Failure to detect altered rosette inhibition titres in human pregnancy serum

Six anti-lymphocyte antisera and 6 anti-lymphocyte globulin preparations were tested on serum from women in the first and second trimester of pregnancy and on appropriate sera from non-pregnant controls. There were no differences and the results do not confirm the claim that the serum of pregnant women contains a factor that will prevent human lymphocytes forming spontaneous rosettes with sheep red blood cells, and that this serum factor makes its appearance early in pregnancy.