Pregnancy specific proteins: suppression of in vitro blastogenic response to mitogen by these proteins.

Immunosuppressive properties of human chorionic gonadotropin (HCG), pregnancy specific B1-glycoprotein (SP-1), human alpha foetoprotein (AFP), and human placental lactogen (HPL) in mitogen-stimulated lymphocyte transformation were studied. A pregnancy serum containing high serum levels of these specific proteins was prepared from a number of pregnancy sera. The inhibitory effect of pregnancy sera on lymphocyte response to mitogen was examined after sequential removal of each of the proteins from the pregnancy serum by affinity chromatography. Greatest decrease in the suppression was observed when human chorionic gonadotropin (HCG) alone or human chorionic gonadotropin in combination with all other three specific proteins was removed from the pregnancy serum. Pregnancy specific B1-glycoprotein (SP-1) also significantly decreased the inhibitory effect of pregnancy serum. But the other two specific proteins (AFP and HPL) had minimal effect on the decrease an immunosuppression by pregnancy serum. However, even after removal of all the four pregnancy specific proteins from the pregnancy serum, complete return to normal values for lymphocyte transformation by mitogen was not observed, which indicates the presence of some other suppressive factor(s) in the pregnancy serum.