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Despite the variation in results of studies on isolated intestinal mucosal T cells obtained in different laboratories, it can be said that: 1) T lymphocytes and their subsets can be isolated from normal and from diseased intestinal mucosa. 2) Most of the functions of these T cells are, as far as has been studied, similar to those of peripheral blood T tions of T lymphocytes and the different distribution of these antigens between intestinal epithelium, which normally shows strong expression of HLA-A,B,C antigens but weak or no expression of HLA-DR antigens, and the lamina propria, which contains large numbers of histiocytic cells which are rich in HLA-DR antigens, may be vital to the functions of intestinal T cells. Removal of cells from the close association with these antigens may therefore alter their functions. Secondly, studies of isolated cell populations must be interpreted in combination with morphological examination of cell populations in situ. Such an approach will increase our understanding of the role of T cells in gut immunity in health and disease.

T lymphocytes in the normal human intestinal tract have been analysed in tissue sections by a double-marker immunofluorescence technique, combining antiserum to T lymphocyte antigen (HuTLA) with a monoclonal antibody detecting T cells of suppressor-cytotoxic phenotype (OKT8). The distribution of HLA-A -B, -C and Ia-like antigens in intestinal mucosa was also examined by a similar method. In small and large intestine 67 to 90% (mean 70%) of intraepithelial T lymphocytes were of suppressor-cytotoxic phenotype (OKT8+). In contrast, only 27 to 56% (mean 39%) of lamina propria T cells were OKT8+. Intestinal epithelial cells demonstrated strong membrane staining for HLA-A, -B, -C antigens. Ia-like antigens were detected on the epithelial cells of small intestinal villi, but not on colonic epithelial cells. Lamina propria macrophages expressed both HLA-A, -B, -C and Ia-like antigens, the latter having strong membrane and cytoplasmic fluorescence. The distribution of T cells with suppressor-cytotoxic or inducer phenotype in the intestinal epithelium and lamina propria may be related to the differential expression of Ia-like and HLA-A, -B, -C antigens in intestinal mucosa.

Lymphocyte subpopulations in the intestinal mucosa of patients with ulcerative colitis or Crohn's disease have been studied using a double marker immunofluorescence technique. Analysis of tissue sections revealed that the majority of intraepithelial lymphocytes (IEL) were T cells (Hle-1+ HuTLA+ UCHT1+). Of these, over 80% were of suppressor-cytotoxic phenotype (OKT8+:83 +/- 10.2%) with a small population of helper type IEL (OKT4+). Only one third of OKT8+ IEL reacted with the T cell antibody, anti-Leu-1. IEL were also Tac-, C3b-receptor- (C3RT05-), and Ig-. Within the lamina propria, OKT4+ T cells predominated (ulcerative colitis 64 +/- 6.0%; Crohn's disease 63 +/- 6.0%). Less than half of the smaller OKT8+ population in the lamina propria was Leu-1+. These finding did not differ from those seen in histologically normal tissues from controls, and are similar to those reported in the small intestine. Mononuclear cells were also isolated from the intestinal lamina propria using an enzymatic technique. The majority of lymphocytes obtained were T cells (OKT3+), with populations of OKT4+ and OKT8+ cells. Comparison of the ratio of OKT4+ to OKT8+ lymphocytes determined by immunohistological analysis with that obtained in mucosal isolates, however, suggested that the isolation procedure may deplete OKT8+ cells. These findings indicate that an imbalance of mucosal immunoregulatory T cells, as defined by monoclonal antibodies, does not occur in inflammatory bowel disease. They also emphasize that functional studies of isolated intestinal mucosal cells should be combined with morphological studies of cell populations in situ.

Lymphocyte subpopulations in human small intestinal mucosa have been studied using an immunofluorescence technique on tissue sections. In the normal intestine, the majority of intraepithelial lymphocytes (IEL) were of suppressor-cytotoxic phenotype (HuTLA+ UCHTI+ OKT8+ OKT4-; 84%). Only one-third of these OKT8+IEL reacted with anti-Leu-1, and antibody directed towards a 67,000 dalton antigen found on peripheral blood T cells. IEL failed to express the activation antigen, Tac, and also lacked detectable C3b receptor (C3RTO5-). The remaining T IEL, as well as the predominant lamina propria T lymphocytes (LPL), were OKT4+ OKT8-, helper type T cells. Most of the lamina propria OKT8+ cells were also Leu-1-. In patients with adult coeliac disease, the proportions of OKT8+ and OKT4+ lymphocytes in the epithelium were not altered. However, the proportion of OKT8+ Leu-1+TIEL was significantly increased (56 vs 32%; P less than 0.02). IEL were also HLA-DR-, Tac- and C3RTO5-. The proportion of OKT8+ cells in the lamina propria was slightly, but significantly, increased (40 vs 32%; P less than 0.005). Mucosal findings in treated patients did not differ from normal. Lymphocytes with the phenotype of natural killer cells (HNK-1) were rarely found in normal or diseased mucosa. No alterations in the proportions of circulating T lymphocytes or their subsets were found in patients with coeliac disease. These findings illustrate the heterogeneity of lymphocyte subpopulations in normal and in diseased small intestinal mucosa. The changes found in adult coeliac disease may reflect the increased traffic of IEL into the epithelium.

Spontaneous cell-mediated cytotoxicity (SCMC) has been investigated in mononuclear cells (MNC) isolated from intestinal mucosa and autologous peripheral blood from human subjects. The proportion of cells with the NK-K phenotype (Leu 7+) were substantially lower in intestinal MNC than in autologous peripheral blood. SCMC of K-562 target cells when tested at an effector to target (E:T) ratio equivalent to that used for peripheral blood MNC was markedly deficient in intestinal MNC. This was not due to the effect of EDTA and collagenase used in the isolation process. However, at high E:T, ratios, significant cytotoxicity was demonstrated for most intestines examined probably reflecting a low proportion of effector cells within the intestinal MNC population. SCMC in both intestinal and autologous peripheral blood MNC were similarly related to the Leu 7+:T ratios used in the assay indirectly suggesting that the Leu 7+ cell may be responsible for the observed cytotoxicity. It is concluded that the apparent functional difference between similar cells derived from different sites may be largely related to differing proportions of effector cells. The findings indicate the need for specific definition of the effector cell and suggest that intestinal SCMC in health and various disease states requires re-appraisal.

The proportions of T cell subsets and Leu 7+ cells and the spontaneous cell-mediated cytotoxicity (SCMC) of isolated mononuclear cells have been determined across the mesenteric vascular bed and along the intestinal mucosal-mesenteric lymph node (MLN) axis in patients undergoing abdominal surgery. Whereas the proportion of T4+ and T8+ cells were similar in simultaneously taken PVB and mesenteric venous blood (MVB), the proportion of Leu 7+ cells was higher in MVB in 16 of 17 studies (15.4 +/- 6.8%, 10.8 +/- 5.1%). Additional studies showed that the proportions of lymphocyte subsets in peripheral arterial blood are the same as those in PVB. Thus, an enrichment of Leu 7+ cells occurs across the mesenteric vascular bed. Isolated intestinal and MLN mononuclear cells contained similarly high proportions of T4+ and T8+ cells as in PVB but Leu 7+ cells made up a minority subpopulation in intestinal (1.3 +/- 0.8%) and MLN mononuclear cells (1.0 +/- 0.9%). The SCMC of intestinal and MLN mononuclear cells was low and paralleled the proportion of Leu 7+ cells. Despite the higher proportions of Leu 7+ cells in MVB, the SCMC was less than that of PVB in eight patients with inflamed intestine and not significantly different from PVB in seven patients with normal intestines. These paradoxical findings were at least in part due to inhibitory factors in mesenteric plasma. In conclusion, NK cells appear to be largely confined within the vascular system and the enrichment of Leu 7+ cells across the mesenteric vascular bed suggests that this compartmentalization may be due to differences in the traffic of lymphocyte subpopulations through the intestinal mucosa and MLN.