Role of neutrophil antigen NA1 in an infant with autoimmune neutropenia.

A nontransfused 14-month-old female infant was investigated for persistent neutropenia of eight months' duration, with absolute neutrophil counts ranging from 410 to 935 cu mm. The patient's sera reacted with neutrophils from her own peripheral blood, from normal donors, and from her mother, all these having the neutrophil antigen NA 1, but not with neutrophils from NA 1-negative donors, including the father. The autoantibody was detectable by capillary agglutination and by indirect immunofluorescence techniques but not by complement-dependent cytotoxicity. No antibody was found in the mother's serum. Studies on three occasions showed good correlation between the appearance of circulating autoantibody and the peripheral neutrophil counts. Our observations, together with previously published reports, suggest a possible relationship of NA 1 antigen and the disease susceptibility of NA 1-positive infants to autoimmune neutropenia.