Immune response to minor variant antigen types (VATs) in a mixed VAT infection of the African trypanosomes.

It has been shown that soon after the onset of acute infection with Trypanosoma brucei gambiense, mice are able to detect immunologically small numbers of minor variant antigen types (VATs) within the population. However, in more longstanding infections, considerably larger populations of minor VATs are required to stimulate an effective immune response. As a result, larger populations of minor VATs evade immune detection and, following a decrease in parasitaemia, become part of the relapse population. We hypothesize that the development of immunosuppression increases the effectiveness of antigenic variation as an escape mechanism.