Detection and effects on platelet function of anti-platelet antibody in mule foals with experimentally induced neonatal alloimmune thrombocytopenia

Horse mares carrying mule foals were immunized during the last trimester of pregnancy with whole acid-citrate-dextrose-anticoagulated donkey blood to experimentally induce neonatal alloimmune thrombocytopenia. Thrombocytopeni a occurred in the neonatal mule foals born to immunized horse mares within 24 hours after ingestion of their dams' colostrum, Mule foals born to mares not immunized with donkey blood did not develop thrombocytopenia. These fi ndings suggest that antibodies may have been directed against a donkey plat elet antigen present in the mule foals but not present in their dams. The o bjectives of this study were to determine whether anti-platelet antibody co uld be detected in mule foals with experimentally induced neonatal alloimmu ne thrombocytopenia, to identify any platelet proteins recognized by serum antibody in these foals, and to determine if platelet function was altered by sera from these mule foals. An indirect enzyme-linked immunosorbent assa y demonstrated significantly higher absorption at 1:200 of platelet-bindabl e immunoglobulin G in serum from thrombocytopenic mule foals, compared with nonthrombocytopenic mule foals. Sera from thrombocytopenic and nonthromboc ytopenic mule reals produced similar binding patterns in western immunoblot s with donkey platelet proteins separated on sodium dodecyl sulfate polyacr ylamide gels. Maximal platelet aggregation and relative slope of aggregatio n in response to collagen were significantly inhibited after incubation wit h sera from thrombocytopenic mule foals. These results suggest that mule fo als with induced alloimmune thrombocytopenia have serum antibodies that bin d to platelets and may compete with collagen binding sites to impair platel et aggregation.