Expression of C-Reactive Protein in the Human Respiratory Tract

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Abstract
C-reactive protein (CRP) is a normal constituent of human sera synthesized by hepatocytes and induced by proinflammatory cytokines. The function of this acute-phase reactant includes activation of complement and enhancement of opsonophagocytosis. CRP binds to phosphorylcholine (ChoP), a constituent of eukaryotic membranes that is also found on the cell surface of major bacterial pathogens of the human respiratory tract, includingStreptococcus pneumoniaeandHaemophilus influenzae. The presence of CRP on mucosal surfaces and role in innate immunity in the human respiratory tract where ChoP-containing organisms reside have not been previously studied. We have shown using a monoclonal antibody to CRP that CRP is present in inflamed (0.17 to 42 μg/ml) and uninflamed (H. influenzaewas abolished when the secretions were pretreated to remove CRP. In summary, the results indicate that CRP is present in secretions of the human respiratory tract, that human respiratory epithelial cells are capable of CRP expression, and that this protein may contribute to bacterial clearance in the human respiratory tract.