Specificity of the innate immune system: A closer look at the mosquito pattern-recognition receptor repertoire

The insect innate immune system is encoded by three major functional categories of genes that are involved in (1) recognition of invading microbes; (2) immune-signal amplification and transduction; and (3) effector mechanisms that mediate the killing and clearance of infectious microorganisms. Despite its lack of adaptive immune mechanisms and antibodymediated defences similar to those found in vertebrates, the innate immune system in insects is quite specific in its antimicrobial action. Once invading microbes are recognized through specific interaction between patternrecognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs), a variety of defence reactions can be activated. This chapter discusses the specificity of the innate immune responses at the level of PRRs, with a major focus on the mosquito Anopheles gambiae as a model system. It first provides a general overview of the insects' PRR repertoire and highlights some of its most interesting features with regard to antimicrobial defence. It then provides detailed molecular and functional descriptions of some of the best characterized PRR families.