Tests for antibody- and cell-mediated hypersensitivity to trypanosome antigens in rabbits infected with Trypanosoma congolense.

Rabbits infected with Trypanosoma congolense were tested for immediate and delayed-type hypersensitivity responses to parasite antigens. Positive skin-test reactions were exclusively of the Arthus type, as shown by sequential histological analyses which revealed that more than 90% of the infiltrating cells at 24 hr postinjection were polymorphonuclear neutrophils. Skin reactions could be elicited in normal rabbits by intradermal injection of trypanosome antigen-antibody complexes. The absence of cell-mediated hypersensitivity to trypanosome antigens in infected rabbits was demonstrated by skin tests and by migration inhibitory factor and skin reactive factor tests. The role of the immediate-type skin reaction to trypanosome antigens in the pathology of infection and the possibility of its utilization for diagnosis are discussed.