Sex-associated differences in the immune response against fetal major histocompatibility antigens: II. Association of the female IGG1 with H-2K-encoded alloantigens

Alloantibodies against the H-2^b haplotype were produced in C3HeB female and male parental mice in response to transplantation of F₁ fetal tissue (bones). In testing IgG1 and IgG2 antibodies by means of the FACS II we found striking sex-associated differences in the isotypes produced: female mice produced much more IgG1 than male mice, although they produced comparable amounts of IgG2. Using protein-A-sepharose-purified fractions of IgG1 and IgG2a, raised in the parental females we found the specificity of this extra IgG1 to be directed against the H-2K^b private determinants, in contrast to theIgG2a which was found to be specific for H-2K^b, H-2D^b and I-A^b subregion alloantigens. The relevance of the association between H-2K alloantigens and IgG1, in context of the fetal-maternal relationship is discussed.