(A and B) ACC1-mediated arthritis in mice by passive transfer. Both arthritis score (A) and incidence (B) are shown. Four groups of B10.Q mice (6 mice in each group) were injected with PBS, ACC1, M2139, and a cocktail of M2139+ACC1, respectively. All mice received 25 μg LPS from E. coli intraperitoneally on day 5. Data represent mean ± SEM (n = 6 in each group) in A. (C and D) The cartilage binding of ACC1 to mouse cartilage was evaluated by immunohistochemical staining both in vivo (C) and in vitro (D). The knee joints and paws from adult mice were stained with H&E or toluidine blue. For in vivo staining, the knee joints from a 2-day-old neonate Cia9i mouse injected with biotinylated antibodies were used. To assess direct binding of mAbs to the tissue sections in vitro, limbs from 2-day-old naive Cia9i neonates were used. Scale bar: 100 μm (C and D). (E and F) Immunohistochemical staining of cartilage from the finger joints of two rheumatoid arthritis (RA) patients. The deparaffinized sections (5–8 μm) were treated with testicular hyaluronidase, followed by incubation with ACC1. The sections were visualized with permanent red (Dako) as color substrate. Nuclei were counterstained by hematoxylin. For positive control staining, deparaffinized sections were incubated with the mouse anti-CII mAb CIIC1 specific for triple-helical CII. Negative control staining lacked the primary anti-mouse IgG antibody. Samples were stained with ACC1, secondary antibody control (negative control), CIIC1 (positive control), and toluidine blue (TB). RAK11 and RAK15 represent two patients. Scale bar: 1,000 μm (E and F).