ABSTRACT: The activity of a 100–110-Kd immunosuppressive fraction (ISF), isolated from boar seminal plasma, was investigated in mice. In vitro, this fraction was found to inhibit a unidirectional mixed lymphocyte response and cell-mediated lymphocytotoxicity, as well as antisheep red blood cells (T-dependent) and antitrinitrophenylated lipopolysaccharide (T-independent) responses. The ISF also inhibited the macrophage phagocytosis of erythrocytes coated with IgG antibodies, but it did not suppress the natural killer activity. In vivo, ISF was found to lower both the primary responses to T-dependent and to T-independent antigens.
Trypsin or pronase digestion of ISF provided active molecules of 30 Kd or 2–5 Kd respectively, thus showing that the activity is due to a protein.
This ISF factor, capable of suppressing a wide variety of immune functions and remaining active after cleavage by proteases, could play a role in the lack of immune response against the spermatozoa present in the sow genital tract after intercourse. The use of this factor as a therapeutic agent in humans could eventually be considered after further molecular characterization.