Editorial response: Predicting protection against encapsulated pathogens.

Patients with selective immune defects have provided vivid evidence of the specific host factors that mediate defense against the pneumococcus. Rates of invasive pneumococcal infections may be increased among patients with deficiencies of complement components (involving either the classical or alternative pathway) [1–3], decreased phagocyte number and function (including neutropenia, asplenia, and perhaps specific Fcg receptor IIa allotypes) [3–7], impaired antibody production (e.g., hypogammaglobulinemia, IgG2 subclass deficiency, and selective unresponsiveness to polysaccharides) [8–10], or combined defects (e.g., sickle cell disease, asplenia, and HIV-1 infection) [11–13]. Of these factors, only levels of capsulespecific antibody are currently amenable to modulation by medical intervention.