Dietary plasma proteins, the intestinal immune system, and the barrier functions of the intestinal mucosa1

Effects of spray-dried bovine plasma protein in milk replacers fed at a high plane of nutrition on performance, intestinal permeability, and morbidity of Holstein calves

The largest pool of macrophages in the body is harboured by the intestinal mucosa. As the principal phagocytic component of the immune system, macrophages are essential for maintaining mucosal homeostasis as they prevent commensal bacteria from adhering to mucosal epithelial cells. This study provides a RAM11 immunohistochemical and electron microscopic investigation of the existence, localization and distribution of intestinal macrophages in organized gut-associated lymphoid tissue (GALT), including Peyer's patches (PPs), the sacculus rotundus (SR) and the appendix, in the Angora rabbit. Although rabbit intestinal macrophages did not express the tissue macrophage marker macrosialin (CD68), they expressed RAM11. RAM11-positive intestinal macrophages were mostly localized to the subepithelial dome region, interfollicular area and germinal centres (GCs) of the GALT and the lamina propria or submucosa of the ileum and jejunum devoid of PPs and were also observed in the follicle-associated epithelium of PPs, but not in that of the SR and appendix. RAM11-positive macrophages containing engulfed apoptotic bodies were present in the GCs of the lymphoid follicles in the GALT. Electron microscopy further revealed multiple macrophages containing apoptotic bodies within the GCs of the follicles in the GALT. Some macrophage aggregations were observed in the GC and between the GC and the corona region of the follicles in the SR and appendix. Rabbit intestinal macrophages thus undertake both potent phagocytic activity and the efficient scavenging of apoptotic cells. Immunohistochemical data suggest that RAM11 can be reliably used for the determination of intestinal macrophages in the GALT of rabbits.

8 Immunology of gastrointestinal lymphoma

4. Gastrointestinal mucosal immunity

The immunoregulatory effects of dietary alpha-tocopherol (Toc) and tocotrienols (T-3) on humoral and cell-mediated immunity and cytokine productions were examined in Brown Norway rats. We found that the IgA and IgG productivity of spleen and mesenteric lymph node (MLN) lymphocytes was significantly enhanced in the rats fed on Toc or T-3, irrespective of concanavalin A (Con A) stimulation of the lymphocytes. On the contrary, the IgE productivity of lymphocytes from the rats fed on Toc or T-3 was less without Con A stimulation, but was greater in the presence of Con A, especially in the T-3 group. Toc or T-3 feeding significantly decreased the proportion of CD4+ T cells and the ratio of CD4+/CD8+ in both spleen and MLN lymphocytes of the rats fed on Toc or T-3. The interferon-gamma productivity of MLN lymphocytes was higher in the rats fed on Toc or T-3 than in those fed on a control diet in the presence of Con A, while that of spleen lymphocytes was lower in the rats fed on Toc or T-3. In addition, T-3 feeding decreased the productivity of tumor necrosis factor-alpha of spleen lymphocytes, while it enhanced the productivity of MLN lymphocytes. These results suggest that oral administration of Toc and T-3 affects the proliferation and function of spleen and MLN lymphocytes.

Oral administration of muramyl dipeptide into mice modulates cell proliferation, immunoglobulin synthesis and cytokine mRNA levels in gut associated lymphoid tissues

Cordyceps sinensis, one of the well-known fungi used in traditional Chinese medicine, is recognized to play a role in the metabolic process of inflammation and immunity. The purpose of this study was to evaluate the effects of water extracts of C. sinensis on the immune function of mesenteric lymph node (MLN) lymphocytes in C57Bl/6N mice. C. sinensis-treated mice were administered the respective extract by oral gavage for 4 weeks. Immunoglobulin E concentrations in serum and MLN lymphocytes were significantly lower in C. sinensis-treated mice than in control mice. In contrast, the immunoglobulin A concentration from the C. sinensis group was higher than that in control mice. C. sinensis increased the proportion of CD4(+) and CD8(+) T cells in MLN lymphocytes. C. sinensis significantly decreased interleukin-4 and interleukin-10 cytokine concentrations. Therefore, water extracts of C. sinensis modulate immune parameters through regulation of immunoglobulin production resulting from decreased T-lymphocyte helper 2 cytokine secretion and reduce cytokine secretion in MLN lymphocytes.

Predominance of helper-inducer T cells in mesenteric lymph nodes and intestinal lamina propria of normal nonhuman primates

In species other than mouse, little is known about the origin and development of marginal zone (MZ) B cells. Using cross-reactive antibodies, we identified and characterized splenic MZ B cells in rabbits as CD27(+) CD23(-). In rabbits in which organized gut-associated lymphoid tissue (GALT) was surgically removed at birth, we found only CD23(+) follicular (FO) B cells and almost no CD27(+) MZ B cells in the spleen, indicating that GALT is required for the development of splenic MZ B cells. These findings lead us to suggest that commensal microbiota contribute to the development of MZ B cells.

In this study, we investigated the effect of morphine on the mucosal immune system using fragment cultures of ileal segments, Peyer's patches (PPs), and mesenteric lymph nodes. Mice were implanted s.c. with a morphine slow release pellet. Control groups received a naltrexone slow release pellet, a placebo pellet, or both a morphine and a naltrexone pellet. After 48 h, mice were orally immunized with cholera toxin (CT) and were boosted orally 1 wk later. Animals were sacrificed 1 wk after the booster immunization, and PPs, mesenteric lymph nodes, and ileal segments were cultured in 24-well plates for 12 days. Morphine resulted in a highly significant inhibition of CT-specific IgA and IgG production in fragment culture supernatants of all three tissues compared with placebo. Naltrexone blocked the reduction in Ab levels induced by morphine, indicating that the effect is opioid receptor mediated. Morphine did not significantly alter total IgA levels in any of the tissue culture supernatants. Morphine also inhibited CT-specific IgA and IgG levels in serum. By flow cytometry, morphine did not alter the lymphoid cell composition in PPs compared with placebo. The effect of morphine on TGF-beta, IL-5, and IL-6 mRNA expression in PPs and ileal segments was determined following oral immunization with CT. Morphine significantly decreased TGF-beta mRNA compared with that in the placebo group, and naltrexone blocked this effect. These results indicate that morphine inhibits Ag-specific IgA responses in gut-associated lymphoid tissue at least partially through the inhibition of TGF-beta, a putative IgA switch factor, in the gastrointestinal tract.

Our previous studies indicated that cloned T cells obtained from Peyer's patches (PP) (Lyt-1+, 2-, Ia+, and H-2K/D+) evoked immunoglobulin (Ig) class switching of PP B cells from sIgM to sIgA cells in vitro; however, these switch T cells could not in themselves provide optimal help for the differentiation of postswitch sIgA-bearing PP B cells to IgA-secreting cells. Thus, in the present report we described studies focused on mechanisms regulating terminal differentiation of the postswitch PP sIgA-bearing B cells. First, to explore the effect of T cell-derived B cell differentiation factor(s) (BCDF) and macrophage factor(s) (MF) on the terminal maturation of PP B cells, LPS-stimulated PP B cells were co-cultured for 7 d with cloned T cells in the presence or absence of the above factors. In the absence of PP cloned T cells the BCDF and MF had only a modest effect on IgA production, whereas in the presence of PP, but not spleen cloned T cells, IgA production was increased. Next, to investigate the effect of T cells derived from a gut-associated lymphoid tissue (GALT), mesenteric lymph nodes (MLN), as well as from spleen on terminal differentiation of postswitch sIgA PP B cells, LPS-driven PP B cells were precultured with the cloned T cells to induce a switch to sIgA, and subsequently cultured with MLN or spleen T cells or a Lyt-2+- depleted T cell subset in the presence of a T-dependent polyclonal mitogen, staphylococcal protein A. Alternatively, in the second culture period BCDF alone was added, instead of T cells and protein A. Here it was found that B cells pre-exposed to switch T cells from PP, but not spleen, were induced to produce greatly increased amounts of IgA in the presence of protein A and T cells or a Lyt-2+-depleted T cell subset as well as in the presence of BCDF alone. Furthermore, in the presence of BCDF alone many B cells expressed cytoplasmic IgA. These observations strongly support the view that the terminal differentiation of postswitch sIgA B cells is governed by helper T cells and macrophages, or factors derived from such cells. Such cells or factors do not affect preswitch B cells.

The Post-Natal Development of Lymph Nodes in Mice

Apoptosis of antigen-specific CTLs contributes to low immune response in gut-associated lymphoid tissue post vaccination

The effects of hypophysectomy on the immune response in mice orally immunized with sheep red blood cells (SRBC) was investigated. Hypophysectomized and sham-operated animals display elevated serum levels of SRBC-specific IgG. In addition, splenic lymphocytes obtained from hypophysectomized mice (i) exhibit an enhanced blastogenic response to SRBC, (ii) present with a lower frequency of T (thy 1.2+) cells and produce more total IgG polyclonal antibody in culture in comparison to splenic lymphocytes obtained from non-operated (control) mice. Peyer's patch (PP) and mesenteric lymph node (MLN) lymphocytes from hypophysectomized animals secreted elevated levels of total IgG compared to saline-treated controls. The culture supernates of splenic lymphocytes obtained from hypophysectomized, sham-operated, and control animals contain interleukin-2 suppressive factors as determined using the CTLL-2 cell line. The suppressive effect mediated by the lymphocyte culture supernates is less apparent on interleukin-4-mediated CTLL-2 proliferation. The culture supernates from PP lymphocytes obtained from hypophysectomized mice contain potent interleukin-2 suppressive factors while PP lymphocyte culture supernates from sham-operated and control mice displayed no suppressive activity. Likewise, culture supernates from MLN lymphocytes of hypophysectomized, sham-operated, and control mice possessed no suppressive factors for interleukin-2- or interleukin-4-mediated CTLL-2 proliferation. Taken together, the identification of suppressive factors in the lymphocyte culture supernates along with the enhanced blastogenic response and serum anti-SRBC IgG levels in hypophysectomized mice suggests neuroendocrine pathways regulate oral-induced tolerance.

The in vivo antibody response in rat gut-associated lymphoid tissue (GALT) after immunization with bacterial polysaccharide antigen