Pregnancy-associated beta 1-macroglobulin (beta 1-PAM): a new serum protein associated with pregnancy serum-derived immune complexes and ovarian cancer.

A new pregnancy-associated serum protein, beta 1-PAM, was identified following low pH dissociation and separation, by gel chromatography, of pregnancy serum-derived immune complexes. A sandwich-type micro-enzyme immunoassay was developed and blood from various groups of subjects examined for the presence of beta 1-PAM. In addition to pregnant women, only subjects with ovarian cancer (70%) had consistently high levels of the antigen. beta 1-PAM isolated from both pregnancy and ovarian cancer serum was shown to be antigenically identical and to share the same isoelectric point (pH 5.25) and ammonium sulphate precipitation range (1.1--1.5 M). The serum protein had a molecular weight of 1.5 x 10(6), especially when obtained from ovarian cancer patients. However, it was apparent that other molecular weight forms were present, particularly in material isolated from pregnancy serum, which were probably related to the subunit nature of beta 1-PAM and its association with immune complexes.