Immunoglobulin Superfamily Virus Receptors and the Evolution of Adaptive Immunity

Obligate intracellular pathogens depend on cell-surface molecules to attach and enter into host cells. Pathogen receptors may be highly specialized proteins, such as complement receptors or neurotransmitter receptors, or more ubiquitous components of cell membranes, such as integrins or sialic acid–containing oligosaccharides. The immunoglobulin superfamily (IgSF) of molecules contains several members that are expressed at the cell surface, bind diverse ligands, and contribute to a variety of cellular activities, including adhesion and immune responses. Many viruses have usurped the adhesive properties of IgSF proteins to mediate attachment (Table 1). Strategies used by viruses to engage IgSF receptors provide clues to general mechanisms by which IgSF proteins bind different types of ligands, including antigens.