T cell and mononuclear phagocyte populations of the human small and large intestine

Experimental mucosal disease in cattle: changes in the number of lymphocytes and plasma cells in the mucosa of the small and large intestine

Changes in the number of lymphocyte and plasma cell subtypes were investigated in the lamina propria and in the epithelium of the small and large intestine of cattle with mucosal disease. Mucosal disease had been induced experimentally in seven out of 13 animals persistently viremic with non cytopathogenic BVD-virus by inoculation with a matching cytopathogenic BVD-virus. For comparison, six clinically healthy, persistently viremic cattle were used. IgA+, IgM+ and IgG1+ plasma cells, BoCD4+, BoCD8+ and gamma delta + T-lymphocytes, and the antigen of the cytopathogenic BVD-virus were demonstrated in tissue sections by immunohistochemistry. Distribution of cellular subtypes in the controls was consistent with data reported from non infected cattle. In cattle with mucosal disease, a decrease in the number of plasma cells which was significant for IgA+ and IgM+, but not for IgG1+ plasma cells was found in the lamina propria. The number of BoCD4+ T-lymphocytes was reduced in the small intestine, whereas their number per mm2 of mucosa was increased in the large intestine. Numbers of intraepithelial BoCD8+ and gamma delta + T-lymphocytes were severely decreased. Antigen of the cytopathogenic BVD-virus was detected predominantly in epithelial cells of the crypts. Overall there is a severe loss of effector cells which are essential components of the humoral and cell mediated immune protection of the mucosal barrier. The decrease of immunoregulatory cells in the lamina propria and epithelium may contribute to the transformation of mucosal architecture in mucosal disease.

Spondylarthropathies: from gut to target organs

Recent studies strongly support the concept that gut and joint inflammation are closely related. Progress also has been made in identifying individual mechanisms that contribute to the pathogenesis of joint disease in IBD and in undifferentiated SpAs. However, the interrelationship of these mechanisms that result in chronic disease manifestations at a site distant from the initiating event remain to be elucidated. The local absence of homing molecule receptors in the gut wall combined with an expression of these receptors in target organs can be responsible for the transformation of the synovial membrane and/or the enthesis into an aberrant tertiary lymphoid organ of the gut.

Intestinal intraepithelial lymphocytes and lymphoepithelial interactions in the human gastrointestinal mucosa

Although representing a major immunological apparatus, it is not known how the immune system of the intestinal mucosa differentiates between dietary antigens (resulting in systemic tolerance) and potential pathogens. It is thought that intraepithelial T lymphocytes (IEL) may play a central role in local intestinal immunity and are likely to be important in immunity to gastrointestinal neoplasms and rejection responses to gut allografts. However, the biology of IEL and their unusual immunological microenvironments in the gastrointestinal mucosa are little understood. IEL are predominantly CD8+ TcR alpha beta+ CD3+ T cells which differ from lamina propria and peripheral T cells in many respects. IEL show low expression of CD5, CD6, LFA-1 (CD11a/CD18) and VLA-4, and high expression of HML-1. TcR gamma delta + IEL, although a minority population, are also phenotypically distinct, insofar as they are 50% CD8+, mainly V delta 1+ V gamma 9- and CD4- CD5-. IEL show poor proliferative responses to PHA, anti-CD3 and phorbol ester/calcium ionophore in vitro and have no clear functional role: they neither provide helper nor suppressor functions for Ig synthesis by B cells and do not mediate spontaneous cytotoxicity. However, there is evidence that IEL show preferential activation in response to sheep erythrocytes, presumably signalling via CD2. As normal and inflamed intestinal epithelia do not express ICAM-1, it seems unlikely that the LFA-1/ICAM-1 interaction is of importance to IEL activation. Rather, the CD2 (LFA-2) interaction with LFA-3 expressed by enterocytes may serve both to anchor IEL and to provide an accessory stimulus for activation. Nevertheless, the questions of antigenic specificity and immunological role remain unanswered.

Immunoregulatory functions for murine intraepithelial lymphocytes: gamma/delta T cell receptor-positive (TCR+) T cells abrogate oral tolerance, while alpha/beta TCR+ T cells provide B cell help

Past work has shown that a subset of effector T cells with unique characteristics could abrogate hapten- or antigen-induced tolerance, and the reconstitution of this immune response has been termed contrasuppression. We have studied contrasuppression in a model of oral tolerance (OT) in which adoptively transferred antigen-specific T contrasuppressor (Tcs) cells reverse OT and result in antibody responses to the eliciting antigen. In the present study, we show that murine intraepithelial lymphocytes (IELs) from mice orally immunized with sheep red blood cells (SRBC) contain T cells that exhibit Tcs cell activity. This effect was mediated by CD3+ gamma/delta T cell receptor-positive (TCR+), but not alpha/beta TCR+ T cells, and gamma/delta TCR+ Tcs cells were associated with both the CD4-,CD8+ and CD4-,CD8- (double-negative) IEL fractions. The CD4-,CD8+ gamma/delta TCR+ IELs were further separated into Vicia villosa-adherent and -nonadherent fractions. Adoptive transfer of V. villosa-adherent gamma/delta TCR+ T cells to mice with OT to SRBC resulted in splenic IgA, IgM, and IgG subclass anti-SRBC responses, while V. villosa-nonadherent gamma/delta TCR+ T cells were without activity. The gamma/delta TCR+ IELs did not support in vitro antibody responses in B cell cultures, while alpha/beta TCR+ IELs were effective T helper cells. Further, cytokine production by the gamma/delta TCR+ IELs was examined, and the gamma/delta TCR+ V. villosa-adherent fraction, which possessed contrasuppressor function, contained low levels of IL-5 mRNA and small numbers of IL-5-producing cells when compared with alpha/beta TCR+ IELs and V. villosa-nonadherent gamma/delta TCR+ IELs. Our results now show that mouse IELs contain two distinct types of T cells that function in the immune response, e.g., alpha/beta TCR+ T cells that produce IL-5 and function as helper cells, and gamma/delta TCR+ T cells that restore antibody responses in mice that had been orally tolerized with antigen.

Human colonic intra-epithelial lymphocytes are suppressor cells

Human colonic intra-epithelial lymphocytes (IEL) suppress the proliferation of autologous lamina propria lymphocytes, but not autologous peripheral blood mononuclear cells, when stimulated with phytohaemagglutinin. This suppressor function is mediated by a CD8-dependent soluble factor and is not related to the expression of the gamma delta T cell receptor. These findings may be relevant to the induction of mucosal tolerance. However, there is no defect in suppressor activity of colonic IEL in inflammatory bowel disease.

Expression of leukocyte adhesion molecules by mucosal mononuclear phagocytes in inflammatory bowel disease

Leukocyte adhesion molecules are important in cell-cell interactions of the immune system. Lymphocyte function-associated antigen 1 (cluster designation 11a) mediates interactions between T cells and mononuclear phagocytes through its ligand, the intercellular adhesion molecule 1 (CD54), whereas complement receptors 3 (CD 11b) and 4 (CD11c) are involved in complement-mediated phagocytosis. Expression of CD11 molecules and intercellular adhesion molecule 1 was studied in colonic biopsy specimens from 20 patients with inflammatory bowel disease and 10 normal controls. In normal colon, few mononuclear phagocytes expressed lymphocyte function-associated antigen 1 and intercellular adhesion molecule 1 at high densities. The major adhesion molecule was CD11c. Thus, the largest population of normal colonic mononuclear phagocytes was represented by quiescent, resident macrophages with likely phagocytic function. In inflammatory bowel disease, mononuclear phagocytes showed only a slight increase in CD11a expression and no significant change in expression of CD11b and CD11c. By contrast, the percentage of mononuclear phagocytes expressing intercellular adhesion molecule 1 was increased from 6.9% +/- 3.9% in controls to 69.2% +/- 12.8% in ulcerative colitis (P less than 0.001) and to 45.7% +/- 22.8% in Crohn's disease (P less than 0.01), showing a close relationship with histological activity. The increased expression of intercellular adhesion molecule 1 in inflammatory bowel disease indicates a state of immunological activation induced by local release of inflammatory cytokines. Such induction of intercellular adhesion molecule 1 on mononuclear phagocytes may be important in the maintenance of chronic inflammation by facilitating interactions with T cells and T-cell antigen recognition.

Colonic mucosal T lymphocytes in ulcerative colitis: expression of CD7 antigen in relation to MHC class II (HLA-D) antigens

T-cell subsets and their activation state were examined by double-label immunofluorescence of cryostat tissue sections of the colon from 21 patients with ulcerative colitis (UC) and 30 histologically normal controls. Expression of MHC class I (HLA-A, B, C) and class II (HLA-D) antigens was studied in parallel. In the normal colonic mucosa, the CD4:CD8 ratio in the epithelial compartment approximated 1:1, and in the lamina propria, 2.55:1. Of the CD8+ (cytotoxic/suppressor) subset, approximately half did not express the CD5 "pan-T" marker in either compartment. Virtually no Leu8+ cells were observed, implying that the CD4+ subset consisted of helper, rather than suppressor-inducer cells. Classical markers of T-cell activation (CD25, HLA-D) and proliferation were absent, and strong expression of the CD7 "immunostimulation" marker was approximately equal in both CD4 and CD8 subsets. The epithelium was uniformly negative for class II antigens, but positive for class I. In UC, there were no significant alterations in CD4:CD8 ratios in either compartment, and there were no changes with respect to phenotype of the subsets. In 11 of 19 patients (mainly with total colitis), enterocytes were HLA-D+. In this HLA-D+ group, there was an increase in the percentage of CD4+ cells coexpressing CD7; this difference was significant (P less than 0.02) in the lamina propria. Increased expression of CD7 was also found by the CD6+ T cell subset (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphoepithelial interactions in the mucosal immune system

Images