Serologic Specificity of Immunoconglutinin Associated with Infectious Anemia of Rats and Its Role in Nonspecific Acquired Resistance

Abstract

Nonspecific resistance was induced in rats infected with filterable agent of rat infectious anemia (RIA) and in mice infected with Plasmodium chabaudi by injections of globulin of rats hyperimmunized by infections of Babesia rodhaini. The resistance was manifested by anemia that appeared earlier in passively immunized animals than it did in controls. In the mice the anemia was accompanied by reductions in parasitemia. Survival of the immunized animals was enhanced. The 19S fraction of the globulin contained immunoconglutinin (IK) activity which had a specificity for fixed C3 and was 2-mercaptoethanol sensitive. The 7S fraction contained antibody to soluble serum antigen (ABSA). Infected animals given the IK fraction had parasitemia and/or anemia and mortality that did not differ from that seen in controls. Those given the ABSA fraction had early reduction in parasitemia with anemia and enhanced survival. The protection and anemia were more pronounced in those animals given both IK and ABSA. Fluorescein-conjugated IK and ABSA reacted with blood films and spleen-impression slides of rats with acute RIA and babesiosis and of mice with acute P. chabaudi malaria. It was suggested that the reactions indicated that complexes of soluble serum antigen and ABSA had fixed complement and became bound to blood cells of the circulation and those sequestered and phagocytized in the spleen. The conglutinating action of IK may have enhanced the removal of complex-coated cells and parasites from the circulation. Further, because functionally IK is antibody to complexes of antigen, antibody and complement, it may have contributed to protection by reducing the amount of pathogenic immune complexes in the blood. In a companion paper it was reported that anemia in rats resulting from infection with rat infectious anemia (RIA) agent, Trypanosoma lewisi, Plasmodium chabaudi, and Babesia rodhaini was associated with high titers of immunoconglutinin (IK) and with cold-active hemagglutinin (CAH). After recovery, titers of IK but not CAH persisted. Rats recovered from RIA had enhanced resistance to malaria, babesiosis and trypanosomiasis, and those recovered from babesiosis and malaria were resistant to RIA. This was not a resistance to infection because experimental rats developed parasitemia from challenge as readily as did controls. It was manifested by reduced parasitemia and anemia which appeared earlier by 2 to 3 days than it did in controls and by enhanced survival. The early anemia and reduced parasitemia were accompanied by early elevaReceived for publication 24 February 1978. * This communication is Journal Article No. 8114 from the Michigan Agricultural Experiment Station. t Present address: Department of Microbiology, Faculty of Pharmacy, Chulalongkorn University, Bangkok, Thailand. * Mail reprint requests to Dr. Herbert W. Cox. ions in existing IK titers (Thoongsuwan et al., 1978). Here we present results of experiments designed to ascertain the nature of IK associated with infectious anemia of rats and its possible role in nonspecific acquired resistance. MATERIALS AND METHODS Experimental animals and infections The source of the animals used, their care and the source and maintenance of the infections were described (Thoongsuwan et al., 1978). Preparation of serum fractions Rats infected with B. rodhaini for 4-5 days were exsanguinated by cardiac puncture under ether anesthesia. Recovered serum was stored at -18 C until used. Rats that had recovered from an infection of B. rodhaini were hyperimmunized by 3 weekly intraperitoneal injections of 1 ml of whole heparinized blood from infected rats. One week after the final injection they were exsanguinated as described and recovered serum was stored at -18 C. Serum collected from blood of rats with acute infections and from hyperimmunized rats was precipitated with ammonium sulfate at 50% saturation (50% SAS). The recovered globulins were dialyzed at 4 C with repeated changes of borate buffered