INTERFERENCE WITH THE OXIDATIVE RESPONSE OF NEUTROPHILS BY STREPTOCOCCUS-PNEUMONIAE

Background-Pneumococcal infections are still a major clinical problem. Polymorphonuclear leucocytes (neutrophils) are considered to have a k ey role in the host's defence against Streptococcus pneumoniae but the mechanisms by which they kill the pneumococcus remain unclear. As rea ctive oxygen species are regarded as a major anti-microbial defence of phagocytes an attempt has been made to establish their role in the re sponse of neutrophils to S pneumoniae. Methods-S pneumoniae isolated f rom patients with bacteraemic pneumococcal pneumonia were incubated wi th neutrophils in suspension and superoxide production was measured by reduction of ferricytochrome c. Results-S pneumoniae did not stimulat e superoxide production alone or in the presence of normal human serum . Spontaneous superoxide production by neutrophils was actually abroga ted by S pneumoniae, as was the powerful respiratory burst stimulated by phorbol myristate acetate. This phenomenon depended on both the dos e and the viability of the bacteria. With S pneumoniae in the logarith mic phase of growth inhibitory activity was confined to the organisms themselves but with organisms undergoing autolysis it was also present in filtered supernatants, suggesting that the inhibitory activity can be attributed to a factor released during autolysis. Conclusions-S pn eumoniae can interfere with the respiratory burst of neutrophils. This property may help to explain the pathogenicity of the organism.