Targeting of DC-SIGN on Human Dendritic Cells by Minor Fimbriated Porphyromonas gingivalis Strains Elicits a Distinct Effector T Cell Response

Abstract

The oral mucosal pathogen Porphyromonas gingivalis expresses at least two adhesins: the 67-kDa mfa-1 (minor) fimbriae and the 41-kDa fimA (major) fimbriae. In periodontal disease, P. gingivalis associates in situ with dermal dendritic cells (DCs), many of which express DC-SIGN (DC-specific ICAM-3 grabbing nonintegrin; CD209). The cellular receptors present on DCs that are involved in the uptake of minor/major fimbriated P. gingivalis, along with the effector immune response induced, are presently unclear. In this study, stably transfected human DC-SIGN+/− Raji cell lines and monocyte-derived DCs (MoDCs) were pulsed with whole, live, wild-type Pg381 or isogenic major (DPG-3)-, minor (MFI)-, or double fimbriae (MFB)-deficient mutant P. gingivalis strains. The influence of blocking Abs, carbohydrates, full-length glycosylated HIV-1 gp120 envelope protein, and cytochalasin D on the uptake of strains and on the immune responses was determined in vitro. We show that the binding of minor fimbriated P. gingivalis strains to Raji cells and MoDCs is dependent on DC-SIGN, whereas the double fimbriae mutant strain does not bind. Binding to DC-SIGN on MoDCs is followed by the internalization of P. gingivalis into DC-SIGN-rich intracellular compartments, and MoDCs secrete low levels of inflammatory cytokines and remain relatively immature. Blocking DC-SIGN with HIV-1 gp120 prevents the uptake of minor fimbriated strains and deregulates the expression of inflammatory cytokines. Moreover, MoDCs promote a Th2 or Th1 effector response, depending on whether they are pulsed with minor or major fimbriated P. gingivalis strains, respectively, suggesting distinct immunomodulatory roles for the two adhesins of P. gingivalis.

The Native 67-Kilodalton Minor Fimbria of Porphyromonas gingivalis Is a Novel Glycoprotein with DC-SIGN-Targeting Motifs

“…Our previously published work established that the minor fimbria is necessary for targeting DC-SIGN, resulting in entry of P. gingivalis into DCs (68). We were able to abrogate minor fimbria-mediated DC-SIGN ligation by using DC-SIGN-blocking agents or agonists, including fucose, mannose, and mannan (68).…”

“…The isogenic, major fimbria-deficient mutant DPG3, which expresses only the minor fimbria (Pg min ϩ /maj Ϫ ), was maintained anaerobically (10% H 2 , 10% CO 2 , 80% N 2 ) in a Forma Scientific anaerobic system glove box, model 1025/1029, at 37°C in Difco anaerobe broth MIC. Erythromycin (5 g/ml) was added according to the selection requirements of the strain (11,20,54,68). Fimbriae were purified as described by Davey et al (11).…”

“…We were able to abrogate minor fimbria-mediated DC-SIGN ligation by using DC-SIGN-blocking agents or agonists, including fucose, mannose, and mannan (68). Additionally, we described that the minor fimbria is able to induce immunosuppression of DCs via its interaction with DC-SIGN, which was blocked by sugars (68).…”

“…This interaction might aid in P. gingivalis colonization of plaque biofilm before it invades gingival tissue (26,41). We recently showed that the minor fimbria targets DC-SIGN on DCs for entry into DCs and that this targeting has the immunological consequence of dampening the immune response (68).…”

“…Additionally, we described that the minor fimbria is able to induce immunosuppression of DCs via its interaction with DC-SIGN, which was blocked by sugars (68). Further, we demonstrated that minor fimbriated strains of P. gingivalis inhibited DC maturation and suppressed proinflammatory cytokine secretion (68). Moreover, DCs that were pulsed with minor fimbriated strains of P. gingivalis and then cocultured with autologous T cells shifted the T-cell effector phenotype to a Th2 effector phenotype, as evidenced by high interleukin-4 (IL-4) production (68).…”