Interaction of clinical isolates of Streptococcus pneumoniae with human complement factor H.

PspC recruits complement factor H (FH) to the pneumococcal surface. While there is differential expression of pspC during infection, detection of PspC on the surface of viable pneumococci is difficult due to variability among PspCs. We analyzed FH binding to detect PspC expression on the surface of pneumococcal isolates from different pathological sources. Using flow cytometry, we investigated FH-binding to 89 low-passage clinical isolates classified by disease manifestation (systemic, mucosal, or carriage). Carriage isolates recruited significantly more FH to their surfaces than either systemic or mucosal isolates, and this binding was independent of capsular serotype.