WC1 proteins, expressed on bovine γδ T cells, are members of the scavenger receptor cysteine-rich (SRCR) superfamily and are coded by 13 genes (WC1-1 to WC1-13). Phosphorylation of a tyrosine in the WC1 cytoplasmic domain upon co-ligation of WC1 and TCR is required for WC1 co-receptor activity. Serologically-defined WC1.1+ γδ T cells specifically respond to the spirochete Leptospira; in contrast, WC1.2+ γδ T cells respond to the rickettsiales Anaplasma. Silencing via shRNA suggests that only cells expressing the WC1.1 type gene products WC1-1, WC1-2 or WC1-3 contribute to the γδ T cell response to the spirochete Leptospira, suggesting that expression of individual WC1 receptors encodes antigen specificity through ligation of bacteria. Comparing a representative of WC1 proteins expressed by WC1.1+ Leptospira-responsive cells (i.e., WC1-3) to a representative of WC1.2+ Leptospira-nonresponsive cells (i.e., WC1-4), we found that five out of eleven WC1-3 SRCR domains and none of the eleven WC1-4 SRCR domains bound to two Leptospira species, L. borgpetersenii and L. interrogans. Mutational analysis of WC1-3 SRCR domains suggests that the active site for bacterial binding is different from that previously reported for other SRCR proteins that bind bacteria and also that it is affected by single amino acid changes. Taken together, our data suggest that co-ligation of specific WC1 proteins and the γδ TCR by pathogen-associated molecular patterns (PAMPs) induces γδ T activation.
- Copyright © 2013 by The American Association of Immunologists, Inc.