Immune depression in African trypanosomiasis: the role of antigenic competition.

The capacity of trypanosome-infected cattle to mount an immune response to a simultaneous or subsequent challenge with other trypanosomes was investigated using various clones of Trypanosoma congolense and T. brucei. In animals infected simultaneously with equal numbers of trypanosomes of two different clones, the variant-specific antibody response to one clone was severely depressed while the response to the other was not affected. In cattle infected with one clone and then subsequently challenged severely depressed depending on the time interval between the two inoculations. These observations were consistent regardless of whether the clones of trypanosomes used were derived from the same or different species. The characteristics of these responses would suggest that the inability of trypanosome-infected cattle to respond well to a simultaneous or subsequent challenge with other trypanosomes or other antigens may be due to antigenic competition.