title: Alloimmunization to the PlA1 platelet antigen: results of a prospective study.
abstract: The natural history of alloimmunization to the PlA1 platelet antigen is uncertain. We followed 50 PlA1-negative pregnant women during pregnancy and for 6 months post-partum in order to determine this natural history. The cohort of PlA1-negative women was obtained by PlA1 typing 5000 women. Three PlA1-negative women formed anti-PlA1 antibodies during this prospective study, two in pregnancy and one in the immediate post-partum period. All three PlA1 antibody producers were HLA-DR3 positive, a histocompatibility phenotype that is strongly associated with alloimmunization to the PlA1 antigen. One of the three infants delivered to these mothers was thrombocytopenic (platelet count 9 x 10(9)/l). The remaining two infants had normal platelet counts at birth (160 and 174 x 10(9)/l). The HLA-A1, -B8, -DR3 and -DRw52 phenotype frequencies in the group of PlA1-negative women who did not form PlA1 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 PlA1 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 PlA1 alloantibodies will result in the delivery of a thrombocytopenic infant. These findings are relevant to programs designed to either prevent alloimmunization to the PlA1 antigen (through passive administration of anti-PlA1 immunoglobulin to at-risk PlA1-negative mothers), or to identify women at risk of delivery of thrombocytopenic infants (by antenatal screening to detect women alloimmunized to the PlA1 antigen).
authors.affiliation: Toronto Blood Transfusion Centre, Canadian Red Cross Blood Transfusion Service.
authors.forename: V S
authors.initials: VS
authors.lastname: Blanchette
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.forename: Z S
authors.initials: ZS
authors.lastname: de Friedberg
authors.forename: V A
authors.initials: VA
authors.lastname: Hogan
authors.forename: E
authors.initials: E
authors.lastname: Trudel
authors.forename: F
authors.initials: F
authors.lastname: Décary
mesh_terms: D000017:ABO Blood-Group System / Q000276:immunology; D000328:Adult; D016824:Antigens, Human Platelet; D001787:Blood Group Incompatibility / Q000276:immunology; D001792:Blood Platelets / Q000276:immunology*; D005260:Female; D015803:HLA-DR3 Antigen / Q000032:analysis; D006801:Humans; D007114:Immunization; D007231:Infant, Newborn; D039661:Integrin beta3; D007518:Isoantibodies / Q000032:analysis* / Q000096:biosynthesis; D007519:Isoantigens / Q000032:analysis / Q000276:immunology*; D049590:Postpartum Period; D011247:Pregnancy / Q000276:immunology*; D011446:Prospective Studies; D013921:Thrombocytopenia / Q000276:immunology
chemical_list: D000017:ABO Blood-Group System; D016824:Antigens, Human Platelet; D015803:HLA-DR3 Antigen; C061248:ITGB3 protein, human; D039661:Integrin beta3; D007518:Isoantibodies; D007519:Isoantigens