Veterinary Research Communications, 14 (WJO) 113-122 Copyright 8 Kluwer Academic Publishers bv - Printed in the Netherlands THE INTERACTION BETWEEN THE IMMUNE RESPONSE OF RABBITS TO HETEROLOGOUS ANTIGENS AND A PRIMARY INFESTATION WITHZ?HZPZCEPMLUSEVERTSZEVZIRTSZ B.C. NJAUl, M. NYINDO AND A. MUTAN12 International Centre of Insect Physiology and Ecology (ICIPE), PO Box 30772, Nairobi, Kenya ‘Present address: PO Box 7824, Dar-es-Salaam, Tanzania 2Department of Zoology, University of Dar-es-Salaam, Tanzania ABsrRAcr Njau, B.C., Nyindo, M. and Mutani, A., 1990. The interaction between the immune response of rabbits to heterologous antigens and a primary infestation with Rhipicephalus ever& evertsi. Veterinary Research Communications, 14 (2), 113-122 Rhpicephalus ever&i evertsi feeding on hosts inoculated with sheep red blood cells (SRBC) and bovine serum albumin (BSA) suppressed the primary antibody response to the two antigens. In addition, while the ticks paralysed most hosts in the studies, fatality associated with this toxicosis occurred only in rabbits which had received SREX, either alone or with B!L4. Only those hosts inoculated with BSA developed any resistance against the ticks, manifested by a slight reduction of engorged weights and development of anti-tick antibodies. These results suggest that R e. eve& infestation induces a degree of reduced host immune responsiveness to heterologous antigens. Keywords: antibody, heterologous antigens, immunity, rabbit, Rhzpicephalus eve& eve&, ticks INTRODUCIION In the field livestock are exposed to numerous antigenic agents such as bacteria, viruses, toxins and protozoa. Such materials may be introduced artificially into the hosts as part of disease control programmes, as when vaccinating against rinderpest or other diseases, or naturally by parasitic arthropods and hehninths. The immuno- logical aspects of the host/parasite interactions and their genetic control have been studied and reviewed (Wakelin, 1978; Willadsen, 1980, Mitchell et al., 1982; Wikel, 1984) with the aim of understanding the mechanisms of parasite survival in a potentially hostile environment. These studies were done in laboratories on naive hosts using defined antigens in order to preclude the occurrence of antigenic competition or interaction (Taussig, 1975). Such interactions may result in either an enhanced or a reduced host response to concurrent heterologous antigens from infectious or non-infectious sources. For example, the severity of infections with Typanosoma btucei and Trypanosoma congolense in hosts exposed to Cope- bacterium parvum and Bordetella pertussis is reduced (Murray and Morrison, 1979). Similarly, the severity of Babesia microti infection in mice is reduced when this parasite is superimposed on infection with Nematospiroides dubius (Mzembe et al., 1984) or Fasciola hepatica (Fagbemi et al., 1985). In contrast, concurrent infections are enhanced in hosts parasitized by the pathogenic species of African trypanosomes (Rurangirwa et al., 1980; 1983).