Analysis of the effector functions of different populations of mucosal lymphocytes

Lymphocytes separated from the epithelial layer of mouse small intestine, IEL, were tested for their NK cytotoxicity against Yac-1 targets. There was little NK activity in a 4 hour assay, but high activity in an 18 hour assay, and the NK activity of IEL did not parallel that in the spleen in any of the mouse strains tested. Furthermore, IEL exerted a suppressor activity on mouse spleen NK activity. Specific T-cell cytotoxicity appeared in IEL in mice immunized with an intraperitoneal injection of P-815 tumor cells. By contrast with IEL, LPL had little NK or NK suppressor activity, but higher levels of specific T-cell cytotoxicity in tumor-immunized mice than intraepithelial lymphocytes. A high proportion of IEL had granules that stained with Giemsa and Astra blue. Furthermore many IEL carried Lyt-2+ phenotype and no other T-cell surface antigen. Intraepithelial lymphocytes appeared, therefore, to have staining and phenotype characteristics of both granular NK cells and suppressor cells. It was clear that the intestinal mucosa contained populations of immune effector cells that were heterogeneous in nature and function.