Implication of antibodies against human leukocyte antigen in simultaneous presentation of fetal and neonatal alloimmune thrombocytopenia and neutropenia.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) and neonatal alloimmune neutropenia (NAN) are two rare complications of newborns caused by antibodies against paternal inherited antigens. Human platelet (HPA) and neutrophil antigens (HNA) are the common targets. Human leukocyte antigen (HLA) class I proteins are also expressed on platelets and neutrophils and anti-HLA antibodies have occasionally been implicated in these complications. We report a premature twin infant who presented with severe thrombocytopenia and neutropenia clinically compatible with FNAIT and NAN, from a mother with no identifiable HPA or HNA antibodies, but with very high levels of complement-fixing antibodies against paternal inherited HLA. These antibodies were also detected in the infant. HLA antibodies are commonly present in multiparous women who deliver healthy infants. They can, however, be cytotoxic and cause clinical complications after blood products transfusion (TRALI and becoming refractory to platelets transfusion) and after organ transplantation (allogeneic organ rejection).