IL15 and Immunodeficiency: In summary, the results presented suggest that this patient exhibits a clinical picture that is compatible with a novel immunodeficiency-like condition characterized by a) low frequency of CD56dim NK cells in peripheral blood that cannot properly acquire expression of, CD57 and CD158, and maintain expression of CD16 upon stimulation with IL-2 or IL-15; and b) an increase in the frequency and absolute numbers of CD56bright NK cells that do not down-regulate CD62L upon stimulation with these cytokines.