The increase in CD4+ T cells producing TGF-β among spleen cells from IFN-α-treated mice at day 21 (Figure 3G) may represent such cells that, together with TGF-β-producing macrophages (Figure 7H), would give rise to the higher TGF-β levels observed in serum (Figure 5) and lymph-node cultures (Figure 6B) from IFN-α-treated mice at the day of arthritis manifestation. This evidence concerns the gene TGFB1 and arthritic joint disease.