IMMUNE-RESPONSES OF CATTLE TO AFRICAN TRYPANOSOMES - PROTECTIVE OR PATHOGENIC

Trypanosomosis in domestic livestock negatively impacts food productio n and economic growth in many parts of the world, particularly in sub- Saharan Africa. Current methods of control are inadequate to prevent t he enormous annual socio-economic losses resulting from this disease. Hope for a vaccine based on the variant surface glycoprotein coat was abandoned several years ago when the complexity of the parasite's anti genic repertoire was appreciated. As a result, research is now focused on identifying invariant trypanosome components as potential targets for interrupting infection or infection-mediated disease. The identifi cation of immune mechanisms involved in parasite and disease control, or conversely those responses that are associated with a poor clinical outcome, should facilitate the search for vaccine candidates and subs equent vaccine design strategies. To this end, comparative studies on the immune responses of trypanotolerant and trypanosusceptible breeds of cattle can be exploited. These studies have revealed that trypanoto lerant and trypanosusceptible breeds of cattle have distinct antibody responses. Trypanosusceptible cattle produce high titres of polyspecif ic IgM but fail to produce IgG to specific trypanosome antigens. In co ntrast, although T cell and macrophage/monocyte responses of infected cattle are depressed, significant differences have not been described between tolerant and susceptible breeds of cattle. In this review, iso type-dependent effector mechanisms, such as complement activation, bin ding to Pc receptors, activation of phagocytic cells, neutralisation o f parasite components, clearance of immune complexes and autoimmune re sponses, are discussed in the context of their potential impact on eit her susceptibility or tolerance of cattle to trypanosomosis. In additi on, the links between specific cytokine patterns, macrophage/monocyte activation and depressed T cell responses that occur during trypanosom e infection are presented. The identification of mechanisms that media te depressed immune responses might suggest novel disease intervention strategies. (C) 1998 Australian Society for Parasitology. Published b y Elsevier Science Ltd.