Arthropod-transmitted Parasites: Mechanisms of Immune Interaction

Knowledge of arthropod immune mechanisms has been based to alarge extent on studies of non-medically important arthropod-microbialinteractions. Investigations involving arthropods and theirimmune responses against helminth and protozoan parasites theytransmit to vertebrate hosts are relatively limited. Data availablestrongly suggest that effective responses against these parasitesare hemocyte mediated reactions, with blood cells involved inparasite recognition and effector mechanisms. It also is apparentthat parasites are very successful in evading immune destructionin compatible arthropodparasite associations by avoiding immunedetection and/or by actively inhibiting the immune processes.However, an understanding of immune evasion mechanisms operatingon behalf of the parasite is dependent on a more thorough understandingof parasite recognition, signal transduction, and effector mechanismsinvolved in arthropod immunity. Limited data are available onhemocyte recognition events, and nothing is known about thetransduction processes whereby cells convert extracellular signalsto intracellular messages that activate effector mechanisms.Any significant progress in these important areas of researchwill be limited until successful in vitro hemocyte culturesare developed. Convincing data are available from a varietyof arthropod-parasite systems that phenol oxidases play a majorrole in effector mechanisms of the immune response. However,critical biochemical studies are needed to clarify their substratespecificities and the uniqueness of these enzymes. It is essentialthat we identify specific substrates involved in effector mechanisms,and their potential storage forms, if we are to begin to understandimmune processes in arthropods. The sensitivity of HPLC withelectrochemical detection provides a valuable tool for theseinvestigations. The next several years should prove excitingin regard to our understanding of molecular/biochemical processesof arthropod immunity.