Immunosuppressive 30-kDa protein in urine of pregnant women and patients with trophoblastic diseases

Urine samples obtained from normal pregnant women and patients with trophoblastic diseases contain 30-kDa protein that suppresses phytohemagglutinin-induced T cell proliferation. The immunosuppressive protein was measured by a newly developed radioimmunoassay. The 30-kDa protein was demonstrated in almost all urine samples examined, fluid from hydatid vesicles and chorionic extracts, but not in any serum samples except at low levels in some sera from patients with choriocarcinoma. During pregnancy, the level of urinary 30-kDa protein was higher in the first (1625.5 ± 1212.0 ng/ml, mean ± S.D.) and second (1457.4 ± 1332.4 ng/ml) trimesters than in the third trimester (460.6 ± 419.0 ng/ml). The urinary 30-kDa protein/hCG ratios in patients with choriocarcinoma (8.3 ± 10.9) were significantly higher than those in patients with hydatidiform mole (0.67 ± 1.00, P < 0.01) and in all trimesters than those of normal pregnant women (0.54 ± 0.44 in the first trimester, P < 0.05; 0.63 ± 0.46 in the second trimester, P < 0.05; 0.24 ± 0.17 in the third trimester, P < 0.01). There is no significant difference between the ratios in hydatidiform mole and normal pregnancy. These findings and the fast disappearance of the 30-kDa protein from the circulation suggest that the 30-kDa protein plays a part in proliferation of trophoblastic cells in, or their invasion into the host by locally suppressing the immune reaction of the host and that the increase in the urinary 30-kDa protein level, in cases of choriocarcinoma, may be due to the malignant transformation of trophoblastic cells resulting in their rapid invasion.