CHI3L1 and susceptibility to pneumonia measurement: In both meningitis and pneumonia, YKL-40 is secreted by locally activated macrophages (Ostergaard et al. 2002) and neutrophils (Nordenbaek et al. 1999), and was proposed as a specific supplementary serological marker for the activation of granulocytes and macrophages in inflamed tissues (Rathcke and Vestergaard, 2006).