agents for phagocytic cells. In addition, some of the products of the coagulation system are directly antimicrobial. For example, beta-lysine, a protein produced by platelets during coagulation, can cause lysis of many Gram-positive bacteria by acting as a cationic detergent. Many acute-phase proteins of inflammation are involved in the coagulation system. Increased levels of lactoferrin and transferrin inhibit bacterial growth by binding iron, an essential bacterial nutrient. Neural regulation The innate immune response to infectious and sterile injury is modulated by neural circuits that control cytokine production period. The inflammatory reflex is a prototypical neural circuit that controls cytokine production in the spleen. Action potentials transmitted via the vagus nerve to the spleen mediate the release of acetylcholine, the neurotransmitter that inhibits cytokine release by interacting with alpha7 nicotinic acetylcholine receptors (CHRNA7) expressed on cytokine-producing cells. The motor arc of the inflammatory reflex is termed the cholinergic anti-inflammatory pathway. Pathogen-specificity The parts of the innate immune system display specificity for different pathogens. Immune evasion Innate immune system cells prevent free growth of microorganisms within the body, but many pathogens have evolved mechanisms to evade it. One strategy is intracellular replication, as practised by Mycobacterium tuberculosis, or wearing a protective capsule, which prevents lysis by complement and by phagocytes, as in Salmonella. Bacteroides species are normally mutualistic bacteria, making up a substantial portion of the mammalian gastrointestinal flora. Species such as B. fragilis are opportunistic pathogens, causing infections of the peritoneal cavity. They inhibit phagocytosis by affecting the phagocytes receptors used to engulf bacteria. They may also mimic host cells so the immune system does not recognize them as foreign. Staphylococcus aureus inhibits the ability of the phagocyte to respond to chemokine signals. M. tuberculosis, Streptococcus pyogenes, and Bacillus anthracis utilize mechanisms that directly kill the phagocyte. Bacteria and fungi may form complex biofilms, protecting them from immune cells and proteins; biofilms are present in the chronic Pseudomonas aeruginosa and Burkholderia cenocepacia infections characteristic of cystic fibrosis. Viruses Type I interferons (IFN), secreted mainly by dendritic cells, play a central role in antiviral host defense and a cell's antiviral state. Viral components are recognized by different receptors: Toll-like receptors are located in the endosomal membrane and recognize double-stranded RNA (dsRNA), MDA5 and RIG-I receptors are located in the cytoplasm and recognize long dsRNA and phosphate-containing dsRNA respectively. When the cytoplasmic receptors MDA5 and RIG-I recognize a virus the conformation between the