Noncytotoxic antibodies to paternal antigens in maternal sera and placental eluates

Noncytotoxic antibodies were detected in sera from 6 of 7 primigravid women during the first trimester of pregnancy. Such antibodies directed to antigens expressed on paternal B lymphocytes were detectable within the first 4-5 weeks of gestation. Antibody activity toward paternal B lymphocytes was also detected in 6 of 10 placental eluates, and in 3 of 10 predelivery and 2 of 10 postdelivery maternal serum samples. When B lymphocytes from umbilical cord blood were used as target cells, antibodies were detected in 5 of 7 placental eluates, and in 3 of 7 predelivery and 2 of 7 postdelivery serum samples. These antibodies also reacted with selected members of a normal B lymphocyte panel. The concept of an immunological enhancing mechanism in normal pregnancy is supported by these data.