Interleukin-17A and Interleukin-17F: A Tale of Two Cytokines Page 1 The Th17 plasticity
demonstrated in these two reports comes from cells generated in canonical culture conditions
in vitro during which they were constantly exposed to instructive cytokine signals. In vivo, cells
likely receive additional signals both favoring and opposing Th17 differentiation, and the nature
and relative abundance of these signals, is inconstant. Thus, an important question is whether
Th17 cells generated in vivo exhibit the same instability. The evidence at present is both limited …