Lack of IEX-1 aggravates collagen-induced arthritis (CIA). CIA was induced in WT and IEX-1 KO mice and the clinical scores (A) and cumulative incidence of arthritic mice (B) were assessed in the mice every other day after the booster immunization. Shown in (C–F) are representative macroscopic images of H&E stained joint sections prepared from WT (C&E) and IEX-1 KO (D&F) mice immunized with adjuvant only (C and D) or a mixture of CII and adjuvant (E and F). *, ** and ***, p<0.05, 0.01 and 0.001, respectively, in presence or absence of IEX-1 and n = 12. Arrow indicates pannus and scale bar, 100 µm.