Inactivation of complement by mouse saliva: Enzymatic degradation of C2, C3, C4, C5, and C7☆

Abstract While searching for lymphocyte surface antigens in mouse saliva we have observed that this secretion prevented the complement-mediated lysis of lymphocyte in a microlymphocytotoxicity test. We show in this report that mouse saliva has a specific action on C2, C4, C3, C5, and C7 components which are inactivated very rapidly while C1, C6, C8, and C9 are not modified after 15 min of incubation. The action of mouse saliva is inhibited by PMSF, TLCK, and the Kunitz bovine trypsin inhibitor, which indicates the role of a tryptic-like enzyme. After fractionation on G-75, the main activity is recovered in a low molecular weight peak which is composed of a group of three to four proteins of 10–25,000 molecular weight. When mouse saliva is injected iv into rats, their complement hemolytic activity is completely abolished in the first 24 hr and then recovers to its normal level on the third day after injection. These preliminary results suggest that mouse saliva may become a useful tool for in vivo decomplementation experiments. This inhibition of the complement reaction is obtained with rat saliva but was never observed with any of the human saliva tested.