The fixation of C3b to pneumococcal cell wall polymers as a result of activation of the alternative complement pathway.

The present study was performed in order to determine the identity of the pneumococcal cell wall polymer(s) to which C3b becomes fixed after activation of the alternative pathway. Purified pneumococcal autolysin was used to solubilize pneumococcal cell walls to which C3b had been fixed via activation of the alternative pathway. The resulting soluble cell wall polymers were then examined for the presence of C3b. Chromatographic separation of cell wall digests containing either radiolabeled teichoic acid or radiolabeled C3b demonstrated that although the elution profiles of the 2 radiolabels were similar, they were not identical. In addition, when teichoic acid-containing polymers were removed from solution by immunoabsorption with TEPC-15 myeloma, only 43 to 65% of the C3b was removed. These results demonstrate that C3b activated via the alternative pathway fixes both to teichoic acid-containing pneumococcal cell wall polymers and to other cell wall constituents and/or serum proteins bound to the cell wall.