Once the infection is initiated, the recognition of infection is accomplished via the detection of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs) (see Toll-Like Receptors), and lead to the expression and secretion of different cytokines and chemokines, such as IL-6, IL-8, tumor necrosis factor (TNF)-α, and CCL2 as well as type I and III IFNs. Here, CCL2 is linked to infection.