C1q-binding activity of serum from allogeneically and syngeneically pregnant mice

C1q-binding activity of serum during allogeneic and syngeneic pregnancy in mice was measured using the direct [125I]C1q-binding assay. In both strains there was an initial tendency for levels to rise in very early pregnancy (Days 2 and 4) followed by a progressive fall in C1q binding to a level significantly lower than that found in non-pregnant animals. The changes were present in both syngeneic and allogeneic pregnancies but the later changes were more pronounced in the latter. The presence of changes associated with syngeneic pregnancy suggests that these profiles are at least in part independent of genetic differences between mother and embryo.