INTESTINAL T-LYMPHOCYTES

The intestine is largely colonized by bacteria and further exposed to an immense array of ingested and shed immunogenic material. Therefore, the gut associated lymphoid tissue plays a major role in the human im mune system. It may even constitute a unique immune system of its own, since it has been demonstrated to differ anatomically, phenotypically , functionally and on a molecular basis from its systemic counterpart and other peripheral lymphoid tissue. This is ultimately reflected by the observation in (transgenic) mice that intraepithelial T cells can develop independently of the thymus. Along the same lines, a rapidly g rowing body of evidence suggests that human bone marrow precursors can home to the gut epithelium, rearrange their T cell receptor genes and further differentiate in the mucosal micro environment. This, and oth er features that characterize the 'diffuse' mucosal T cell infiltrate will be discussed.