FcγRIIb^wild/H1 KI mice demonstrate increased autoantibody production and are more susceptible to collagen-induced arthritis. (A) After immunization with NP-KLH, antichromatin (top) and anti-dsDNA (bottom) IgM and IgG1 titers were determined in WT and FcγRIIb^wild/H1 KI mice at days 8 and 11 and 7 d after secondary immunization. n ≥ 4. Data are representative of at least two independent experiments. (B) Antichromatin IgG titer was determined in sex- and age-matched mice between 11 and 18 mo old. n = 6 mice for the WT, and n = 8 mice for the FcγRIIb^wild/H1 KI. (C) IgG and IgM immune complex deposition in the kidney glomeruli of ageing mice was determined by immunohistofluorescence and quantified using Volocity. The relative intensity was normalized to the size of the glomeruli. The results obtained from two different ageing cohorts have been pooled. Mice were all between 14.5 and 15.5 mo old at time of sacrifice. (D) Representative incidence of arthritis after collagen injection (left). Disease severity in mice developing arthritis was scored from 1–3 per paw for a total of 1–12 per animal (right). Day 0 corresponds to the onset of disease. Data from three independent experiments were pooled. In all panels, error bars represent SEM, and p-values were determined using the Mann–Whitney two-tailed test with a risk of 5%, with the exception of D (right), in which the p-value was determined using the Kruskal–Wallis test. RU, relative units.