Identification of immunosuppressive fractions from the rat submandibular salivary gland.

It had previously been suggested that the submandibular gland (SMG) of mice and rats may contain in vivo immunosuppressive factor(s). To identify such factor(s), we used a multi-step purification procedure of rat SMG extracts. Gel filtration chromatography of the SMG crude extract resulted in two pools of fractions with significant effects on lymphocyte reactivity in the in vitro concanavalin A (Con A) bioassay. Of these two pools, only the one with lower molecular weight resulted in the prolongation of murine skin allograft survival, the suppression of the delayed-type hypersensitivity (DTH) response to picryl chloride and the decrease in number of direct (IgM) plaque-forming cells against sheep red blood cells. Fractionation of this low molecular weight (LMW) pool through hydrophobic interaction chromatography resulted in three protein fractions designated A, B and C. Of these fractions only fraction A produced significant suppression of the DTH response. Further purification of fraction A with anion exchange chromatography produced two fractions with immunosuppressive activity in the DTH response. One fraction demonstrated on SDS-PAGE a single component of 40,000 MW, while the other had two components of 30,000 and 40,000 MW respectively.