IFNγ regulates the requirement for IL-17 in PG-induced arthritis. PG-immunized GKO/TCR-Tg mice were administered weekly i.p. injections of anti-IL-17A blocking antibody or isotype-matched control antibody (IC). Mice were also immunized with adjuvant along with anti-IL-17A blocking antibody and IC. The peripheral arthritis was assessed as a function of time. (A) Clinical arthritic scores in GKO/TCR-Tg mice treated with anti-IL-17A or IC; ** P < 0.001 comparison between anti-IL-17A and IC antibody treatments in PG-immunized mice (n = 8 mice/adjuvant groups and n = 12 mice/PG-immunized groups). (B) Representative histological images of arthritic knee joints of GKO/TCR-Tg mice treated with IC or anti-IL-17 at three weeks post immunization (F, femur; T, tibia).