Investigation of the role of Streptococcus pneumoniae surface proteins PspA and PspC

S. pneumoniae has a relatively fast growth rate and can reach high cell densities in infections environments and can cause severe diseases, like hemolytic uremic syndrome (HUS). As part of its life cycle, S. pneumoniae remodel the genome by taking up and incorporating of exogenous DNA from other pneumococci or viruses. This can facilitate the spread of antibiotic resistance and evasion of vaccine-induced immunity and makes it necessary to search for novel targets, to understand the diversity, as well as the immune escape strategies of this pathogenic bacterium. S. pneumoniae has developed different strategies to evade or limit complement mediated opsonization and subsequent phagocytosis. Furthermore, sequence variation suggests that the two immune evasion proteins PspA and PspC are important for interaction of pneumococci with the host. Given the multifunctional characteristics and mosaic structure of PspA and PspC, it is important to investigate the domain composition of the proteins among different strains and in particular among clinical isolates. S. pneumoniae can induce pneumococcal hemolytic uremic syndrome (HUS). To characterize the role of HUS inducing strains, we evaluated 48 S. pneumoniae strains isolated from patients. These diseases associated isolates, Sp-HUS show strong complement resistance when challenged with complement active human serum. Sp-HUS strains show lower levels of surface C3 deposition, as compared to a pathogenic, strain D39. Consequently Sp-HUS strains evade host complement rather efficiently. In addition, I show that Sp-HUS strains have specific PspA and PspC variants which include unique domain profiles. By evaluating complement resistance of Sp-HUS, PspA interacting with the human complement regulator C3 and PspC binding with human Factor H together assisted Sp-HUS to resist and evade from the complement.


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