Granular intraepithelial lymphocytes of the rat small intestine. I. Isolation, presence in T lymphocyte-deficient rats and bone marrow origin.

Intraepithelial lymphocytes have been studied in the small intestinal epithelium of normal and thymus-deficient rats. A method is described that allows recovery of purified intraepithelial lymphocytes with high yield and viability. Granular intraepithelial lymphocytes were present in normal numbers in jejunal sections from nude rats and from adult thymectomized, irradiated, bone marrow-reconstituted rats. These probably corresponded to the cells with prominent cytoplasmic granules seen in smears of isolated intraepithelial lymphocytes. Studies in athymic chimeras indicated that both granular and nongranular intraepithelial cells differentiate from bone marrow without requirement for thymus processing and that they are relatively more radio-resistant than classical lymphocytes. It is suggested that all or most intraepithelial lymphocytes form a single cell lineage in which the degree of cytoplasmic differentiation is controlled by either the thymus or T lymphocytes. Intraepithelial lymphocytes are not postthymic T cells and their relationship to mucosal mast cells and to natural killer cells is discussed.