Serum factors influencing spontaneous rosette formation by lymphocytes of pregnant women.

The effect of sera from pregnant women on the percentage of spontaneous rosette-forming peripheral lymphocytes was investigated. Pregnancy lymphocytes displayed a significantly lower capacity to bind SRBC than control male lymphocytes. However, after an exhaustive washing, it was possible to demonstrate a significant increase of spontaneous rosettes formed by pregnancy lymphocytes. It was found that the incubation of pregnancy-washed lymphocytes with pregnancy but not homologous male serum restored to depressed levels the values of rosette-forming peripheral lymphocytes. This blocking activity was significantly higher with autologous serum than homologous pregnancy serum. Control lymphocytes were unaffected both by washing and by incubation with pregnancy sera. The blocking activity was found in the same ion-exchange chromatography fraction of pregnancy serum where paternal HLA antigens could be demonstrated, and was reproduced by a soluble HLA preparation from the husband's lymphocytes.