I-Type Lectins

I-type lectins are defined as glycan-binding proteins (excluding antibodies and T-cell receptors) in which the binding domain is homologous to the large and varied immunoglobulin superfamily (IgSF) of proteins. Among I-type lectins, the Siglec family of sialic acid–recognizing lectins is the best characterized subgroup, both structurally and functionally, and is therefore the major focus of this chapter. Details of their discovery, characterization, binding properties, and biology are provided, along with discussions of their functional roles in vertebrate biology, with most currently available information being in mammals, and multiple unusual changes during human evolution.