Potential role of autoantibody in severe neutropenia of a patient with Kawasaki Syndrome.

Neutropenia associated with Kawasaki Syndrome (KS) has been rarely reported, and the detailed mechanisms responsible for this state are not yet elucidated. The aim of this study was to clarify the mechanisms of neutropenia in KS. We examined antibodies to known neutrophil antigens (HNA1a, HNA1b, HNA null, HNA2, HNA3, HNA4 and non-HLA antigen 9a) in a KS patient with neutropenia. We also performed the granulocyte immunofluorescence test (GIFT) using patient or control neutrophils incubated with the patient's serum at serial time points over the patient's clinical course. No specific antibody to known neutrophil antigens was detected. Flow cytometric analysis showed that autoantibodies bound to immature CD13-positive myeloid cells, which resulted in myeloid lineage maturation arrest in the bone marrow. GIFT showed that neutrophil-specific autoantibodies were produced by the patient, and the amount of autoantibody inversely correlated with the patient's neutrophil counts. The presence of an autoantibody to a novel antigen on immature myeloid cells or neutrophils is the likely the cause of severe neutropenia in this patient with KS.