Isoimmune neonatal neutropenia due to anti-Fc(gamma) RIIIb antibody in a mother with an Fc(gamma) RIIIb deficiency

A rare case of neutropenia in a newborn due to anti-Fc(gamma) RIIIb antibod y is described. The newborn, born from the 5th pregnancy, had severe infect ion and no neutrophils. Full clinical and neutrophil count recovery was obs erved when the child was 5 weeks old. In maternal serum, panreactive granul ocyte alloantibodies were detected. The mother's and her two sisters' granu locytes appeared to be F-gamma RIIIb deficient as found using pheno- and ge notyping methods. All of them were healthy. The anti-Fc(gamma) RIIIb specif icity of antibodies was identified by the monoclonal antibody immunobilizat ion of neutrophil antigen assay. Such antibodies were not found in both sis ters with the Fc(gamma) RIIIb deficiency, although they were pregnant, one of them on the seventh occasion.