In a murine septic arthritis model, wild-type S. aureus (Newman strain) induced significantly higher synovial tumor necrosis factor (TNF)-α levels, severe arthritis, and increased mortality compared to isogenic spa mutants, demonstrating SpA functions as a critical virulence factor responsible for exacerbating disease severity and outcomes in septic arthritis (Palmqvist et al., 2002). The gene discussed is TNF; the disease is Arthritis.