Characterization of WC1 co-receptors on functionally distinct subpopulations of ruminant gamma delta T cells.

WC1 molecules are implicated in augmenting cellular activation as well as inducing cell cycle arrest of gammadelta T cells. Since WC1 is a large multigene family differences in outcome could result from modulation of different WC1 molecules. To further investigate this family of molecules, peripheral blood WC1(+) gammadelta T cell subpopulations were evaluated by 2-D Western blotting and RT-PCR. We found 13 cDNA intracytoplasmic tail sequences with differences in signaling motifs among them and at least 20 biochemically distinguishable WC1 spots associated with cell membranes, with some in lipid rafts. An understanding of the diversity of 2-D spots could not be resolved by evaluating T cell clones, removing sialyated carbohydrates or blotting with anti-WC1.1 or anti-WC1.2-specific antibodies. Nevertheless, while the major gammadelta T cell subpopulations in blood (WC1.1(+)/WC1.2(-) and WC1.2(+)/WC1.1(-)) both had complex 2-D patterns, virtually all spots associated with WC1.2(+)/WC1.1(-) cells bore the WC1.2 epitope, distinguishing them from the WC1.1(+) cells.

Function of ruminant gammadelta T cells is defined by WC1.1 or WC1.2 isoform expression.

WC1 is a transmembrane glycoprotein and member of the scavenger receptor cysteine rich (SRCR) family that is uniquely expressed on gammadelta T cells. The WC1 isoforms referred to as WC1.1, WC1.2, and WC1.3 are expressed on discrete subpopulations of gammadelta T cells with WC1.1 and WC1.2 expressed on mostly nonoverlapping gammadelta T cell populations. Studies have demonstrated a potential role for WC1 in modulating the response of gammadelta T cells but have not converged into a single accepted paradigm. Recent investigations that examined changing representation among mononuclear cells with age and patterns of proliferation and cytokine production by subsets bearing one or more of the previously identified variants of the WC1 molecule are summarized here. While the decrease in percentages within blood in the first year of life was found to be precipitous for WC1.1+ gammadelta T cells it was not for WC1.2+ cells. While both populations proliferated to mitogen stimulation there was a bias towards responses by WC1.2+ cells. In leptospira antigen-stimulated cultures and autologous mixed lymphocyte reaction (AMLR) cultures WC1.1+ cells proliferated and produced interferon-gamma (IFN-gamma) while WC1.2+ cells did to a much lower extent. This suggested functional differences related to the isoform of WC1 expressed. Under Th1-polarizing conditions, the WC1.1+ cells also made IFN-gamma whereas the vast majority of cells expressing WC1.2 did not. Despite the difference in IFN-gamma production, cells bearing either WC1 isoform had similar transcription levels of the high affinity IL-12 receptor subunit (IL-12Rbeta2) as well as of the transcription factors T-bet and GATA-3 when cultured with IL-12. Both populations transcribed low levels of IL-10 mRNA under Th1-polarizing conditions and TGF-beta transcripts were ubiquitously expressed by each of these cell types. Cloning and sequencing of the cytoplasmic tails of the WC1 isoforms revealed a consensus ITAM in all three isoforms but a DENY sequence adjacent to one of the SH-2 binding sites of WC1.1 only. The results suggest that WC1+ gammadelta T cells differentiated on the basis of WC1 isoform expression play distinct roles in immune responses that may be dictated by WC1 intracellular signaling.

Gammadelta T cell function varies with the expressed WC1 coreceptor.

WC1 molecules are transmembrane glycoproteins belonging to the scavenger receptor cysteine-rich family and uniquely expressed on gammadelta T cells. Although participation of WC1+ gammadelta T cells in immune responses is well established, very little is understood regarding the significance of expressing different forms of the WC1 molecule. Two forms previously identified by mAbs, i.e., WC1.1 and WC1.2, are expressed by largely nonoverlapping subpopulations of gammadelta T cells. In this study it was shown that expression of the WC1.1 coreceptor was the main indicator of proliferation and IFN-gamma production in response to autologous and bacterial Ags as well as for IFN-gamma production without proliferation in Th1-polarizing, IL-12-containing cultures. Nevertheless, after culture in either Th1-polarizing or neutral conditions, mRNA was present for both T-bet and GATA-3 as well as for IL-12Rbeta2 in WC1.1+ and WC1.2+ subpopulations, and neither produced IL-4 under any conditions. Although the steady decrease in the proportion of WC1.1+ cells, but not WC1.2+ cells, within PBMC with animal aging suggested that the two subpopulations may have different roles in immune regulation, cells bearing either WC1.1 or WC1.2 expressed mRNA for regulatory cytokines IL-10 and TGF-beta, with TGF-beta being constitutively expressed by ex vivo cells. Overall, the results demonstrate that the form of the WC1 coreceptor expressed on gammadelta T cells divides them into functional subsets according to IFN-gamma production and proliferative capacity to specific stimuli as well as with regard to representation within PBMC. Finally, evidence is provided for minor differences in the intracytoplasmic tail sequences of WC1.1 and WC1.2 that may affect signaling.