The Co-Stimulatory Effects of MyD88-Dependent Toll-Like Receptor Signaling on Activation of Murine γδ T Cells

γδ T cells express several different toll-like receptor (TLR)s. The role of MyD88- dependent TLR signaling in TCR activation of murine γδ T cells is incompletely defined. Here, we report that Pam3CSK4 (PAM, TLR2 agonist) and CL097 (TLR7 agonist), but not lipopolysaccharide (TLR4 agonist), increased CD69 expression and Th1-type cytokine production upon anti-CD3 stimulation of γδ T cells from young adult mice (6-to 10-week-old). However, these agonists alone did not induce γδ T cell activation. Additionally, we noted that neither PAM nor CL097 synergized with anti-CD3 in inducing CD69 expression on γδ T cells of aged mice (21-to 22-month-old). Compared to young γδ T cells, PAM and CL097 increased Th-1 type cytokine production with a lower magnitude from anti-CD3- stimulated, aged γδ T cells. Vγ1(+) and Vγ4(+) cells are two subpopulations of splenic γδ T cells. PAM had similar effects in anti-CD3-activated control and Vγ4(+) subset- depleted γδ T cells; whereas CL097 induced more IFN-γ production from Vγ4(+) subset-depleted γδ T cells than from the control group. Finally, we studied the role of MyD88-dependent TLRs in γδ T cell activation during West Nile virus (WNV) infection. γδ T cell, in particular, Vγ1(+) subset expansion was significantly reduced in both MyD88- and TLR7- deficient mice. Treatment with TLR7 agonist induced more Vγ1(+) cell expansion in wild-type mice during WNV infection. In summary, these results suggest that MyD88-dependent TLRs provide co-stimulatory signals during TCR activation of γδ T cells and these have differential effects on distinct subsets.