CD4 and Arthritis: Evans-Marin et al. showed that CD4+ T cells in the lamina propria were activated before the onset of arthritis in mice with CIA, following the significant upregulation of IL-17A, tumor necrosis factor- (TNF-) α, and granulocyte-macrophage colony-stimulating factor (GM-CSF), and the severity of arthritis was significantly reduced if Th17 cells were lacking [18].