[Host reactions against bacteria. Application to pneumococcal infections].

Pneumococcal infection remains a public health problem, because of its important incidence, as well for pneumonias (2 cases per 1,000 persons per year) as for bacteremias (0.5% among hospitalized patients). The fatality rate in the bacteremic cases is 37.3% and reaches 89% in the fulminant sepsis cases, which are observed especially in splenectomized patients: the spleen takes part in the host defences against Streptococcus pneumoniae, together with the phagocytosis, the antibody production and the complement activation, essentially through the alternative complement pathway-activated C3b. Bacterial opsonization remains the fundamental mechanism of the host defence in the early stages of the pneumococcal infection.