Neonatal alloimmune thrombocytopenia associated with maternal anti-HLA antibody: a case report

Although neonatal alloimmune thrombocytopenia (NAIT) due to maternal sensitization to human platelet antigens is well described, the role of maternal anti-human lymphocyte antigen (HLA) antibodies in NAIT is not yet firmly established.

A 31-week-old girl born prematurely to a G2POA1 mother was noted to have thrombocytopenia which lasted 18 days without any evidence of infection.

Platelet-associated IgG, anti-platelet antibody, and platelet PL(A1) antigen typing were determined using a commercial solid-phase red cell adherent test. Antibodies to platelet glycoproteins human platelet antigen (HPA) 1 to 5 were determined using a commercial ELISA. Anti-HLA antibodies were assayed using a standard lymphocytotoxicity test. Activities and IgG subclass of anti-HLA antibodies in plasma of the mother and other postpartum mothers were measured using purified HLA antigens in an enzyme linked immunoassay.

Both mother and infant were positive for HPA-1 (PL(A1)) antigens. The mother's HLA phenotype was A3, A31, B7, B27. The level of platelet-associated IgG was not increased on maternal platelets; however, increased platelet-associated IgG was detected on the infant's platelets. Antibodies to platelet glycoproteins HPA1 to 5 were not detectable in the maternal plasma. Maternal serum was positive for anti-HLA antibodies, which reacted to 23 of 27 panel cells. The presence of HLA antibodies was confirmed by enzyme-linked immunoassay. Of note, the maternal antibodies reacted positively to the infant's platelets and anti-IgG anti-HLA antibodies were detected in the serum sample from the infant collected at birth. When the activity and IgG subclass of the maternal anti-HLA antibodies were compared with those of other mothers known to have high anti-HLA antibody activity, no differences were noted.

This report documents a patient with neonatal thrombocytopenia induced by maternal IgG anti-HLA antibody. Neither activity nor IgG subclass could explain the occurrence of NAIT. The factors that contribute to NAIT induced by maternal anti-HLA antibodies remain to be identified.