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 (< 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.