Activation status of γδ T cells dictates their effect on osteoclast generation and bone resorption.

γδ T cells, a small subset of T cell population (5-10%), forms a bridge between innate and adaptive immunity. Although the role of γδ T cells in infectious diseases and antitumor immunity is well investigated, their role in bone biology needs to be explored. Aminobisphosphonates are used as a standard treatment modality for bone related disorders and are potent activators of γδ T cells. In the present study, we have compared the effect of "activated" and "freshly isolated" γδ T cells on osteoclast generation and function. We have shown that "activated" (αCD3/CD28 + rhIL2 or BrHPP + rhIL2 stimulated) γδ T cells inhibit osteoclastogenesis, while "freshly isolated" γδ T cells enhance osteoclast generation and function. Upon stimulation with phosphoantigen (BrHPP), "freshly isolated" γδ T cells were also able to suppress osteoclast generation and function. Cytokine profiles of these cells revealed that, "freshly isolated" γδ T cells secrete higher amounts of IL6 (pro-osteoclastogenic), while "activated" γδ T cells secrete high IFNγ levels (anti-osteoclastogenic). Neutralization of IFNγ and IL6 reversed the "inhibitory" or "stimulatory" effect of γδ T cells on osteoclastogenesis. In conclusion, we have shown that, activation status and dynamics of IL6 and IFNγ secretion dictate pro and anti-osteoclastogenic role of γδ T cells.