Pregnancy induces an increase in the number of immunoglobulin-secreting cells.

The effect of pregnancy on the immune status of CBA mice has been measured in terms of Ig-secreting cells. Reversed plaque assays show that there is a considerable increase in numbers of IgG- and, to a lesser extent, IgM-secreting cells in the para-aortic lymph nodes. Similar but muted responses were observed in the spleen and among the lymphocytes of the peripheral blood. Analysis of cells sorted for intensity of staining for surface Ig in a fluorescence-activated cell sorter (FACS), shows that Ig-secreting cells are confined to a population of very weakly staining cells. The 'response' in syngeneic pregnancies (CBA x CBA) is at least as great as that seen in allogeneic pregnancies (CBA x C57). Active immunity to a xenogeneic erythrocyte antigen is potentiated by pregnancy.