Thus, in primed CD8+ T cells, CD27 signaling contributes to survival by upregulating anti-apoptotic Bcl-2 family members as well as Pim-1, a serine/threonine kinase capable of sustaining survival of rapidly proliferating cells 4. Given the broad distribution of CD27, it cancer metabolism signaling pathway is
not surprising that CD27 is also expressed by γδ T cells. Furthermore, studies with human γδ T cells showed that expression of CD27 marks stages of cellular differentiation. Naïve and central memory cells within the Vγ9Vδ2+ subset, which is predominant in the blood, express CD27 on the cell surface, whereas effector memory cells within this subset lack CD27 expression 5; however, there has been little information about the functional role of CD27 expressed by γδ T cells. In three related studies, the research team headed by Bruno Silva-Santos now has filled much of this knowledge gap 6–8. Investigating Selleckchem Saracatinib the development of γδ T cells in mice, Ribot and colleagues found that CD27 already functions as a regulator of differentiation in the thymus 6, where it induces expression of the lymphotoxin-β receptor as well as genes associated with transconditioning and IFN-γ production. Thus, γδ TCR+ thymocytes that express CD27 develop into producers of
IFN-γ, whereas those that do not express CD27 are unable to generate IFN-γ but produce IL-17 instead 6. This complements an earlier report from Chien’s group indicating Dipeptidyl peptidase that TCR engagement determines whether γδ thymocytes develop into IFN-γ or IL-17 producers 9. Presumably, signals through the TCR and CD27 somehow synergize in determining γδ T-cell differentiation. Importantly, the correlation between expression of cytokines and CD27 was found to be stable, extending to mature γδ T cells in the periphery 6, and was maintained even during infection 7. As pointed out by the authors 6, this lack of plasticity in CD27+ cells distinguishes γδ T cells from αβ T cells and B cells, encouraging the notion of CD27+/− γδ T-cell functional subsets. Continuing their studies in mouse models, Ribot and colleagues
next examined the role of CD27 in γδ T-cell responses to infections with herpes virus and malaria 7. Here, in IFN-γ-producing CD27+ peripheral γδ T cells, CD27 costimulation was seen to synergize with the γδ TCR, providing survival and proliferative signals that determined the extent of in vivo γδ T-cell expansion in response to these infections. In sharp contrast, IL-17-producing CD27− γδ T cells during malaria infection relied on TLR/MyD88-mediated innate immune signals, revealing an entirely different TCR-independent pathway of immune engagement, at least in this γδ T-cell functional subset. Finally, in this issue of European Journal of Immunology, Silva-Santos’s group 8 examines the functional role of CD27 expressed by Vγ9Vδ2+ human peripheral blood γδ T lymphocytes.