The etiopathogenesis of the inflammatory bowel disease (IBD), Crohns’s disease (CD) and ulcerative colitis (UC), remains unknown. In recent years, however, considerable evidence that immunological mechanisms may play an important part in the tissue damage of CD and UC has been generated. Immunologic studies have been performed extensively in recent years to characterize the inflammatory cells in diseased IBD mucosa^1,2). The histological features of IBD are consistent with increased T cell activation. CD and UC are associated with an inflammatory cell infiltate into the diseased tissue with increased numbers of T cells in the mucosa^3,4). Immunotyping of T cells has failed to show any gross abnormalities in IBD. The proportions of CD4+ to CD8+ cells is similar in both diseased and normal tissue^5,6) and there are no obvious defects in function⁷⁾. But, the findings regarding intestinal lymphocyte activating in CD and UC are contradictory. Although a number of groups describe the increased expression of lymphocyte activation antigens including 4F2, transferrin receptor, IL-2 receptor, and HLA-DR^8–10), others do not see any rise in activated lymphokines⁴⁾. Flow cytometric analysis of isolated colonic lamina propria mononuclear cells demonstrated that lymphocyte activating antigens were expressed by increased percentages of intestinal B lymphocyte, CD4+ and CD8+ T lymphocytes in both UC and CD¹¹⁾. Isolated IBD intestinal lamina propria mononuclear cells have enhanced capacity to spontaneously release soluble IL-2 receptor, which is not specific to IBD but can also be found in colonic diverticulitis¹²⁾. Native or unprimed T cells have not yet encountered processed antigen that fits their antigen receptors, and these T cells express that the surface cells will, for a short period, express high levels of the activation markers. A number of studies have demonstrated that, within the normal intestinal mucosa, a prominent population of memory (CD45RO+) T cells exists, whereas the native subset (CD45RA+) is rather small^13,14). Other recent studies have demonstrated that the established CD lesion contains a significantly reduced proportion of CD45RA+ native T lymphocytes¹⁵⁾. This preferential accumulation of memory cells has been also demonstrated by findings that the increased ratio of mononuclear cells express early activation antigens such as 4F2, primarily on B cells¹⁶⁾. B cell proliferation and differentiation into plasma cells is dependent on cytokines and factors produced by activated T cells. Meanwhile, one of the interesting immunological findings to differentiate between CD and UC is that the mucosal CD25+ cells in CD are predominantly T cells, whereas those in UC are phenotypically macrophages.

Therefore, we designed to define the intestinal lymphocytes subsets and T cell receptors in isolated lamina propria lymphocytes, including the intraepithelial lymphocytes, derived from colonoscopic mucosal biopsy specimen from patients with IBD. We expect that this methodological approach is simple, easy to perform during colonoscopic examination, and not time-required. Moreover, we believe that the discrimination of the above immunnological parameters can help us to make a diagnosis in IBD and elucidate the differences in immunopathogenesis between CD and UC.

Lymphocytes are recirculated continuously between the blood and different tissuse of the body¹⁷⁾. This migration ensures that the full repertoire of clonal lymphocytes specificities is available to respond to antigens throughout the body. Cytokines play a central role in modulating and regulating the immune system¹⁸⁾. It may therefore be anticipated that they are of critical importance in maintaining or restoring mucosal immunologic homeostasis after injury. Interleukin 2 (IL-2) is a 15-kD glycoprotein produced by activated helper T lymphocytes that is responsible for activating and maintaining proliferative and cytolytic responses mediated by both T and NK (natural killer) cells¹⁹⁾. IL-2 is essential for the proliferation, differentiation and clonal expansion of T cells and, thus, plays a central role in the regulation of cellular immunity. Normal human lamina propria mononuclear cell (LPMC) are a heightened state of activation compared with circulating lymphocytes, including increased IL-2 receptor (IL-2R) expression. An even greater proportion of LPMC expressing IL-2R has been reported in active IBD than in controls²⁰⁾. Increased serum IL-2 and IL-2R levels, as well as colonic tissue IL-2R levels, have been described in IBD^21–23). According to our study, the percentage of IL-2R in the ulcerative colitis group was significantly elevated, and showed the tendency to increase in Crohn’s disease. From this study and result, therefore, we can suggest that local T cell activation is a feature of IBD. Furthermore, drugs that diminish IL-2 production improve the course of IBD^24,25). Despite significantly elevated IL-2R level in this study, the percentage of CD4 and NK cell level saw no significant change (data not shown) and, moreover, the percentage of CD3 was significantly decreased in Crohn’s disease compared with control and there was a tendency to decrease in ulcerative colitis. These results suggest that dropped CD8 level and elevated CD3/HLA-DR level participate in an unkown mechanism which means alterations the function of lymphocytes.

Although a number of groups have described the increased expression of lymphocytes activating antigens, including 4F2, TR, IL2-R, and HLA-DR^26–29), other observations have not demonstrated any rise in activated mucosal lymphocytes. The percentage of TR in our data showed significant increase in ulcerative colitis, and significant decrease in Crohn’s disease compared with ulcerative colitis. The percentage of CD19 was significantly decreased in Crohn’s disease compared with ulcerative colitis but relatively increased in ulcerative colitis compared with control and showed a tendency to decrease in Crohn’s disease compared with control, which, possibly, results from elevated IL-2R level. Taken together, these results provide evidence that alterations of B cell function and T cell lymphocytes populations occur in the intestine and some differences are likely to happen between ulcerative colitis and Crohn’s disease.

IEL contain both TCR α/β and TCR γ/δ lymphocytes, the proportions of which vary greatly with age and housing conditions (presumably a reflection of antigenic exposure). The TCR γ/δ lymphocytes, which represent the first T cells in ontogeny and display more limited diversity than TCR α/β cells^30–32), are only present in much smaller numbers in the peripheral lymphoid tissues but are relatively abundant in the epithelia of epidermis, intestine, uterus and tongue³³⁾. Several studies have demonstrated that the TCR γ/δ lymphocytes are increased during infection with various pathogens, including Mycobacterium leprae³⁴⁾, M. tuberculosis³⁵⁾, M. bovis³⁶⁾, Leishmania donovani³⁴⁾, Listeria monocytogens³⁷⁾, Plasmodium falciparum malaria³⁸⁾, HIV³⁹⁾ and influenza A virus⁴⁰⁾. Bucht A. et al.⁴¹⁾ reported that IBD patients demonstrated a decreased proportion of TCR γ/δ lymphocytes in the inflamed mucosa compared with the macroscopically normal area of the colon. On the other hand, a significantly increased percentage of T cells bearing the TCR γ/δ was found in peripheral blood of patients with Crohn’s disease compared with healthy individuals, including that the local mucosal inflammation may influence the circulating TCR γ/δ lymphocytes population. Also, Cuvelier et al.⁴²⁾ suggested that TCR α/β cells were increased amongst IEL in Crohn’s disease and TCR γ/δ lymphocytes showed no changes in IEL and LPL. In our stud, the percentage of TCR α/β shows a slight decrease in UC but a significant decrease in Crohn’s disease, compared with control and ulcerative colitis. Also the percentage of TCR γ/δ shows a significant decrease in Crohn’s disease compared with control and ulcerative colitis, but no change in ulcerative colitis. The function of TCR γ/δ, although not fully known, has been postulated as immune surveillance at epithelial surfaces and in cellular defenses against mycobacterial organisms. Our results show similar to previous reports and suggest that these decreased TCR γ/δ and functional alterations participate in pathogenesis in IBD.

We have some pitfalls in the study. The first, in that the study group in made who of few subjects, which gives rise to a bias. The second in the percentage of variances which are related to disease activity, but we negelected those because of the very small number of subjects and it was the first study in diagnosis. However, this study will contribute an understanding of the pathogenesis of inflammatory bowel disease.

In summary, our preliminary results suggest that increased expression of IL-2R, CD3/HLA-DR indicate that activated lymphocytes in inflammatory bowel disease may be able to modulate the immune response. Also, decreased TCR γ/δ and functional alterations participate in pathogenesis in IBD. However, these findings suggest that those mechanisms may be a little different between ulcerative colitis and Crohn’s disease.