Comparative proteomic studies of plasma from children with pneumococcal pneumonia

Streptococcus pneumoniae is the primary pathogen causing community acquired pneumonia in children. Despite medical progress, the prevalence of complicated pneumococcal pneumonia became increased without apparent explanations. Two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) were used to compare the plasma protein profiles from children with different severities of pneumococcal pneumonia. Plasma samples from 14 cases, 7 with complicated and the other 7 with uncomplicated pneumonia, were analyzed. Complicated pneumonia was defined by the presence of pleural fluid parameters consistent with empyema, and/or a computed tomography compatible with necrotizing pneumonitis. The normal control group included 7 age-matched volunteers. By comparing the plasma proteins of patients with different severities, 4 proteins with significant differences were identified. The up-regulated proteins were haptoglobin and immunoglobulin kappa chain. The down-regulated were apolipoprotein A-I (Apo-AI) and transthyretin. All these proteins are known to take part in the inflammation reaction, which implicates the active innate immune responses in severe infections of S. pneumoniae. In addition, the up-regulated haptoglobin, which protects lung tissues against oxidative damage by the clearance of hemoglobin, can also act as an inflammatory inhibitor. Thus, our data seem to indicate that inflammation balance may take place in the occurrence of complicated pneumococcal pneumonia.