Suppression of human lymphocyte mitogen response by proteins of the type-D retrovirus PMFV

A type-D retrovirus, derived from a human cell line and designated PMFV, which is related to, but distinct from the Mason-Pfizer monkey virus (MPMV) suppressed the in vitro mitogen response of human lymphocytes. PMFV was suppressive either as intact virus or after disruption by ether or detergents. In kinetic studies, the time course of the interaction between suppressive virus components and lymphocytes was characterized. Neither cytotoxicity nor time shifts in optimum 3H-thymidine incorporation of responding lymphocytes were observed. The suppressive activity of the disrupted virus was diminished by heating, freeze-thawing or treatment with pronase or trypsin, indicating temperature-sensitive proteins as suppressive components. By Sephacryl S-200 gel chromatography, molecular weights of approximately 70 and 15 kDa were determined for the suppressive components which were isolated from disrupted virus or virus-producing cells but not from non-infected cells.