CD4 and arthritic joint disease: However, there is still a debate on whether Th17 cells are required for the development of K/BxN arthritis, because KRN CD4 T cells that were deficient in Rorc and unable to differentiate into Th17 cells were able to induce arthritis, while KRN CD4 T cells that were deficient in Bcl-6 and unable to differentiate into follicular helper CD4 T cells failed to induce arthritis [57,58].