Th17 cells do not exhibit the exact same phenotype between mice and humans. In particular, hTh17 express CD161, the equivalent of murine NK1.1, a marker typically found on Natural Killer, and NKT Cells. It was confirmed these cells are not NK cells, as they are restricted by MHC II and not CD1. Murine Th17 (mTh17) cells, however, do not express this marker. In addition, hTh17 express RORγt and IL-23R constitutively, while these markers must be induced from mTh17s. CD194 and CD196 are also found only on hTh17 cells.

The origin of Th17 cells differs in humans. hTh17 are obtained exclusively from umbilical cord blood (UCB) and newborn thymii. Only hTh17 cells expressing CD161 could be induced (IL-1β & IL-23) to make IL-17 mRNA. Naïve CD4+ T cells isolated from adult blood could not be converted into Th17 cells.

Annunziato F, et al. 2008. Int. Immunol. 20:1361.
Lim HW, et al. 2008. J. Immunol. 180:122.