TLR2 and bacterial infectious disease with sepsis: To understand how TLR2 and aging affect the humoral immune response in bacteremia, four groups of mice (wild type-young, wild type-old, TLR2−/−-young, and TLR2−/−-old) were used to analyze immunoglobulin levels in healthy conditions as well as 10 days after intravenous injection with S. aureus.