Detection of circulating trypanosomal antigens by double antibody ELISA using antibodies to procyclic trypanosomes.

A double antibody sandwich ELISA technique has been developed for detection of antigens of African trypanosomes present in the sera of infected mammals. The assay uses a high titre, high affinity rabbit antiserum made to purified membranes of procyclic trypanosomes as "capture" reagent and a mixture of three biotin-labelled trypanosome-specific monoclonal antibodies as detecting reagent. The monoclonal antibodies were chosen on the basis of their specificity for surface membrane antigens of Trypanosoma brucei spp., the relative abundance and solubility of their specific antigen in aqueous solvents (including serum), and the fact that each monoclonal antibody binds to distinct epitopes on the same antigen molecule. Thus, antigen capture from serum and subsequent detection was achieved using as little as 10 ng/ml of whole trypanosome lysate, or the equivalent of 5000 trypanosomes/ml when solubilized material was added to normal serum in an artificial system. Using the optimized assay, antigen was detected in the sera of trypanosome-infected mice as early as 2 days after infection with T. b. rhodesiense. The results indicate that the assay allows detection of low concentrations of specific membrane antigens of T. brucei spp. of African trypanosomes and thus may have immunodiagnostic utility.