Characterization and analysis of soluble suppressor factor from early human decidual cells

To assess the role of decidual cells (DC) in the maintenance of pregnancy, immunosuppressive activity of culture supernatants from human DC were investigated. Dispersed DC suspensions from decidual tissue of early pregnancies were prepared by an enzyme digestion method using collagenase and DNase, and were enriched over 90 per cent without contamination of macrophages and lymphocytes in the fraction, with specific gravity between 1.033 and 1.044 (fraction 2 [Fr2] ) by a Percoll discontinuous density gradient method. The culture supernatants of Fr2 cells suppressed the responses of normal peripheral blood lymphocytes to PHA, MLR, and killer T cell generation at the 50 per cent concentration. To determine the mechanism of the immunosuppressive activity of the culture supernatants, the effect of the supernatants on interleukin-2 and gamma-interferon production, as well as IL-2 receptor expression, on PBL was investigated. The supernatants from 3 x 10(6)/ml of DC cells inhibited not only IL-2 and gamma-INF production, but also IL-2 receptor expression, compared with normal controls. The supernatants also suppressed immunoglobulin (IgG and IgM) production by pokeweed mitogen-stimulated B cells. To purify the suppressor factor from culture supernatants of DC, serum free culture supernatants of 3 x 10(6)/ml of DC, which showed 32 per cent of inhibitory activity on MLR, were applied to gel filtration. Fractions between mw 67,000 and 43,000 suppressed the MLR. These results suggest that DC from decidua of early pregnancy excrete an immunosuppressive factor with a molecular weight between 43,000 and 67,000 daltons.