Pathogenesis of acute avian malaria. III. Antigen and antibody complexes as a mediator of anemia in acute Plasmodium gallinaceum infections of chickens.

In a study of antigens and antibodies found in malarious chicken blood, antigen activity was found in plasma, and in hypertonic saline eluates of blood cells. A soluble antigen was extracted from parasites liberated from erythrocytes. Two classes of antigen were differentiated, one a globulin associated "serum antigen" which was found to show identity with a serum antigen from blood of rats with acute Babesia rodhaini infection, and another that was associated with the Plasmodium gallinaceum parasite. The plasma also contained antibody to both classes of antigen. Study of blood cells from normal chickens made anemic by injections of autohemagglutinin-free malarious plasma indicated that both serum antigen and its antibody were present in eluates of the washed blood cells. Direct immunofluorescent tests of these cells with conjugated antibody to serum antigen, and with conjugated antibody to P. gallinaceum parasite antigen showed that they reacted with the antibody to serum antigen but gave no reaction with antibody to parasite antigen. From this information it is suggested that soluble complexes of serum antigen and its antibody combined with the erythrocytes, and that these complexes acted as opsonin to cause the cells to be sequestered and destroyed in the spleen, or may have fixed complement to cause intravascular hemolysis. The serologic identity of serum antigen from malarious chickens and from rats with babesiosis, and its distinction from parasite antigen, led to the speculation that it might be an autoantigenic macroglobulin.