Abstract
CD206, a mannose receptor, is mainly expressed on the surface of alternatively activated macrophages where it acts as a pattern recognition receptor and plays a role in innate and adaptive immunity. This study investigated serum soluble CD206 (sCD206) levels in community-acquired pneumonia (CAP) and examined their clinical significance. sCD206 concentrations were measured in the sera of two independent cohorts with CAP (127 and 125 patients, respectively) and 42 controls. The expression of CD206 in the lung from autopsied cases was also examined. Patients with CAP showed significantly elevated sCD206 levels than did the controls (p < 0.0001). Notably, fatal CAP patients had more than two-fold higher sCD206 concentrations than survivors in both cohorts (p < 0.0001). Serum sCD206 concentrations were associated with Pneumonia Severity Index (PSI) and CURB-65 values. Importantly, even fatal CAP patients classified as PSI I-IV, CURB65 0-2 or age <75 years had comparatively higher levels of sCD206 than those classified as PSI V, CURB-65 3-5 or age ≥75 years. Immunohistochemically, the infiltration of CD206+ macrophages was found in the lungs of fatal cases. Elevated levels of sCD206 are associated with CAP prognosis, suggesting sCD206 might be a potential biomarker to predict severity for CAP.