Encounters with Phagocytes Phagocytosis and Inflammation Phagocytosis of microbes is a major innate host defense that limits the growth and spread of pathogens. Phagocytes appear rapidly at sites of infection in conjunction with the initiation of inflammation. Ingestion of microbes by both tissue-fixed macrophages and migrating phagocytes probably accounts for the limited ability of most microbial agents to cause disease. A family of related molecules called collectins, soluble defense collagens, or pattern-recognition molecules are found in blood (mannose-binding lectins), in lung (surfactant proteins A and D), and most likely in other tissues as well and bind to carbohydrates on microbial. | Chapter 114. Molecular Mechanisms of Microbial Pathogenesis Part 7 Encounters with Phagocytes Phagocytosis and Inflammation Phagocytosis of microbes is a major innate host defense that limits the growth and spread of pathogens. Phagocytes appear rapidly at sites of infection in conjunction with the initiation of inflammation. Ingestion of microbes by both tissue-fixed macrophages and migrating phagocytes probably accounts for the limited ability of most microbial agents to cause disease. A family of related molecules called collectins soluble defense collagens or pattern-recognition molecules are found in blood mannose-binding lectins in lung surfactant proteins A and D and most likely in other tissues as well and bind to carbohydrates on microbial surfaces to promote phagocyte clearance. Bacterial pathogens seem to be ingested principally by polymorphonuclear neutrophils PMNs while eosinophils are frequently found at sites of infection with protozoan or multicellular parasites. Successful pathogens by definition must avoid being cleared by professional phagocytes. One of several antiphagocytic strategies employed by bacteria and by the fungal pathogen Cryptococcus neoformans is to elaborate large-molecular-weight surface polysaccharide antigens often in the form of a capsule that coats the cell surface. Most pathogenic bacteria produce such antiphagocytic capsules. On occasion proteins or polypeptides form capsule-like coatings on organisms such as Bacillus anthracis. As activation of local phagocytes in tissues is a key step in initiating inflammation and migration of additional phagocytes into infected sites much attention has been paid to microbial factors that initiate inflammation. Encounters with phagocytes are governed largely by the structure of the microbial constituents that elicit inflammation and detailed knowledge of these structures for bacterial pathogens has contributed greatly to our understanding of molecular mechanisms of microbial pathogenesis
