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Chapter 4 : Host Defense (Antimicrobial) Peptides and Proteins
Pathogen clearance is mediated by a complex set of strategies, ranging from the ingestion of microbes by phagocytes to the production of antimicrobial molecules, including reactive chemical species or lytic compounds. Another strategy is the production of cationic host defence proteins and peptides, compounds that play an important role in innate immunity, not only as antimicrobial agents, but also as immune regulators. Defensins members are categorized into three families based on their sizes and θ: the α-, β-, and θ-defensins. Defensins have generated a large amount of interest due to their modest in vitro antimicrobial activity against a wide range of microorganisms, including enveloped viruses, fungi, and bacteria. Host defense proteins include more than 700 structurally diverse members expressed extensively in both plants and animals. Lysozymes, also called muramidases, are small, abundant cationic enzymes that are widely distributed in plants and animals. Lactoferrin is an 80-kDa iron-binding plasma protein that belongs to the transferrin protein family, which includes serum transferrin, ovotransferrin, melanotransferrin, and the inhibitor of carbonic anhydrase. Chemokines are an extensive family of small chemotactic cytokine proteins of 7 to 10 kDa in size and include approximately 50 members in humans. Most chemokines are also cationic proteins and thus possess modest antibacterial properties in dilute medium. Host defense peptides and proteins are major components in the arsenal of our immune system.