Using Foxp3-eGFP mice to accurately detect in vivo generated CD4+CD25+Foxp3+ Tregs, the infection with the S. aureus USA300 WT strain led to a significantly increased frequency (PBS: 11.2 ± 0.4%, WT: 17.6 ± 0.6%; mutant: 14.9 ± 0.6%) of Tregs in the spleen compared to PBS-treated mice. The gene discussed is CD4; the disease is infection.