Henrike L. Schieferdecker

γδ T cells in the human intestine express surface markers of activation and are preferentially located in the epithelium

We have investigated the expression of the alpha beta and the gamma delta T cell receptor (TCR) in the human intestine. By immunohistology we found that 39% of CD3+ intraepithelial lymphocytes (IEL) expressed the gamma delta TCR compared to 3% of CD3+ lamina propria lymphocytes (LPL). Cytofluorometric analysis of isolated cells revealed a significantly higher proportion of gamma delta T cells among CD3+ IEL compared to LPL and peripheral blood lymphocytes. This was due to an increase in both CD8+ (low density) and CD4-CD8- gamma delta T cells in IEL. Most alpha beta IEL expressed high-density CD8. About 30% of both IEL and LPL expressed CD25 (alpha-chain of the IL-2 receptor). HML-1 expression was detected on nearly all IEL and on 27% of LPL. CD25 and HML-1 were preferentially expressed on intestinal alpha beta and gamma delta T cells, respectively. Thus, human gamma delta T cells are located preferentially in the gut epithelium and are phenotypically different from alpha beta T cells, which constitute the majority of both LPL and IEL.

Immunological and trophical effects of Saccharomyces boulardii on the small intestine in healthy human volunteers.

Saccharomyces boulardii (S.b.) is used for the prevention and treatment of diarrhea of different etiologies. We prospectively investigated the effects of S.b. on lymphocytes and duodenal mucosa. Before and after oral administration of S.b. for 3 weeks, circulating and intestinal lymphocytes were isolated and characterized by flow cytometry. Trophic effects on duodenal mucosa were investigated by morphometry and determination of brush border enzyme activity. Results were compared intraindividually before and after S.b. In intestinal lymphocytes no phenotypic changes were observed. CD4+ cells of the peripheral blood had a significantly increased expression of CD25 (p < 0.02). None of twelve volunteers had an increase in villous surface area (n.s.). Immunoglobulin A content in small intestine secretion was unaltered. An increase in brush border enzyme activity of lactase, alpha-glucosidase, and alkaline phosphatase was observed (p < 0.01). Our findings indicate that S.b. has a positive effect on the maturation of enterocytes and only a minor influence on lymphocytes.

Phenotype and function of lamina propria T lymphocytes

Summary and ConclusionsLamina propria T cells have a low expression of the CD45RA antigen and a high expression of the CD45RO antigen. This phenotype is characteristic for memory T cells (table 2). In addition, T cells in the effector compartment of the mucosa bear surface antigens which are very rarely found in other sites of the immune system. Intestinal T cells also express functional IL-2 receptors and IL-2 receptor α chain mRNA, and are able to synthesize high amounts of IL-2. However, another marker of memory T cells, CD29, is not expressed in high density in the lamina propria indicating that lamina propria T cells differ from ‘classical’ memory T cells. This is supported by functional studies in nonhuman primates infected rectally withC. trachomatis which show that lamina propria T cells do not proliferate after stimulation with antigen but rather provide helper function for immunoglobulin synthesis (table 2).The intestinal lamina propria therefore contains highly specialized T cells which have a distinctive phenotype and are activated. Functionally these T cells can be characterized as differentiated effector lymphocytes which respond to triggering the antigen-specific T cell receptor by secreting helper factors for B cells. This concept is supported by recent studies showing that the pattern of lymphokines produced by lamina propria T cells and the responsiveness to certain lymphokines differ from those of other lymphocyte populations [25]. Lamina propria T cells thus represent a subset of memory T cells with a unique maturational state.

Special functional features of T-lymphocyte subpopulations in the effector compartment of the intestinal mucosa and their relation to mucosal transformation

Recent studies indicate that intestinal lamina propria T cells are highly specialized lymphocytes, which differ from T cells in other compartments of the immune system in several respects. In the present study phenotypic and functional characteristics of lamina propria T cells and their possible relation to mucosal growth will be discussed. Lymphocytes from human and nonhuman primate intestine were isolated by an enzymatic procedure. Lymphocytes were studied using dual-color immunofluorescence (FACS) and functional in vitro assays. CD4 positive (helper-) lamina propria T-cells lack the CD45RA antigen and express the CD45RO antigen. This phenotype is characteristic for memory T cells. In addition intestinal T cells express IL-2 receptors and IL-2 receptor mRNA, and are able to synthesize high amounts of IL-2. Functional studies in nonhuman primates infected rectally with Chlamydia trachomatis have shown that lamina propria T cells do not proliferate after stimulation with antigen but rather provide helper function for immunoglobulin synthesis. The intestinal lamina propria therefore contains highly specialized T cells which have the phenotype of memory T cells and which are activated. Functionally these T cells can be characterized as differentiated effector lymphocytes. Recent studies from other laboratories have shown that the pattern of lymphokines produced by lamina propria T cells and the responsiveness to certain lymphokines also differ from those of other lymphocyte populations. Since T-cell-derived lymphokines are also important regulators for epithelial growth and differentiation as well as for connective tissue metabolism, lamina propria T cells might be of major importance in mucosal growth and transformation.

Phenotype of HML-1-positive T cells in the human intestinal lamina propria.

ConclusionsIn conclusion, we did not find a strict correlation between the expression of HLM-1 and any of the investigated markers of naive and memory T cell function. Nevertheless, it has to be realized that the total lamina propria lymphocyte population did not show a phenotype absolutely correlating with ‘classical’ memory T cell markers. Even though lamina propria lymphocytes are almost exclusively CD45RA− and CD45R0+, only about 50% of the cells express CD29. Due to the increasing number of investigations on specialized T cell populations with various deviations from the typical naive/memory phenotype as defined by Sanders et al. [7, 8], one should perhaps define tissue-specific subsets of memory T cell populations. In this regard, HML-1+ cells might also represent a specialized ‘memory’ T cell population, which now has to be functionally characterized.

Phenotype of HML-1-positive and HML-1-negative T lymphocytes in the human intestinal lamina propria.

Intestinal lymphocytes encounter antigen in the afferent limb of the gut-associated lymphoid tissue (i.e. the Peyer’s Patches of the small intestine and the lymphoid follicles of the colon and rectum) and then recirculate to the efferent limb, comprising lymphocytes in the epithelium above the basement membrane (intraepithelial lymphocytes) and lymphocytes diffusely spread in the lamina propria (lamina propria lymphocytes, LPL). LPL thus are antigen-activated lymphocytes. In this regard they resemble the so-called memory cells, which differentiate from naive (or virgin) precursor cells upon antigenic stimulation. We therefore postulated that LPL might represent a tissue-specific subpopulation of memory cells.

The gamma/delta T cell receptor (TCR) is expressed on less than 50% of intraepithelial lymphocytes (IEL) in human intestine

The γ/δ T cell receptor (TCR) is found on virtually all intestinal intraepithelial cells (IEL) and on dendritic cells of the epidermis in the murine system but only on a small proportion of peripheral blood lymphocytes (PBL) or in other lymphoid organs; thus a specific function of γ/δ T cells at epithelial surfaces has been discussed [1]. Very limited data exists so far on the distribution and phenotypic characteristics of γ/δ T cells in the human intestine. Therefore, we studied the expression of the γ/δ TCR and the coexpression with other surface antigens on human intestinal IEL.

HML-1, an antibody raised against intestinal lymphocytes, recognises an antigen appearing on activated peripheral blood lymphocytes

The monoclonal antibody HML-1 [1] recognizes about 95% of intraepithelial lymphocytes and to a lower extent lamina propria lymphocytes (LPL) and mesenteric lymphoblasts. In order to characterize T cells expressing HML-1 in the lamina propria we investigated the number of HML-1 positive cells and their distribution on the T cell subsets CD4 and CD8. Since LPL are known to have an increased state of activation when compared to lymphocytes of other origin [2] we also investigated the in vitro inducibility of HML-1 on PBL.