PspC was found to bind human complement factor H (FH) by Western blot analysis of D39 (pspC ؉ ) and an isogenic mutant TRE108 (pspC). We confirmed that PspA does not bind FH, while purified PspC binds FH very strongly. The binding of FH to exponentially growing pneumococci varied among different isolates when analyzed by fluorescence activated cell sorting analysis.

Previous studies suggested that PspC is important in adherence and colonization within the nasopharynx. In this study, we conducted mutational studies to further identify the role PspC plays in the pathogenesis of pneumococci. pspC and/or pspA was insertionally inactivated in a serotype 2 Streptococcus pneumoniae strain and in a serotype 19 S. pneumoniae strain. In the mouse colonization model, pneumococcal strains with mutations in pspC were significantly attenuated in their abilities to colonize. In a mouse pneumonia model, strains with mutations in pspC were unable to infect or multiply within the lung. Using reverse transcriptase PCR we were able to demonstrate that pspC is actively transcribed in vivo, when the bacteria are growing in the nasal cavity and in the lungs. In the bacteremia model, a strain mutated for pspC alone behaved like the wild type, but the absence of both pspC and pspA caused accelerated clearance of the bacteria. Intranasal immunization with PspC with cholera toxin subunit B as an adjuvant protected against intranasal challenge. Evidence was also obtained that revertants that spontaneously acquired PspC expression could multiply and colonize the nasal tissue. This latter finding strongly indicates that pneumococci are actively metabolizing and growing while in the nasopharynx.

PspC is one of three designations for a pneumococcal surface protein whose gene is present in approximately 75% of all Streptococcus pneumoniae strains. Under the name SpsA, the protein has been shown to bind secretory immunoglobulin A (S. Hammerschmidt, S. R. Talay, P. Brandtzaeg, and G. S. Chhatwal, Mol. Microbiol. 25:1113-1124, 1997). Under the name CbpA, the protein has been shown to interact with human epithelial and endothelial cells (C. Rosenow et al., Mol. Microbiol. 25:819-829, 1997). The gene is paralogous to the pspA gene in S. pneumoniae and was thus called pspC (A. Brooks-Walter, R. C. Tart, D. E. Briles, and S. K. Hollingshead, Abstracts of the 97th General Meeting of the American Society for Microbiology 1997). Sequence comparisons of five published and seven new alleles reveal that this gene has a mosaic structure, and modular domains have contributed to gene diversity during evolution. Two major clades exist: clade A alleles are larger and contain an extra module that is shared with many pspA alleles; clade B alleles are smaller and lack this pspA-like domain. All alleles have a proline-rich domain and a choline-binding repeat domain that show 0% divergence from similar domains in the PspA protein. Immunization of a rabbit with a recombinant clade B PspC molecule produced antiserum that cross-reacted with both PspC and PspA from 15 pneumococcal isolates. The cross-reactive antibodies afforded cross-protection in a mouse model system. Mice immunized with PspC were protected against challenge with a strain that expressed PspA but not PspC. The PspA-and PspC-cross-reactive antibodies were directed to the proline-rich domain present in both molecules.

No abstract

No abstract