Cluster of differentiation 1d (CD1d) and skin aging

Abstract

CD1d is a member of CD1 family of transmembrane glycoproteins which represent a third lineage of antigen-presenting molecules. These molecules are distantly related to the classical major histocompatibility complex (MHC) molecules in the immune system [1-4]. However, unlike the first and second lineages of antigen-presenting molecules (the classical MHC class I and class II molecules) that bind peptide antigens, CD1 molecules have evolved to bind lipids and glycolipids [5-7]. CD1 family molecules are closely related to MHC class Ia and Ib proteins by sequence homology, domain organization (α1, α2, α3, and β2m), and association with β2 microglobulin rather than to class II molecules [2, 6]. In contrast to MHC class I molecule which is polymorphic, CD1 molecules are not polymorphic [1-3], and are encoded by linked genes outside the MHC complex; the gene for CD1d is located on chromosome 1 in humans [1-4]. The CD1 family is divided into two groups by sequence homology: group I which consists of CD1a,-b and-c isotypes and groupII which includes CD1d [8]. Only the group II CD1d isotypes are preserved in human, mouse, rat, rabbit, and monkey [4, 9]. Sequence similarity is substantially higher for the same isotype from different species than for different isotypes within the same species [1-3, 10], suggesting that each group of CD1 molecules could have a different function [4]. © Springer-Verlag Berlin Heidelberg 2010.