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Direct microscopical detection of cells synthesizing antibody against trypanosomes by immunocytoadherence (ICA), i.e., rosette formation, was studied in 14 rabbits infected with Trypanosoma gambiense (Wellcome TS strain) and in three noninfected rabbits. Suspensions of cells from lymph nodes and spleen were incubated with fresh trypanosome suspensions (ratio 1:10, cell to trypanosomes). Suspensions of the mixtures, maintained at 4°C, were stable for several hours, and four replicate counts of each preparation gave good reproducibility (± 15%). The specificity of the reaction was demonstrated by the absence of ICA of trypanosomes to the cells of noninfected rabbits and by little or no cross-reaction with heterologous strains of trypanosomes. Evidence of the antigen-antibody nature of the reaction was obtained by blocking the ICA of the trypanosomes by prior incubation of the cells with extract of homologous trypanosome or goat antiserum to rabbit gamma globulin. The lack of passive adsorption of antibodies, in vivo and in vitro, to the lymphoid cells of normal rabbit, indicated that the rosette-forming cells were actively synthesizing antibody. The variations of the immune response (IR) index, which were calculated by taking into consideration the number of rosettes observed and the spleen weight, closely paralleled the variations in the serum agglutinin titer for the parent strain and the first relapse variant, during the first 2 weeks of infection. ICA, like the agglutination reaction, detected the type-specific antigens of the parent and relapse trypanosomes and could be a valuable tool for further studies of the immune response in African trypanosomiasis.
Supported by United States Public Health Service Training Grant G. P. 50469C.