The ability of smooth and rough strains of Streptococcus pneumoniae to activate human complement by the alternative pathway.

Three capsulate pneumococcal strains of serotypes 1, 2 ans 3, and one non-capsulate strain of serotype 47, were found to activate human complement by the alternative pathway to a similar extent over the concentration range examined. Nevertheless, the capsulate strains, in contrast to the non-capsulate, are known to require complement attachment for phagocytosis and it is therefore postulated that the toxic by-products released cause the wave of oedema characteristic of pneumococcal lobar pneumonia.