tailieunhanh - Chapter 136. Meningococcal Infections (Part 5)

Host Defense Mechanisms Preventing meningococcal growth in blood requires bactericidal and opsonic antibodies, complement, and phagocytes (Fig. 136-3). The major bactericidal antibodies are IgM and IgG, which (except for serogroup B) bind to the capsular polysaccharide. Immunity to meningococci is therefore serogroup specific. Antibodies to other surface (subcapsular) antigens may confer crossserogroup protection. PorA, PorB, Opc, and LOS appear to be major targets of cross-reactivity and of serogroup B bactericidal antibodies. Infants are protected from meningococcal disease during the first months of life by passively transferred maternal IgG antibodies. As maternal antibody levels wane, the attack rate increases, peaking at. | Chapter 136. Meningococcal Infections Part 5 Host Defense Mechanisms Preventing meningococcal growth in blood requires bactericidal and opsonic antibodies complement and phagocytes Fig. 136-3 . The major bactericidal antibodies are IgM and IgG which except for serogroup B bind to the capsular polysaccharide. Immunity to meningococci is therefore serogroup specific. Antibodies to other surface subcapsular antigens may confer cross-serogroup protection. PorA PorB Opc and LOS appear to be major targets of cross-reactivity and of serogroup B bactericidal antibodies. Infants are protected from meningococcal disease during the first months of life by passively transferred maternal IgG antibodies. As maternal antibody levels wane the attack rate increases peaking at 3-9 months of age. Disease incidence declines as protective antibodies are induced by colonization with nonpathogenic bacteria that have cross-reactive antigens. In addition to N. lactamica which frequently colonizes young children some enteric bacteria have antigens that cross-react with those of meningococci. One theory relates the occurrence of some cases of meningococcal disease to the presence of high levels of IgA antibodies to meningococci since these antibodies can block the bactericidal activity of IgM. Figure 136-3 Classic pathway M8L Alternative pathway Meningococcal polysaccharide. LOS Bactericidal tyỉis Phagocytosis Bou c F uti A5. Briụnnild Ệ. Htufti BL. Lcngo t L. J ni iin JI. Loitllcc J Misnson s PrfrKtpfei Edition http CoP . iiflht Th MtSuw-HUI Csmp nHf. Inf. flit Protection from meningococcal disease involves both antimeningococcal immunoglobulins and complement. Activation of complement by antimeningococcal IgM or IgG promotes bacterial lysis via the membrane attack complex C5-C9 while C3b produced by alternative mannose-binding lectin MBL or classic pathway activation and antimeningococcal IgG2 cooperate to produce effective opsonophagocytosis. A neutrophil .

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