CD4 and arthritic joint disease: We have previously demonstrated that the T helper (Th) 17 subset of CD4+ T cells play a central role in the pathogenesis of GPI-induced arthritis; GPI-specific CD4+ T cells were skewed to Th17 at the time of onset, and blockade of interleukin (IL) 17 resulted in a significant amelioration of arthritis [2].