TLR2 and susceptibility to pneumonia measurement: In a mouse model infected by Streptococcus pneumoniae (S. pneumoniae), alveolar macrophages isolated from old mice (21 months old) present a defective activation of Toll-like receptor 2 (TLR2) signaling leading to a delayed pro-inflammatory cytokines responses associated with enhanced susceptibility to pneumonia compared to young mice (4 months old).46