Biological Roles of Lectins in Innate Immunity: Molecular and Structural Basis for Diversity in Self/Non-Self Recognition

Lectins and other pattern recognition proteins are critical components of innate immune mechanisms in invertebrates and vertebrates. Unlike immunoglobulins, TCRs, and VLRs, which generate diversity in recognition by genetic recombination, lectins like most innate immune receptors are “hard-wired” in the germline. Therefore, one of the outstanding questions is how the innate immune system is able to cope with the great diversity of potential microbial infectious challenges. Although the concept of pattern recognition proposes that only a handful of microbial conserved surface molecules need to be recognized for successful innate immune defense, the highly diversified microbial communities to which all organisms are exposed to and the dynamic changes in surface expression components suggests that a substantial diversity in non-self recognition mechanisms may be required for immune protection. The detailed analysis of the structural basis of lectin ligand binding and the diversity and complexity of the lectin repertoires in taxa that lack adaptive immunity, such as invertebrates, strongly suggests that this is the case. Further, recent studies have extended these observations to ectothermic vertebrates. In this review we focus on