Activation of complement represents one means of natural resistance to infection from a wide variety of potential pathogens. Recently, properdin, a positive regulator of the alternative pathway of complement, has been shown to bind to surfaces and promote complement activation. Here we studied whether properdin-mediated complement activation occurs on the surface of
Chlamydia pneumoniae, an obligate intracellular Gram-negative bacterium that causes 10 to 20% of community-acquired pneumonia. We have determined for the first time that the physiological P 2 , P 3 , and P 4 forms of human properdin bind to the surface of Chlamydia pneumoniaedirectly. The binding of these physiological forms accelerates complement activation on the Chlamydia pneumoniaesurface, as measured by C3b and C9 deposition. Finally, properdin-depleted serum could not control Chlamydia pneumoniaeinfection of HEp-2 cells compared with normal human serum. However, after addition of native properdin, the properdin-depleted serum recovered the ability to control the infection. Altogether, our data suggest that properdin is a pattern recognition molecule that plays a role in resistance to Chlamydiainfection.
- Cortes, Claudio
- Ferreira, Viviana P
- Pangburn, Michael K.
- INFECTION AND IMMUNITY Journal
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