Antibody responses to invariant antigens of Trypanosoma congolense in cattle of differing susceptibility to trypanosomiasis.

Five trypanotolerant N'Dama (Bos taurus) and five susceptible Boran (Bos indicus) cattle were challenged by tsetse flies infected with Trypanosoma congolense IL 13-E3. These animals had experienced five previous infections with T. congolense, each terminated by drug therapy. Immunoblotting and ELISA were used to determine isotype and specificity of antibody responses to trypanosome invariant antigens. Both IgM and IgG1 were elicited, but the IgG1 responses were directed against a greater diversity of antigens. A 69 kD antigen was the major invariant antigen which elicited IgM antibodies in both breeds, but the N'Damas also responded with high levels of specific IgG1. Analysis of isotypic responses to whole trypanosome extract also revealed lower levels of IgG1 and higher levels of IgM in the Borans than in the N'Damas, suggesting that a dysfunction in the switch from IgM to IgG might occur in infected Boran cattle. A 33 kD antigen appeared to elicit only IgG1. Sera from all five N'Damas and the two Borans which were most resistant to the disease reacted with this antigen prior to and following re-infection. Furthermore, during the primary T. congolense infection in the same animals, anti-33 kD antibodies were detectable in all five trypanotolerant N'Damas, but in none of the five susceptible Borans. Thus, the presence of antibodies to the 33 kD antigen of T. congolense appeared to be associated with a capacity to control the disease.