CD5L contributes to the pathogenesis of methicillin-resistant Staphylococcus aureus-induced pneumonia. 
Staphylococcus aureus is a major causative microorganism in community- and healthcare-acquired pneumonia.  CD5L is an important protein in the control of immune homeostasis.  In this study, we found that patients with S. aureus pneumonia displayed increased levels of circulating CD5L. Likewise, mice with S. aureus pneumonia had elevated CD5L levels in the lungs.  Anti-CD5L antibody protected mice from lethal pneumonia induced by methicillin-resistant S. aureus.  The survival benefit obtained with antibody against CD5L was associated with an improvement of bacterial clearance and a reduction of pulmonary inflammatory cytokines and chemokines.  Conversely, co-injection of recombinant CD5L and S. aureus markedly increased the lethality of S. aureus pneumonia.  These findings suggest that CD5L contributed to the immunopathology of S. aureus pneumonia.