Immune responses of cattle to African trypanosomes: protective or pathogenic? uri icon

abstract

  • Trypanosomosis in domestic livestock negatively impacts food production and economic growth in many parts of the world, particularly in sub-Saharan Africa. Current methods of control are inadequate to prevent the 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 antigenic 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 identification 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 subsequent 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 trypanotolerant and trypanosusceptible breeds of cattle have distinct antibody responses. Trypanosusceptible cattle produce high titres of polyspecific IgM but fail to produce IgG to specific trypanosome antigens. In contrast, 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, isotype-dependent effector mechanisms, such as complement activation, binding to Pc receptors, activation of phagocytic cells, neutralisation of parasite components, clearance of immune complexes and autoimmune responses, are discussed in the context of their potential impact on either susceptibility or tolerance of cattle to trypanosomosis. In addition, the links between specific cytokine patterns, macrophage/monocyte activation and depressed T cell responses that occur during trypanosome infection are presented. The identification of mechanisms that mediate depressed immune responses might suggest novel disease intervention strategies. (C) 1998 Australian Society for Parasitology. Published by Elsevier Science Ltd.
  • Trypanosomosis is the most economically important disease constraint to livestock productivity in sub-Saharan Africa and has significant negative impact in other parts of the world. Livestock are an integral component of farming systems and thus contribute significantly to food and economic security in developing countries. Current methods of control for trypanosomosis are inadequate to prevent the enormous socioeconomic losses resulting from this disease. A vaccine has been viewed as the most desirable control option. However, the complexity of the parasite?s antigenic repertoire made development of a vaccine based on the variable surface glycoprotein coat unlikely. As a result, research is now focused on identifying invariant trypanosome components as potential targets for interrupting infection or infection-mediated disease. Immunosuppression appears to be a nearly universal feature of infection with African trypanosomes and thus may represent an essential element of the host-parasite relation ship, possibly by reducing the host?s ability to mount a protective immune response. Antibody, T cell and macrophage/monocyte responses of infected cattle are depressed in both trypanosusceptible and trypanotolerant breeds of cattle. This review describes the specific T cell and monocyte/macrophage functions that are altered in trypanosome-infected cattle and compares these disorders with those that have been described in the murine model of trypanosomosis. The identification of parasite factors that induce immunosuppression and the mechanisms that mediate depressed immune responses might suggest novel disease intervention strategies

publication date

  • 1998
  • 1998
  • 1998