Background: Neutrophil antigen 5b has been described as involved in transfusion reactions and not in neonatal alloimmune neutropenia.
Case report: Anti-5b was found in the serum of a mother of a persistently neutropenic newborn, who had several bacterial infections. The neutropenia responded to treatment with recombinant human granulocyte-colony-stimulating factor. Immunoprecipitation experiments performed with this and three other 5b antisera identified a protein, migrating from 70 to 95 kDa, as carrier of 5b. The observed pattern of migration may point to heavy glycosylation of this protein.
Results: Six 5b-negative donors were identified among 54 screened white donors, for a 5b gene frequency of 0.66.
Conclusion: Alloimmunization to 5b in pregnancy is rare. In the patients with neonatal neutropenia analyzed in the last decade, this was the first case discovered.