tailieunhanh - Chapter 128. Pneumococcal Infections (Part 2)

Nonimmunologic Mechanisms Nonimmunologic mechanisms that protect against pneumonia include filtration of air as it passes through the nasopharynx, the glottal reflex, laryngeal closure, the cough reflex, clearance of organisms from the lower airways by ciliated cells, and ingestion by pulmonary macrophages and PMNs of small bacterial inocula that manage to reach alveolar spaces. Respiratory virus infection, chronic pulmonary disease, or heart failure compromises these mechanisms, predisposing to the development of pneumococcal pneumonia. Immunologic Mechanisms Innate Immunity Innate immune mechanisms participate in clearance of pneumococci from the nasopharynx as well as in phagocytosis by PMNs and macrophages via the microbial pattern recognition. | Chapter 128. Pneumococcal Infections Part 2 Nonimmunologic Mechanisms Nonimmunologic mechanisms that protect against pneumonia include filtration of air as it passes through the nasopharynx the glottal reflex laryngeal closure the cough reflex clearance of organisms from the lower airways by ciliated cells and ingestion by pulmonary macrophages and PMNs of small bacterial inocula that manage to reach alveolar spaces. Respiratory virus infection chronic pulmonary disease or heart failure compromises these mechanisms predisposing to the development of pneumococcal pneumonia. Immunologic Mechanisms Innate Immunity Innate immune mechanisms participate in clearance of pneumococci from the nasopharynx as well as in phagocytosis by PMNs and macrophages via the microbial pattern recognition receptor Toll-like receptor 2 TLR2 . Humoral Immunity Immunologically specific humoral mechanisms provide the best protection against pneumococcal infection. Most healthy adults have antibody to constituents of S. pneumoniae such as PspA PsaA and the cell wall however there is no convincing evidence for an opsonic role of these antibodies especially at their usual concentrations. Most healthy adults lack IgG antibody to the majority of pneumococcal capsular polysaccharides. Antibody appears after colonization infection or vaccination. In the first few weeks after colonization nonspecific mechanisms probably protect the host from infection. Thereafter newly developed anticapsular antibody provides a high degree of specific protection. Adults who are at risk of aspirating pharyngeal contents and or who have diminished mechanisms of lower airway clearance are at risk of developing pneumonia before antibody is produced. Persons with a diminished capacity to form antibody probably remain susceptible as long as they are colonized. The risk of serious pneumococcal infection is greatly increased in persons with conditions that compromise IgG synthesis and or the phagocytic function of PMNs and

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