Fig. 2: R69-4 protects against cartilage proteoglycan depletion and collagen fiber breakdown, without interfering with pathogenic antibody kinetics and binding.

a The injection of R69-4 did not affect the titers of pathogenic antibodies (Ig κ) in sera at 4 time points, shown as mean ± SD (Two-way ANOVA); Serum samples were diluted by 31,250 times except the ones collected on day 21 (6250 times). b Titers of pathogenic antibodies (Ig κ) in synovial fluid (SF) did not change 24 h after R69-4 injection, shown as mean ± SD (Mann–Whitney U test, two sided); SF samples were diluted by 625 times. c Fluorescent intensity of pathogenic antibodies (IgG κ) binding to cartilage tissue did not differ with or without the pre-incubation of R69-4 (IgG λ); scale bar: 100 µm. d R69-4 rescued cartilage breakdown in CAIA; Cab4: 2 mg, d0, i.v.; R69-4: 1 mg, d1, i.v.; sacrifice: d5; Left: Toluidine blue staining, R69-4 safeguarded against the depletion of cartilage proteoglycans, particularly within the superficial layer; Right: Masson’s Trichrome staining, R69-4 protected against cartilage collagen fiber breakdown (arrow); scale bars: 200 µm (left), 50 µm (right); e R69-4 elevated the transcription of Mmp-3 from immature chondrocytes in vitro upon Cab4 stimulation (One-way ANOVA), but not upon IL-1β stimulation (One-way ANOVA); Fold change calculated after transcription levels corrected to β-actin; Data shown as mean ± SD; Cab4: 100 µg/mL, R69-4: 100 µg/mL, IL-1β: 10 ng/mL. f R69-4 did not alter the transcription of Mmp-13 from immature chondrocytes in vitro upon Cab4 stimulation (One-way ANOVA), or upon IL-1β stimulation (One-way ANOVA); Data shown as mean ± SD; Cab4: 100 µg/mL, R69-4: 100 µg/mL, IL-1β: 10 ng/mL.