In many pathogens CPS has been found to be involved in evasion of the host immune system by circumvention of phagocytosis, opsonization and complement killing [15–17]. The aim of this study was to investigate in vitro differences in host response during infection with a wild type and an isogenic non-encapsulated mutant of a naturally encapsulated strain. The well-studied K1 serotype W83 strain was used as the wild type strain since its CPS biosynthesis locus has been described [18, 19]. An insertional mutation in PG0120 (epsC) was constructed, which yielded a non-encapsulated Proteases inhibitor strain. The gene has been annotated as a UDP-GlcNAc 2-epimerase.

This epsC mutant is tested in a fibroblast infection model [20] since fibroblasts are the most abundant stromal cells in soft connective tissue of the gingiva [21] and among the first cells encountering periodontal infections by anaerobic

bacteria like P. gingivalis. And above all, fibroblasts have been shown to be involved in the immune response in periodontitis [22, 23]. Human gingival fibroblasts were infected with W83 and the epsC mutant and transcription of IL-1β, IL-6 and IL-8 was determined as host response parameters. p38 inhibitors clinical trials This study provides the first direct evidence that P. gingivalis CPS reduces the host immune response, thereby potentially enabling evasion of the immune system to sustain successful long-term infection. Results EpsC mutant construction After

transformation of the linearized plasmid pΔEpsC to P. gingivalis W83 the epsC insertional mutation was confirmed by specific PCR amplifications and agarose gel electrophoresis of the products (data not shown). Primer combinations epsC BamHI F × PG0119 R and EryF F × epsC EcoRI R (Table 1) ensured that a 1.2 Kb fragment of Dichloromethane dehalogenase pΔEpsC had been integrated by double crossover at PG0120 (epsC) as expected, replacing the intact copy with the insertionally inactivated copy (Figure 1). Table 1 Primers used in this study Target Name Sequence (5′-3′) epsC epsC BamHI F ATATAGGATCCATGAAAAAAGTGATGTTGGTC   epsC EcoRI R CTATGAATTCATCTTCGGCTAAATGCATCG   epsC AscI F GAATATAGGCGCGCCATGAAAAAAGTGATGTTGGTC   epsC SpeI CTATACTAGTATCTTCGGCTAAATGCATCG eryF eryF ClaI F CCACCATCGATCGATAGCTTCCGCTATTGC   eryF ClaI R CCACCATCGATGTTTCCGCTCCATCGCCAATTTGC CP25 CP25 ClaI F GCCATATCGATGCATGCGGATCCCATTATG   CP25 AscI R CCTTTAGGCGCGCCCTTAATTTCTCCTC IL-6 IL-6 F GGCACTGGCAGAAAACAACC   IL-6 R GGCAAGTCTCCTCATTGAATCC IL-8 IL-8 F GGCAGCCTTCCTGATTTCTG   IL-8 R CTGACACATCTAAGTTCTTCTTTAGCACTCCTT IL-1β IL-1β F AAGATTCAGGTTTACTCACGTC   IL-1β R TGATGCTGCTTACATGTCTCG hup-1 hup-1 F GAAAAGGCCAACCTCACAAA   hup-1 F TCCGATGAGAGCGATTTTCT glk glk F ATGAATCCGATCCGCCACCAC   glk R GCCTCCCATCCCAAAGCACT In bold: restriction sites used in this study Figure 1 Schematic representation of the knockout strategy to construct the epsC insertional mutation in W83. A.