HMOX1 and arthritic joint disease: In this study, we have investigated whether endogenous HO-1 would play a role in the effector phase of inflammatory arthritis by inducing K/BxN serum transfer arthritis in HO-1 wild type (HO-1+/+), heterozygous (HO-1+/−) and homozygous knock out (HO-1−/−) mice.