Immunosuppressive and anti-inflammatory properties of a major protein secreted from the epithelium of the rat seminal vesicles.

The nonspecies specific immunosuppressive and anti-inflammatory properties of a major protein (SV-IV) secreted from the epithelium of rat seminal vesicles (SV) are described. To detect the immunosuppressive effect, peripheral blood lymphocytes (PBL) were pretreated for 2 hr at 37 degrees with SV-IV, and the protein was maintained in the incubation medium during the whole culture time. We obtained evidence that, during preincubation of PBL and SV-IV the protein was transformed by a transglutaminase (TGase) released from PBL into modified low and high molecular weight forms able to bind to PBL surfaces. It is suggested that T lymphocytes are the possible targets of the immunosuppressive effect. SV-IV seems to inhibit only the early phase of the proliferative response of T lymphocytes to mitogens without having any direct effect on the enzymatic system involved in DNA synthesis. Moreover, the protein SV-IV was also shown to possess an anti-inflammatory property due to a block of the arachidonic acid cascade at the level of the enzyme phospholipase A2 (PLA2). The physiological significance of the immunosuppressive and anti-inflammatory properties of SV-IV are discussed in relation to different aspects of the mammalian reproduction.