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xThe Regulation of Complement Activity 210Complement activity is passively regulated by protein stability and cell surface composition The C1 inhibitor, C1INH, promotes dissociation of C1 components Decay Accelerating Factors promote decay of C3 convertases 211Factor I degrades C3b and C4b Protectin inhibits the MAC attack Carboxypeptidases can inactivate the anaphylatoxins, C3a and C5a Complement Defi ciencies Microbial Complement Evasion Strategies 214Some pathogens interfere with the fi rst step of immunoglobulin-mediated complement activation 215Microbial proteins bind and inactivate complement proteins 215Microbial proteases destroy complement proteins 215Some microbes mimic or bind complement regulatory proteins The Evolutionary Origins of the Complement System 215SUMMARY 219REFERENCES 220USEFUL WEB SITES STUDY QUESTIONS Chapter 7Th e Organization and Expression of Lymphocyte Receptor Genes 225The Puzzle of Immunoglobulin Gene Structure 226Investigators proposed two early theoretical models of antibody genetics Breakthrough experiments revealed that multiple gene segments encode the light chain Multigene Organization of Ig Genes Kappa light-chain genes include V, J, and C segments 231Lambda light-chain genes pair each J segment with a particular C segment Heavy-chain gene organization includes VH, D, JJ, and CH segments Innate and infl ammatory responses can be harmful 169Innate and infl ammatory responses are regulated both positively and negatively 172Pathogens have evolved mechanisms to evade innate and infl ammatory responses 173Interactions Between the Innate and Adaptive Immune Systems 173The innate immune system activates and regulates adaptive immune responses 174Adjuvants activate innate immune responses to increase the eff ectiveness of immunizations 175Some pathogen clearance mechanisms are common to both innate and adaptive immune responses 176Ubiquity of Innate Immunity 176Plants rely on innate immune responses to combat infections 177Invertebrate and vertebrate innate immune responses show both similarities and diff erences 177SUMMARY 180REFERENCES 181USEFUL WEB SITES 182STUDY QUESTIONS 182Chapter 6Th e Complement System 187The Major Pathways of Complement Activation 189The classical pathway is initiated by antibody binding 190The lectin pathway is initiated when soluble proteins recognize microbial antigens 195The alternative pathway is initiated in three distinct ways 196The three complement pathways converge at the formation of the C5 convertase 200C5 initiates the generation of the MAC 200The Diverse Functions of Complement 201Complement receptors connect complementtagged pathogens to eff ector cells 201Complement enhances host defense against infection 204Complement mediates the interface between innate and adaptive immunities 207Complement aids in the contraction phase of the immune response 207Complement mediates CNS synapse elimination 210