11 - Insect Immune Recognition and Suppression

Abstract

This chapter explores the parasitoid–host interactions in which one insect grows up inside another insect. These are ideal experimental systems to study immunity. These interactions have produced the most sophisticated evolutionary strategies involving recognition measures by the host and its countermeasures by the parasitoid. Investigations into these systems have uncovered important issues related to fundamental problems of the mechanisms used, either by host insects to recognize the parasitoid or by parasitoids to evade and suppress the hosts' defense reactions, and provide valuable insights into the workings of innate immune recognition and response. Closer inspection of two different scenarios suggests that the two recognition mechanisms are not mutually exclusive and common to all multicellular organisms. Observations exhibited in the chapter provide a conceptual basis for immune suppression, involving the uptake of extracellular suppressor–lipophorin complexes and in the process driving destabilization of actin cytoskeleton. The parasitoid exploits a natural cellular clearance mechanism by depleting adhesive receptors from the cell surface, thereby precluding hemocyte spreading and phagocytosis. Although the observed similarities between CrV1 and lectin uptake reactions indicate similar mechanisms of actin-cytoskeleton inactivation, there are differences between immune suppressors and lectins. It is obvious that these highly evolved biological interactions challenge traditional understanding of how innate immune systems are able to identify highly specific targets with a limited number of recognition molecules.