Figure 11.

Proposed model of locally generated C5a in the alveolar compartment. C5 derived from the vascular compartment or produced locally from various types of lung cells is cleaved by activated lung macrophages to generate biologically active C5a. The cleavage enzyme from macrophages appears to be an inducible serine protease that can be blocked by naturally occurring SLPI. After C5 cleavage, C5a causes neutrophils to migrate into the alveolar space, resulting in release of inflammatory mediators, oxidative products, and other damaging proteases. C5a may also stimulate in an autocrine manner lung macrophages to enhance the inflammatory response.