PROBLEM: Recurrent spontaneous abortion occurs in 1 in 500 random matings and usually results in abortion of all pregnancies. If absence of antibody to a paternally derived antigen caused abortion, the woman would be expected to make antibody to the other paternal antigen and abort only half her pregnancies.
METHODS: Microvesicles were prepared from equine placentae. Acid-eluted IgG antibody was eluted from the polymorphic R80K antigen and used to type the residual R80K antigen on vesicles or on peripheral blood leucocytes.
RESULTS: In several equine sibships all the half-sibs had the same paternal R80K alloantigen. In the extended horse family descended from the stallion Nearco, three allotypes were found. The allele present was usually the grandpaternal one, but exceptions are seen. Whichever allele is transmitted all the progeny have the same alloantigen (probability of this occurring by chance = 2-45).
CONCLUSION: Because only one paternal allotype is present in all progeny, lack of antibody to the R80K antigen would result in loss of all pregnancies, not one half.