Variegated Transcription of the WC1 Hybrid PRR/Co-Receptor Genes by Individual γδ T Cells and Correlation With Pathogen Responsiveness

Abstract

γδ T cells have broad reactivity and actively participate in protective immunity against tumors and infectious disease-causing organisms. In γδ-high species such as ruminants and other artiodactyls many γδ T cells bear the lineage-specific markers known as WC1. WC1 molecules are scavenger receptors coded for by a multigenic array and are closely related to SCART found on murine γδ T cells and CD163 found on a variety of cells. We have previously shown that WC1 molecules are hybrid pattern recognition receptors thereby binding pathogens as well as signaling co-receptors for the γδ T cell receptor. WC1+ γδ T cells can be divided into two major subpopulations differentiated by the WC1 genes they express and the pathogens to which they respond. Therefore, we hypothesize that optimal γδ T cell responses are contingent on pathogen binding to WC1 molecules, especially since we have shown that silencing WC1 results in an inability of γδ T cells from primed animals to respond to the pathogen Leptospira, a model system we have employed extensively. Despite this knowledge about the crucial role WC1 plays in γδ T cell biology, the pattern of WC1 gene expression by individual γδ T cells was not known but is critical to devise methods to engage γδ T cells for responses to specific pathogens. To address this gap, we generated 78 γδ T cell clones. qRT-PCR evaluation showed that approximately 75% of the clones had one to three WC1 genes transcribed but up to six per cell occurred. The co-transcription of WC1 genes by clones showed many combinations and some WC1 genes were transcribed by both subpopulations although there were differences in the overall pattern of WC1 genes transcription. Despite this overlap, Leptospira-responsive WC1+ memory γδ T cell clones were shown to have a significantly higher propensity to express WC1 molecules that are known to bind to the pathogen.

Gamma Delta TCR and the WC1 Co-Receptor Interactions in Response to Leptospira Using Imaging Flow Cytometry and STORM

“…WC1, like the TCR co-receptor CD4 as well as many other cell surface molecules, was found in protein islands or nano or microclusters on the cell membranes of quiescent γδ T cells and those islands then concatamerized with protein islands containing γδ TCR following activation of the cells. Individual γδ T cells may express more than one WC1 gene from the multigenic array ( 32 ); here we showed that homologous types of WC1 molecules clustered together in resting cells but then concatenated with islands containing other WC1 variants following cell activation. This occurred before the coalesced heterogeneous clusters of WC1 variants merged with the γδ TCR protein islands.…”

“…Unlike CD4 and CD8 coreceptors of αβ T cells, there are variants of WC1 molecules arising from the bovine WC1 multigenic array of 13 genes. There are multiple stable subpopulations of γδ T cells each expressing 1 to 6 different variants ( 32 ). These WC1 variants may differ in the number of extracellular SRCR domains as well as their endodomains ( 24 ).…”

“…These WC1 variants may differ in the number of extracellular SRCR domains as well as their endodomains ( 24 ). γδ T cells designated as WC1.1 + and WC1.2 + differ in the WC1 genes they express and in their responses to pathogens ( 22 , 25 , 32 ). For example, cells within the WC1.1 + γδ T cell subpopulation proliferate and produce IFN- γ in response to Leptospira , while many fewer WC1.2 + cells do ( 33 ).…”

“…In cattle, there are 13 WC1 molecules with 6 or 11 SRCR extracellular domains, each of which can potentially bind pathogens ( 14 ). We have shown that multiple serovars of L. interrogans as well as L. borgpetersenii can bind to specific recombinant WC1 SRCR domains in solution and that this binding is sensitive to specific amino acid mutation ( 14 ) and that 75-80% of Leptospira -responding WC1 + γδ T cell clones have transcripts for at least one WC1 molecule that has the potential to bind Leptospira ( 32 ). Here we showed direct binding to the WC1 proteins on γδ T cell membranes.…”

The impact of aging on CD4+ T cell responses to influenza infection

“…Thus, manipulating CD4 + T cell subset differentiation through various approaches may result in more effective viral clearance and faster recovery following infection and/or more robust vaccination responses in the elderly. Pre-clinical research is underway to determine if novel vaccination strategies, such as changing adjuvant composition, including co-stimulatory molecules or cytokines, can boost the CD4 + T cell response in aged mice to generate a stronger T H 1 population and better functional quality of the T FH population after infection (Baldwin et al 2018 ). Additional research has focused on employing other target molecules (such as focusing on influenza nucleoprotein instead of hemagglutinin) to enhance aging T cell responses and enhance heterosubtypic influenza immunity (McElhaney et al 2016 ).…”