IL6 and infection: Monocytes and macrophages produce IL-6 in response to infections or tissue injuries by stimulating pattern recognition receptors with pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) and serum IL-6 levels rise to several tens to hundreds of pg/ml, depending on the infection or injury, but in healthy condition, it is not higher than 4 pg/ml (Tanaka et al., 2012; Tanaka et al., 2014; Kang et al., 2015).