To investigate whether an expanded Treg compartment at the onset of S. aureus-induced arthritis is a prerequisite for the beneficial effects of Tregs on joint damage, or whether IL2 might also be a useful treatment option in septic arthritis, mice were inoculated with S. aureus and treatment with exogenous rhIL2 was started at day 3 after infection, when clinical signs of arthritis are evident (Fig. 7a). The gene discussed is IL2; the disease is arthritic joint disease.