Identification of leptospiral protein antigens recognized by WC1+ γδ T cell subsets as target for development of recombinant vaccines

Abstract

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 for optimization of vaccine strategies. Bovine {gamma}{delta} T cells proliferate and produce 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 identified 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.