Study of pregnancy-associated alpha2-glycoprotein in relation to populations of human blood leucocytes.

Pregnancy-associated alpha2-glycoprotein (alpha2-PAG) was identified by immunofluorescence on the surface membrane of mononuclear cells from normal individuals with an extensive range of plasma concentrations of the glycoprotein. The incidence of positive cells did not correlate with plasma levels but was significantly raised in chronic lymphocytic leukaemia. Anti-alpha2-PAG antibody interfered with E and Fc rosette formation but not with production of C3 rosettes. A large proportion of C3 receptor-bearing cells (B lymphocytes) but only a tiny fraction of E-rosette-forming cells (T lymphocytes) were positive for the protein. Antibody directed against human Ia antigen markedly reduced staining for alpha2-PAG.