This paper reports the results of a study of the nature of the immune response against Plasmodium berghei parasites by inbred rats. A macrophage-cytophilic antibody specific for malarial antigens was identified and characterized. Detection of the antibody on the macrophage surface was accomplished by the parasite adherence tests and by the indirect fluorescent antibody technique. Isolation and purification of the macrophage-cytophilic and opsonic antibodies from hyperimmune rat serum was accomplished by QAE-Sephadex A-50 elution chromatography, and of the macrophage-cytophilic antibody by adsorption with and elution from syngeneic macrophages as well. Characterization of the cytophilic antibody as immunoglobulin GI was done by immunoelectrophoresis and by Ouchterlony-type double diffusion in gel. Passive protection tests in weanling inbred rats have demonstrated that the opsonizing antibody conferred some protection against P. berghei. The macrophage-cytophilic antibody, on the other hand, was not protective alone but acted synergistically with the opsonizing antibody.
Studies were undertaken to determine whether rheumatoid factor (RF) was present in immune human and Aotus trivirgatus monkey sera which inhibited Plasmodium falciparum schizonts in vitro and to determine whether RF could be responsible for or contribute to merozoite agglutination in the parasite inhibition test. Additional studies were conducted to determine the effect of exogenous RF on schizont inhibition when used alone or in conjunction with immune or normal sera. RF was not detected in any of the 11 immune monkey sera or the 3 immune human sera which were tested. However, when RF was added to immune human or Aotus sera, levels of schizont inhibition increased significantly over levels obtained with immune serum alone. When RF was used alone or in conjunction with normal sera, levels of schizont inhibition were comparable to those obtained with normal serum. Furthermore, adsorption of the RF with immunoglobulin G-coated erythrocytes removed the enhancing activity. The results of this study indicate that RF, which is sometimes produced during acute or chronic malarial infection, may contribute nonspecifically to the enhanced clearance of plasmodia in vivo.
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