Impaired natural killer activity and expression of interleukin-2 receptor antigen in familial erythrophagocytic lymphohistiocytosis.

A 1-month-old boy with familial erythrophagocytic lymphohistiocytosis (FEL) had a barely detectable natural killer (NK) activity of 0% to 7% (median, 0.5%) with an effector/target ratio of 20:1. The number of Leu7+ and Leu11+ cells was within normal range. In terms of interleukin-2 (IL-2) receptor antigens, IL-2R/p55 (Tac) was marginally expressed whereas IL-2R/p75 related antigen recognized by YTA-1 monoclonal antibody (MAb),i.e., YTA-1 antigen, was moderately expressed on the patient's mononuclear cells. Since the NK activity was restored in vitro by IL-2 stimulation, insufficient in vivo IL-2 production or altered cooperation of IL-2R/p75 and IL-2R/p55 (Tac) in the IL-2 mediated immune response was suspected to be present. The induction of IL-2R/p55 (Tac) in vitro was found to be imparied after stimulation with IL-2, or YTA-1MAb. When the patient attained remission the IL-2R/p55 (Tac) induction had normalized, but low NK activity persisted. The results indicate that the IL-2/IL-2R system may play an important role in the etiology and pathogenesis of FEL.