Available pneumococcal vaccines provide only limited protection for certain at-risk populations. Fifteen healthy young adults and 11 older chronic bronchitics received 23-valent pneumococcal vaccine. ELISA showed that IgG reactive with capsular polysaccharides from Streptococcus pneumoniae serotypes 3, 4, 8, 14, and 19F increased after vaccination. Bronchitics exhibited lesser responses for four of these serotypes, although differences between the groups were significant only for serotype 3. Adsorption of postvaccination sera with pneumococcal cell wall polysaccharide significantly reduced mean antibody levels in both groups and lowered the proportion of sera that demonstrated type-specific antibody responses. Reactive IgG was largely restricted to the IgG2 subclass. Pneumococcal vaccine may provide suboptimal protection of older adults because antibody responses to some capsular polysaccharides are lower in elderly bronchitics than in healthy young adults. A substantial proportion of measured antibody reflects IgG reactive with cell wall polysaccharides rather than with type-specific, capsular constituents, suggesting that antibody responses in subjects of all ages deserve reappraisal.
Because of its prominence as a cause of disease in humans, Streptococcus pneumoniae has been the subject of intensive investigation at both the clinical level and the basic scientific level during the past century. In a number of instances, these studies have resulted in important progress toward the comprehension of basic biological principles. The areas advanced by studies of the pneumococcus include an understanding of the concept of pathogenesis of infectious disease; the development of Gram's stain for identification of bacteria in specimens from patients; the elucidation of the role of the bacterial capsule in resistance to phagocytosis by cells of the host's immune system; the demonstration that molecules other than proteins are capable of eliciting the host's humoral immune responses and later, by extension, that isolated bacterial exopolysaccharides can be used safely and effectively as vaccines in humans; the documentation of the efficacy of penicillin; the collection of conclusive evidence that DNA encodes genetic information; and the investigation of putative proteinaceous virulence factors.
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