Slamf6 acts as a negative regulator of NKT cell expansion in the presence of a strong agonist

Abstract

Abstract Signaling lymphocyte activation marker family member 6 (Slamf6) is a cell surface signaling receptor that plays an important role in NKT cell development. Upon activation with the CD1d ligand α-galactosylceramide (αGalCer), NKT cell Slamf6 expression increases dramatically (~10-fold) and it maintains this high level of expression for at least 5 days after activation. The mechanisms through which Slamf6 regulates NKT cell function are largely unknown. To investigate the effect of Slamf6 on peripheral NKT cell populations, we challenged C57BL/6 (B6) or B6.Slamf6−/− mice with the NKT-specific agonist αGalCer. Examination of liver NKT cell numbers 3 days after challenge revealed a 50-fold increase in B6 mice over vehicle-treated controls. In contrast, we observed a 270-fold increase in NKT cells in B6.Slamf6−/− mice versus controls. An analysis of spleen NKT cells yielded similar results. A comparison of in vivo BrdU uptake by NKT cells between B6 and B6.Slamf6−/− mice revealed no significant differences in proliferation. In addition, NKT cell intracellular IFN-γ, IL-4, and TNF production between B6 and B6.Slamf6−/− mice after administration of αGalCer revealed no difference in the production of these cytokines. We next evaluated the Slamf6-specific effect on NKT cell expansion using an in vitro co-culture system. Cross-linking of Slamf6 on purified B6 NKT cells resulted in diminished NKT cell expansion and increased numbers of TUNEL+ NKT cells. Taken together, these data support a model where Slamf6 acts as a negative regulator of NKT cell expansion in the presence of a strong agonist by regulating the death threshold of NKT cells. These data suggest that Slamf6 blockade could be a useful tool to manipulate the expansion of NKT cells in vivo.