Identification of Leptospiral Protein Antigens Recognized by WC1+gamma delta T Cell Subsets as Target for Development of Recombinant Vaccines

Pathogenic Leptospira species cause leptospirosis, a neglected zoonotic disease recognized as a global public health problem. It is also the cause of the most common cattle infection that results in major economic losses due to reproductive problems. gamma delta T cells play a role in the protective immune response in livestock species against Leptospira, while human gamma delta T cells also respond to Leptospira. Thus, activation of gamma delta T cells has emerged as a potential component in the optimization of vaccine strategies. Bovine gamma delta T cells proliferate and produce gamma interferon (IFN-gamma) in response to vaccination with inactivated leptospires, and this response is mediated by a specific subpopulation of the WC1-bearing gamma delta T cells. WC1 molecules are members of the group B scavenger receptor cysteine-rich (SRCR) superfamily and are composed of multiple SRCR domains, of which particular extracellular domains act as ligands for Leptospira. Since WC1 molecules function as both pattern recognition receptors and gamma delta TCR coreceptors, the WC1 system has been proposed as a novel target to engage gamma delta T cells. Here, we demonstrate the involvement of leptospiral protein antigens in the activation of WC1(+) gamma delta T cells and identify two leptospiral outer membrane proteins able to interact directly with them. Interestingly, we show that the protein-specific gamma delta T cell response is composed of WC1.1(+) and WC1.2(+) subsets, although a greater number of WC1.1(+) gamma delta T cells respond. Identification of protein antigens will enhance our understanding of the role gamma delta T cells play in the leptospiral immune response and in recombinant vaccine development.