PARASITE IMMUNE EVASION AND EXPLOITATION - REFLECTIONS AND PROJECTIONS

Recent developments in parasite immune evasion and exploitation are re viewed with special reference to the papers presented in this volume. Parasites, broadly defined, of animals with good immune responses have evolved many strategies that adapt them to survive and reproduce. The se strategies may be passive, or may involve active intervention with host immune regulation, and can be categorized as immune evasion, immu ne exploitation and molecular piracy. The concept of immune evasion be gan with Paul Ehrlich's demonstration of antigenic variation in Africa n trypanosomes and was reinforced by later ideas on molecular mimicry. Molecular mimicry is updated in the light of recent discoveries about degeneracy and plasticity of TCR/MHC-peptide recognition. Possible co nnections between two of its postulated consequences, evasion and auto immunity, are discussed. Another putative consequence of molecular mim icry, host antigenic polymorphism, is also updated. The concept of exp loitation of host immune responses by parasites has been reinforced by new data on its first known examples, especially the immune dependenc e of schistosome egg excretion. Newer examples include use of host cyt okines as parasite growth factors, virokines, viroreceptors and helmin th pseudocytokines. Finally, questions of host gene capture by viruses and possible horizontal gene transfer between host and parasite media ted by retroviruses are examined. The latter is compared with molecula r conservation as a source of molecular mimicry and other aspects of h ost-parasite coevolution.