Enzyme immunoassay of specific antimalarial antibody in sera fromPlasmodium yoelii-infected mice was complicated by hypergammaglobulinemia and erythrocyte (RBC) autoantibody. Malarious serum had higher immunoglobulin levels which resulted in a substantial nonspecific adsorption of antibody to antigen uncoated microtiter wells even in the presence of a surfactant. Since it was possible that some of the antibody binding to solid phase-bound malarial antigen was also due to nonspecific adsorption, the antibody binding of nonimmune serum was compared to that of malarial immune serum diluted to an equivalent immunoglobulin concentration. This allowed differentiation of specific antimalarial antibody binding from nonspecific adsorption of immunoglobulin. Although malarial antigen was partially purified from intraerythrocytic parasites, it bound a significant amount of rabbit anti-mouse RBC antibody, indicating the presence of residual RBC antigens. Serum from immune mice, but not nonimmune mouse serum, also showed substantial binding to RBC stroma antigen, suggesting that a component of the observed antibody binding to malarial antigen was anti-RBC antibody. Hypergammaglobulinemia and the induction of RBC autoantibody may both be related to the polyclonal activating property of the malarial parasite. The presence of RBC autoantibody in serum from malaria infected mice necessitates a more conservative interpretation of specific antimalarial antibody levels until a more purified malarial antigen is available.
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