Maternal alloimmunization against fetal platelet antigens: a prospective study.

Neonatal alloimmune thrombocytopenia (NAIT) is induced by maternal alloantibodies to fetal platelet antigens. This prospective study was carried out to evaluate the incidence of anti-platelet antibodies in 933 mother-child pairs where the mother and child were typed for the human platelet antigens (HPA)-1, -2, -3, -5. Sera from mismatched mother-child pairs were screened for anti-platelet antibodies, anti-HLA class I and blood group ABO IgG antibodies. Platelet-specific antibodies were anti-HPA-3a in one and anti-HPA-5b in 17 neonates, respectively. All these neonates had normal platelet counts. One woman had autoreactive antibodies. Anti-HLA class I and anti-blood group A IgG antibodies were detected in five and four neonates, respectively, born with a platelet count < 150 x 10(9)/l. None of the 11 homozygous HPA-1b mothers became immunized against their heterozygous offspring. The maternal HLA-allotypes HLA-DR52 and -DR6, typically found in individuals immunized against HPA-1a and -5b, respectively, were found in three of 11 HPA-b/b nonresponders and eight of the anti-HPA-5b responders. The results indicate that a risk for NAIT due to HPA-2 and -3 alloimmunization is low. The HLA allotypes do not predict the risk for NAIT due to HPA-1 or -5 alloimmunization. Maternal anti-HPA-5b antibodies do not correlate with the platelet count in the neonate.

Human platelet antigen gene frequencies in the Austrian population.

Gene frequencies for the human platelet antigen systems HPA-1, -2, -3, and -5 were determined directly from DNA isolated from cord blood of more than 900 randomly selected Caucasoid newborns in Vienna, Austria. Genotyping was performed by specific amplification of the respective regions coding for platelet glycoproteins GP Ib, IIb, IIIa, and Ia by PCR. These PCR products were analyzed after restriction enzyme digestion and electrophoresis. The observed gene frequencies were: HPA-1a: 0.852, HPA-1b: 0.148; HPA-2a: 0.918, HPA-2b: 0.082; HPA-3a: 0.612, HPA-3b: 0.388; HPA-5a: 0.892, HPA-5b: 0.108. There was a good fit with the Hardy-Weinberg equilibrium. Results from serological determinations and genotyping showed no discrepancies.