Meeting Abstract

S5.9  Monday, Jan. 5  Plasticity Of The Immunoglobulin Domain In The Evolution of Immunity CANNON, J.P.*; LITMAN, G.W.; University of South Florida; University of South Florida jcannon@health.usf.edu

Immune receptors are omnipresent in multicellular organisms and comprise a vast array of molecular structures that serve to detect and eliminate pathogenic threats. The immunoglobulin (Ig) domain, a central structural feature of the antigen binding receptors that mediate adaptive immunity in jawed vertebrates, appears to play a particularly widespread role in metazoan immunity, as recent reports have also implicated Ig domains in the immune responses of protostomes such as flies and snails. We have focused on the utilization of the Ig domain in chordate immunity and have identified numerous multigene families of Ig domain-containing receptors that appear to serve roles distinct from the adaptive antigen binding receptors. Three families have received particular focus: variable region-containing chitin-binding proteins (VCBPs) of amphioxus, modular domain immune-type receptors (MDIRs) of cartilaginous fish and novel immune-type receptors (NITRs) of bony fish. All three families are present in highly diversified forms and exhibit a striking dichotomy of apparent universal presence but extensive sequence diversification among the particular taxonomic groups in which they are found. Crystal structures of VCBPs and NITRs demonstrate significant similarity to those of antigen binding receptors but at the same time exhibit key differences that imply acquisition of separate ligand binding functions. The tremendous plasticity of the Ig domain makes it a strong focus for studies of evolutionary events that have shaped modern integrated immune systems. Current data are consistent with a model of extremely rapid emergence and divergence of immune receptors, perhaps specific to individual species, as organisms contend with environments filled with pathogens that are continually selected for variation of their own molecular signatures.