Natural cytotoxicity, responsiveness to interferon and morphology of intra-epithelial lymphocytes from the small intestine of the rat.

The expression of natural cytotoxicity in the gut-associated lymphoid tissue of the rat was investigated. Intra-epithelial lymphocytes (IEL) isolated from the small intestine had a similar frequency of cytotoxic and tumour target binding cells as the spleen. However, cytotoxic activity was low in Peyer's patches and mesenteric lymph node. Cytotoxic IEL exhibited similar target-cell specificity to splenic natural killer (NK) cells, and substantial antibody-dependent cell-mediated cytotoxicity. However, their cytotoxicity and lytic efficiency was not rapidly increased following exposure to interferon and IEL probably contain only a relatively small pool of pre-NK cells. IEL contained approximately 50% of cells with basophilic cytoplasmic granules, compared to approximately 2% of granule-containing mononuclear cells in the spleen. Direct observation using the uptake of acridine orange to detect cytoplasmic granules established that some cytotoxic IEL were granular. However, substantial cytotoxicity was also mediated by non-granular IEL and not all granular IEL which bound to target cells were cytotoxic. Counts of granulated cells in Giemsa-stained preparations of spleen cells and results from single-cell assays using unfractionated splenocytes suggest that the majority of target-binding cells and at least half of the naturally cytotoxic cells must also be non-granular.