Chronic autoimmune neutropenia due to anti-NA2 antibody.

In exploring the immunologic causes of chronic neutropenia, we identified a persistent neutrophil-specific antibody with NA2 specificity in the blood of a nontransfused two-year-old girl with severe neutropenia. No such antibody was detected in the maternal blood. The antibody was first studied and identified when the patient was 11 months old, but she had had clinical manifestations since the age of one month. After a trial of steroid therapy, a marked but temporary reduction in the antibody titer occurred, accompanied by the rise of the neutrophils to normal level. Neutropenia reoccurred, however, when the antibody titer began to rise, despite continuation of steroid therapy. This transient response allowed the patient's neutrophils to become available and identified as NA2-positive. Although the cause of this disorder remains obscure, the data presented indicate that the anti-NA2 autoantibody is responsible for the neutropenia observed.