Cytotoxic effector cell function in organized gut-associated lymphoid tissue (GALT)

Crosstalk Between Gut Microbiota and Innate Immunity and Its Implication in Autoimmune Diseases

The emerging concept of microbiota contributing to local mucosal homeostasis has fueled investigation into its specific role in immunology. Gut microbiota is mostly responsible for maintaining the balance between host defense and immune tolerance. Dysbiosis of gut microbiota has been shown to be related to various alterations of the immune system. This review focuses on the reciprocal relationship between gut microbiota and innate immunity compartment, with emphasis on gut-associated lymphoid tissue, innate lymphoid cells, and phagocytes. From a clinical perspective, the review gives a possible explanation of how the “gut microbiota—innate immunity” axis might contribute to the pathogenesis of autoimmune diseases like rheumatoid arthritis, spondyloarthritis, and systemic lupus erythematosus.

Activation of the superoxide-generating NADPH oxidase of intestinal lymphocytes produces highly reactive free radicals from sulfite

The objective of this study was to investigate the ability of immune cells of the small intestine to produce highly reactive free radicals from the food additive sulfites. These free radicals were characterized with a spin-trapping technique using the spin traps 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). In the presence of glucose, purified lymphocytes from intestinal Peyer's patches (PP) and mesenteric lymph nodes (MLN) were stimulated with phorbol 12-myristate 13-acetate (PMA) to produce superoxide and hydroxyl DEPMPO radical adducts. The formation of these adducts was inhibited by superoxide dismutase or diphenyleneiodonium chloride, indicating that these cells produced superoxide radical during reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation. With the treatment of sodium sulfite, PMA-stimulated PP lymphocytes produced a DEPMPO-sulfite radical adduct and an unknown radical adduct. When DEPMPO was replaced with DMPO, DMPO-sulfite and hydroxyl radical adducts were detected. The latter adduct resulted from DMPO oxidation by sulfate radical, which was capable of oxidizing formate or ethanol. Oxygen consumption rates were further increased after the addition of sulfite to PMA-stimulated lymphocytes, suggesting the presence of sulfiteperoxyl radical. Taken together, oxidants generated by stimulated lymphocytes oxidized sulfite to sulfite radical, which subsequently formed sulfiteperoxyl and sulfate radicals. The latter two radicals are highly reactive, contributing to increased oxidative stress, which may lead to sulfite toxicity, altered functions in intestinal lymphocytes, or both.

Human colonic mononuclear cells: studies of cytotoxic function

We isolated lymphocytes from the lamina propria of colon from 19 patients with inflammatory bowel disease, colon cancer, and certain benign conditions to determine: (1) if these lymphocytes could mediate mitogen-induced (MICC) and spontaneous cell-mediated cytotoxicity (SCMC), and (2) if there were any differences in cytotoxic effectiveness which could relate to the underlying disease. We found that lamina propria lymphocytes functioned well in MICC reactions with phytohaemagglutinin, but not concanavalin A as the inducing mitogen (specific lysis 28 5% vs 5 3%). Lamina propria lymphocytes did not mediate SCMC (specific lysis 0.3%). Neither the presence of inflammation not the underlying disease of the patient influenced the cytotoxic activity. Peripheral blood lymphocytes from normal subjects and patients performed well in MICC assay with both phytohaemagglutinin and concanvalin A as the inducing mitogen and were equally effective in SCMC reactions.

K-Cell activity in lamina proprial lymphocytes from the human colon

Using an enzymatic method for their isolation, it has been shown that human colonic lamina proprial lymphocytes, isolated from patients with various colonic diseases and depleted of polymorphonuclear leukocytes and macrophages, demonstrated K-cell activity in two antibody-dependent cell-mediated cytotoxicity assays in vitro. No differences were found between the activities of lamina proprial lymphocytes isolated from colonic specimens involved by Crohn's disease, chronic ulcerative colitis, or colonorectal carcinoma. K-cell activity was demonstrable using lymphoid cells isolated from the colons of patients receiving steroid therapy at the time of the therapeutic resections. These findings indicate the need for further investigation of possible roles for K-cells in local immune responses in the human bowel mucosa in inflammatory and neoplastic diseases.

Effects of sulfasalazine on selected lymphocyte subpopulations in vivo and in vitro

Sulfasalazine has proven to be an effective agent in the therapy of inflammatory bowel disease (IBD). Despite long and widespread usage, the mechanism of action of this drug is still not understood. Several investigators have suggested that the drug might act as an immunosuppressant. To examine this possibility, an in vivo study was undertaken to ascertain any quantitative change in the circulating T cells, Ig-bearing B cells, and complement receptor-bearing lymphocytes (CRL) of patients before and during therapy with sulfaslazine. Concomitant responses to skin test antigens were also evaluated. In vitro studies with control cells were performed to determine the influence of sulfasalazine and its components (sulfapyridine or 5-aminosalicylic acid) on the extent of antibody-dependent cellular cytotoxicity (ADCC), as well as on the number of T cells and CRL. Results indicate that neither sulfasalazine nor either of its components quantitatively alters those subpopulations of circulating mononuclear cells studied in vivo or in vitro--nor are these compounds responsible for any functional inhibition of ADCC.

Absence of K cells in human gut mucosa

Lymphocytes have been isolated from human rectal biopsies in numbers sufficient for microassay procedures. No antibody-dependent cell-mediated cytotoxic (ADCC) activity could be detected in normal or inflamed human gut mucosa, using two assay systems which detect predominantly K cell activity. The tissue localisation and circulation characteristics of K cells require definition before establishing their role as an efferent immunological mechanism.

Colostral cell-mediated immunity and the concept of a common secretory immune system

Historically colostrum and milk have been thought to confer immunity on the neonate only by virtue of their immunoglobulin content. Recently we have observed that colostrum also contains viable T lymphocytes capable of expressing cell-mediated immunity in vitro and have employed techniques of lymphocyte culture to elucidate the local nature of mammary tissue immunity at the T-cell level. The results indicate that the activity of colostral lymphocytes appears not to represent the total immunological experience of the mother but that they may contain reactive clones beneficial for the suckling. Colostral immunity appears to depend upon sensitizing events within the intestine and respiratory tract, followed by the migration of lymphoid precursors to the breast, suggesting a relationship between the expression of immunity at various secretory surfaces.