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Alloimmunization to the PI A1 platelet antigen: results of a prospective study

1990; Wiley; Volume: 74; Issue: 2 Linguagem: Inglês

10.1111/j.1365-2141.1990.tb02567.x

1365-2141

Victor S. Blanchette, Lily Chen, Zofia Salomon De Friedberg, Victoria A. Hogan, Élise Trudel, Francine Décary,

Immunodeficiency and Autoimmune Disorders

Summary The natural history of alloimmunization to the Pl A1 platelet antigen is uncertain. We followed 50 Pl A1 ‐negative pregnant women during pregnancy and for 6 months post‐partum in order to determine this natural history. The cohort of Pl A1 ‐negative women was obtained by Pl A1 typing 5000 women. Three Pl A1 ‐negative women formed anti‐Pl A1 antibodies during this prospective study, two in pregnancy and one in the immediate post‐partum period. All three Pl A1 antibody producers were HLA‐DR3 positive, a histocompatibility phenotype that is strongly associated with alloimmunization to the Pl A1 antigen. One of the three infants delivered to these mothers was thrombocytopenic (platelet count 9 x 10 9 /1). The remaining two infants had normal platelet counts at birth (160 and 174 x 10 9 /1). The HLA‐A1, ‐B8, ‐DR3 and ‐DRw52 phenotype frequencies in the group of Pl A1 ‐negative women who did not form Pl A1 antibodies ( n = 47) was similar to that found in their husbands, and that expected in a normal Caucasian population. From our data we estimate that alloimmunization to the Pl A1 antigen occurs in approximately one out of every 1000 pregnancies in a Caucasian population. It is important to recognize that not all pregnancies in which a mother has formed Pl A1 alloantibodies will result in the delivery of a thrombocytopenic infant. These findings are relevant to programs designed to either prevent alloimmunization to the Pl A1 antigen (through passive administration of anti‐Pl A1 immunoglobulin to at‐risk Pl A1 ‐negative mothers), or to identify women at risk of delivery of thrombocytopenic infants (by antenatal screening to detect women alloimmunized to the Pl A1 antigen).