Mice with severe combined immunodeficiency syndrome (SCID) exhibit an impairment in both T and B cell maturation, whereas myelopoiesis remains unaffected. We report here that spleens from SCID mice have undergone phenotypic expansion of cells bearing the NK-2 and asialo GM1 markers (70-80%) characteristic of NK cells and this expansion is accompanied by a 3-4-fold enrichment in NK cytolytic activity over their normal C.B-17 littermates. Furthermore, the NK cells from SCID mice do not rearrange or express T cell receptor alpha or beta genes, or a third T cell rearranging gene, gamma. These findings suggest that (a) T cell receptors are not necessary for NK-mediated cytolysis, and (b) either NK cells constitute an entirely distinct lineage or NK cell function is acquired in pre-T cells prior to the expression of T cell receptor genes.

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