A
cysteine protease of Trypanosoma congolense (
congopain) elicited
IgG1 antibodies in those cattle which exhibited a degree of resistance to disease during experimental
infections (Authié et al. 1992, 1993). The aim of the present study was to investigate further the association between anti-
congopain antibodies and resistance to
trypanosomiasis, and to provide a lead into the mechanisms responsible for the differential responses to
congopain in cattle. Isotype characteristics and kinetics of the antibody response to
congopain were studied in three N'Dama (trypanoresistant) and three Boran (susceptible) cattle during primary
infection with T. congolense ILNat 3.1. In both groups an
IgM response to
congopain was elicited, thus demonstrating that
congopain is antigenic in both types of cattle. Most of the
IgM appeared to be incorporated into
immune complexes.
IgG was detected as free antibody;
IgG1 but not
IgG2 was detected. All three N'Dama, but none of the three Boran cattle, mounted a significant
IgG response to
congopain. Sera from 70 primary-infected cattle belonging to five breeds of differing susceptibility were tested for their reactivity to
congopain. High levels of
IgG to
congopain were observed in the two trypanotolerant breeds, whereas the three susceptible breeds had lower levels of these
antibodies. Crosses between N'Dama and Boran cattle, which exhibit an intermediate susceptibility, had intermediate levels of
antibodies. Thus, the results from experimental
infections confirmed our initial observations. However, under natural tsetse challenge, repeated
infections and trypanocidal treatments in Zebu cattle stimulated as high anti-
congopain antibody levels as in non-treated trypanotolerant taurine cattle.