Isogenic fimbriae mutant of P. gingivalis targets Dendritic cell DC-SIGN

Objective: DC-SIGN (CD209), a C-type lectin receptor involved in uptake of bacteria and HIV-1 by dendritic cells (DC) and in the formation of DC-T cell conjugates, is increasingly expressed in chronic periodontitis (CP), but its function in the pathophysiology of CP is unclear. The objective of this study is to determine the role of DC-SIGN in binding and uptake of the periodontal pathogen Porphyromonas gingivalis and its isogenic fimbriae deficient mutants.

Methods: Three previously published and characterized major/minor fimbriae mutants of P. gingivalis and the parent strain 381 (provided courtesy of C.A. Genco) labeled with CFSE were co-cultured at 37oC with immortalized Raji B cells as well as transgenic immortalized Raji B cell lines that constitutively express DC-SIGN, in the presence/absence of cytochalasin D (or on ice) for from 1.5h to 18h. The association of P. gingivalis with the two Raji cell lines, in triplicate, was monitored by FACS analysis and by image enhanced fluorescence microscopy. Positive control species Lactobacillus cassei, previously reported to target DC-SIGN was also used. Anti-DC-SIGN mAb, Ca2+-chelator EDTA as well as carbohydrate competitors to DC-SIGN such as mannan were used to block DC-SIGN and abrogate binding by P. gingivalis and its mutants.

Results: Preliminary results of FACS analysis and fluorescence imaging suggest that one of the fimbriae-deficient mutant strains specifically targets DC-SIGN, a pattern recognition receptor reportedly involved in suppression of P38-MAPK-mediated intracellular signaling and in immunosuppression. Efforts are underway to further characterize the receptor ligand interactions of P.gingivalis, its major/minor fimbriae with DC-SIGN and to determine the immune consequence of interaction of P.gingivalis with DC-SIGN in human monocyte derived DCs.

Conclusion: The data suggest that P. gingivalis may specifically target DC-SIGN, a C-type lectin receptor on dendritic cells reported to suppress intracellular signaling and down-modulate the adaptive immune response