources for episodic pathogenic challenge. Discrimination between dangerous and harmless antigens within the enteric lumen requires continual sampling of the microenvironment by multiple potential pathways, innate and adaptive recognition mechanisms, bidirectional lymphoepithelial signaling, and rigorous control of effector responses. Errors in these processes disrupt mucosal homeostasis and are associated with food hypersensitivity and mucosal inflammation. Mechanisms of mucosal immune perception and handling of dietary proteins and other antigens have several practical and theoretical implications including vaccine design, therapy of systemic autoimmunity, and alteration of enteric flora with probiotics.     

Mucosal immunity and vaccination

Abstract The gut mucosal immune system is a critical component of the body's defense against pathogenic organisms, especially those responsible for enteric infections associated with diarrhoeal disease. Attempts to vaccinate against infections of mucosal tissues have been less successful than vaccination against systematic infections, to a large extent reflecting a still incomplete knowledge about the most efficient means for inducing protective local immune responses at these sites. Secretory IgA (SIgA) is the predominating immunoglobulin along mucosal surfaces, and SIgA antibodies generated in gastrointestinal, respiratory or genito-urinary mucosal tissues can confer protection against infections affecting or originating in these sites. An efficacious intestinal SIgA immunity-inducing oral vaccine against cholera has been developed recently, and development of oral vaccines against other enteric infections such as those caused by enterotoxigenic Escherichia coli, Shigella and rotaviruses is in progress as well. Based on the concept of a common mucosal immune system through which activated lymphocytes from the gut can disseminate immunity to other mucosal and glandular tissues, there is currently also much interest in the possibility of developing oral vaccines against infections in the respiratory and urogenital tracts. However, the large and repeated antigen doses often required to achieve a protective immune response still makes this vaccination approach impractical for many purified antigens. There is, therefore, a great need to develop strategies for enhancing delivery of antigen to the mucosal immune system as well as to identify mucosa-active immunostimulating agents (adjuvants). These and other aspects of mucosal immunity in relation to immunization and vaccine development are discussed in this short review article.     

Mucosal immunity and vaccination.

The gut mucosal immune system is a critical component of the body's defense against pathogenic organisms, especially those responsible for enteric infections associated with diarrhoeal disease. Attempts to vaccinate against infections of mucosal tissues have been less successful than vaccination against systemic infections, to a large extent reflecting a still incomplete knowledge about the most efficient means for inducing protective local immune responses at these sites. Secretory IgA (SIgA) is the predominating immunoglobulin along mucosal surfaces, and SIgA antibodies generated in gastrointestinal, respiratory or genito-urinary mucosal tissues can confer protection against infections affecting or originating in these sites. An efficacious intestinal SIgA immunity-inducing oral vaccine against cholera has been developed recently, and development of oral vaccines against other enteric infections such as those caused by enterotoxigenic Escherichia coli, Shigella and rotaviruses is in progress as well. Based on the concept of a common mucosal immune system through which activated lymphocytes from the gut can disseminate immunity to other mucosal and glandular tissues, there is currently also much interest in the possibility of developing oral vaccines against infections in the respiratory and urogenital tracts. However, the large and repeated antigen doses often required to achieve a protective immune response still makes this vaccination approach impractical for many purified antigens. There is, therefore, a great need to develop strategies for enhancing delivery of antigen to the mucosal immune system as well as to identify mucosa-active immunostimulating agents (adjuvants). These and other aspects of mucosal immunity in relation to immunization and vaccine development are discussed in this short review article.     

M-cells: origin, morphology and role in mucosal immunity and microbial pathogenesis

M-cells are specialized cells found in the follicle-associated epithelium of intestinal Peyer's patches of gut-associated lymphoid tissue and in isolated lymphoid follicles, appendix and in mucosal-associated lymphoid tissue sites outside the gastrointestinal tract. In the gastrointestinal tract, M-cells play an important role in transport of antigen from the lumen of the small intestine to mucosal lymphoid tissues, where processing and initiation of immune responses occur. Thus, M-cells act as gateways to the mucosal immune system and this function has been exploited by many invading pathogens. Understanding the mechanism by which M-cells sample antigen will inform the design of oral vaccines with improved efficacy in priming mucosal and systemic immune responses. In this review, the origin and morphology of M-cells, and their role in mucosal immunity and pathogenesis of infections are discussed.