INHIBITION OF HUMAN LYMPHOCYTE-TRANSFORMATION BY HUMAN ALPHAFOETOPROTEIN (HAFP) - COMPARISON OF FETAL AND HEPATOMA HAFP AND KINETIC STUDIES OF INVITRO IMMUNOSUPPRESSION

Abstract

Five pure isolates of HAFP from adults with tumors of the liver or stomach, as well as HAFP isolated from fetal liver, inhibit in vitro human lymphocyte transformation induced by phytomitogens, anti-human thymocyte serum and the mixed lymphocyte culture. Fetal HAFP produces 50% inhibition at concentrations of 1-5 .mu.g/ml. The HAFP isolated from tumor-bearing adults are 1-3 orders of magnitude less potent (50% inhibition achieved at approximately 20, 130, 500 and 2000 .mu.g/ml, respectively). To achieve maximum inhibition HAFP must be present at the time of mitogen addition; pre-exposure of lymphocytes to HAFP, followed by washing, does not result in lymphocyte suppression. The inhibiting effect of HAFP cannot be overcome by a 10-fold increase in mitogen concentration, implying that HAFP does not act by simple competition with the lymphocyte membrane for the mitogen combining site. HAFP may play an immunoregulatory role during fetal development.