Murine intestinal intraepithelial lymphocytes I. Relationship of a novel Thy-1-,Lyt-1-,Lyt-2+, granulated subpopulation to natural killer cells and mast cells.

Highly purified populations of intraepithelial lymphocytes (IEL) were obtained from the murine small intestine. We found that 84% of IEL expressed Lyt-2 and that 45-55% possessed the unique phenotype, Thy-1-,Lyt-1-,Lyt-2+. Sixty percent of IEL had granules in their cytoplasm and thus resembled the large granulated lymphocytes associated with natural killer (NK) activity. However, less than 15% of IEL had NK activity in a 6-h assay. This activity resided in a subpopulation of Lyt-2- lymphocytes, leaving a large population of Thy-1-,Lyt-1-,Lyt-2+ granulated cells (45-55% of IEL) with unknown function. Sensitive radioenzymic assays for histamine showed that IEL from healthy CBA mice do not contain this amine. IgE-binding assays revealed that IEL, unlike mast cells, do not carry high-affinity receptors for IgE. Thus, only a small percentage of granulated IEL (less than 15%) possess NK activity, whereas 45-55% of IEL have granules, lack typical characteristics of mast cells, express the unique antigenic phenotype, Thy-1-,Lyt-1-,Lyt-2+ and have unknown function.