Résumé
The present paper deals with the immune reaction between a monoclonal IgG1 antibody and Trypanosoma gambiense. The aggregation of trypanosomes, immune adherence to macrophages and protection against infection are associated with the antibody. IgG1-mediated clumping of trypanosomes is readily dissociated by the addition of complement. Dissociation of the clumped trypanosomes in the equivalence area released approximately fifty percent of previously bound surface antigens. These antigens were capable of binding again to new IgG1 antibody. Complement deposition rendered bivalent IgG1 antibody in the immune complex functionally univalent. Such an event in the presence of complement is of great advantage to the infected host in killing pathogens in vivo, as it allows more antibodies to attach to surface antigens and subsequently to initiate complement activity.