Question

Streptococcus pyogenes produces peptidases that lower neutrophil recruitment to the site of infection. These peptidases degrade C5a, and by lowering recruitment of neutrophils to the site of infection S. pyogenes gives itself more time to divide.

S. pyogenes produces petidases that degrade C5a to lower recruitment of neutrophils. What is C5a and how does degrading C5a interfere with neutrophil recruitment to the site of infection?

Answer 1

The complement system plays an important role in innate immune activity. C5 is a complement which when activated is cleaved by protease C5-convertase releasing C5a and C5b. C5a is a chemoattractant which accumulates/attracts complements and phagocytic cells at the site of infection. C5a attracts and activates neutrophils, monocytes and mast cells, stimulates release of inflammatory mediators like cytokines, chemokines, proteolytic enzymes and complement molecules. Streptococcal C5a peptidase cleaves C5a at the Polymorphonuclear binding site inactivating C5a, thus, retarding the influx of inflammatory cells. This gives a clearence to bacteria during the first few hours after infection.