Antigenic basis of diversity in the γδ T cell co-receptor WC1 family

WC1 co-receptors are transmembrane glycoproteins with 11 extracellular scavenger receptor cysteine rich (SRCR) domains. They are related to the CD163 family but are uniquely expressed by gamma delta T cells. We recently showed that at least 13 members comprise the WC1 gene family in cattle, a model animal species for studies of gamma delta T cell biology. Since WC1 co-receptors participate in directing functional responses by gamma delta T cells either through the ligands they bind or the signals they transduce, availability of reagents to identify the expression of individual WC1 molecules of this diverse family would be valuable in further elucidating mechanisms of gamma delta T cell responsiveness. Although monoclonal antibodies (mAbs) have been widely used to identify WC1 co-receptors on gamma delta T cells, the locations of the antigenic epitopes recognized are unknown. Here, we mapped the epitopes to particular SRCR domains and evaluated their distribution among WC1 molecules. To do this, cDNA representing the extracellular domains of seven different WC1 genes was expressed in mammalian cells and analyzed for reactivity with anti-WC1 mAbs using ELISA and Western blotting. The study included mAbs that are broadly reactive with WC1(+) gamma delta T cells and those that divide WC1(+) gamma delta T cells into functionally distinct subpopulations. We found that mAb CC15 is a pan-reactive anti-WC1 mAb recognizing an epitope in the closely related SRCR domains 2 and 7 and that this epitope is present in at least domain 2 or 7 of all seven WC1 molecules evaluated here. Five other anti-WC1 mAbs, typified by mAb IL-A29, were found to be broadly reactive, recognizing epitopes in the related SRCR domains 4 and 9 but each having a unique pattern of reactivity with the seven WO molecules. Finally, the subpopulation-specific anti-WC1 mAbs, including those that recognize either the archetypal WC1.1 or WC1.2 molecule, were found to react with epitopes in the most variable WC1 domain, i.e. domain 1, of a restricted number of WC1 co-receptors. (C) 2009 Elsevier Ltd. All rights reserved.