Trypanosoma congolense: interactions between trypanosomes expressing different metacyclic variable antigen types in vitro and in vivo.

In Trypanosome congolense, the surface antigens expressed by cultured metacyclic forms are a limited and serodeme-specific subset of variable antigen types (VATs). Experiments were carried out in mammalian-form (MF) cultures, comprising dividing trypanosomes which express metacyclic VATs (M-VATs) maintained in vitro with a mammalian cell feeder layer, or in mice following infection with cultured metacyclic populations. Selective neutralization experiments were performed by incubating populations of trypanosomes with one or a combination of McAbs to remove their respective M-VATs. Deletion of one M-VAT from the population had no effect on expression and growth of other unrelated M-VATs. Deleted M-VATs were detected in very small proportions of the total population 2-7 days following neutralization. Subsequent incubation of neutralized cultures resulted in growth of deleted M-VATs which, in most cases, reached pre-neutralization levels. It appears, therefore, that in conditions where expression of M-VATs on dividing trypanosomes occurs, removal of individual M-VATs results in their re-expression within the population.