The bactericidal property of rabbit serum consists of two protein components derived from rabbit platelets. These are designated components 1 and 2. Total body x-ray irradiation of 700 r causes a striking reduction of platelets and of components 1 and 2. As little as 100 r of x-ray irradiation produce a decrease of component 1 without causing a decrease of the platelets.
Specific antiserum for rabbit platelets causes a rapid decrease in platelets and in components 1 and 2, when injected intravenously into rabbits. Studies in vitro reveal that normal rabbit serum loses its bactericidal property when antiplatelet serum is added. Highly bactericidal rat serum is not inhibited by anti-rabbit platelet antibody.
Intravenous injection of thorotrast into rabbits causes a precipitous decrease in platelets and of components 1 and 2 without producing any decrease in leukocytes or hematocrit.