No abstract

Porphyromonas gingivalis, a Gram-negative bacterium that causes periodontitis, activates the kinin system via the cysteine protease R-gingipain. Using a model of buccal infection based on P. gingivalis inoculation in the anterior mandibular vestibule, we studied whether kinins released by gingipain may link mucosal inflammation to T cell-dependent immunity through the activation of bradykinin B2 receptors (B2R). Our data show that P. gingivalis W83 (wild type), but not gingipain-deficient mutant or wild-type bacteria pretreated with gingipain inhibitors, elicited buccal edema and gingivitis in BALB/c or C57BL/6 mice. Studies in TLR2−/−, B2R−/−, and neutrophil-depleted C57BL/6 mice revealed that P. gingivalis induced edema through the sequential activation of TLR2/neutrophils, with the initial plasma leakage being amplified by gingipain-dependent release of vasoactive kinins from plasma-borne kininogens. We then used fimbriae (Fim) Ag as a readout to verify whether activation of the TLR2→PMN→B2R axis (where PMN is polymorphonuclear neutrophil) at early stages of mucosal infection had impact on adaptive immunity. Analyzes of T cell recall responses indicated that gingipain drives B2R-dependent generation of IFN-γ-producing Fim T cells in submandibular draining lymph nodes of BALB/c and C57BL/6 mice, whereas IL-17-producing Fim T cells were generated only in BALB/c mice. In summary, our studies suggest that two virulence factors, LPS (an atypical TLR2 ligand) and gingipain, forge a trans-cellular cross-talk between TLR2 and B2R, thus forming an innate axis that guides the development of Fim-specific T cells in mice challenged intrabuccally by P. gingivalis. Ongoing research may clarify whether kinin-driven modulation of T cell responses may also influence the severity of chronic periodontitis.

In this paper we report a qualitative morphological analysis of Wallerian degeneration in a marsupial. Right optic nerves of opossums Didelphis marsupialis were crushed with a fine forceps and after 24, 48, 72, 96 and 168 hours the animals were anaesthetized and perfused with fixative. The optic nerves were immersed in fixative and processed for routine transmission electron microscopy. Among the early alterations typical of axonal degeneration, we observed nerve fibers with focal degeneration of the axoplasmic cytoskeleton, watery degeneration and dark degeneration, the latter being prevalent at 168 hours after crush. Our results point to a gradual disintegration of the axoplasmic cytoskeleton, opposed to the previous view of an "all-or-nothing" process . We also report that, due to an unknown mechanism, fibers show either a dark or watery pattern of axonal degeneration, as observed in axon profiles. We also observed fibers undergoing early myelin breakdown in the absence of axonal alterations.

No abstract

Wallerian degeneration (WD) comprises a series of events that includes activation of non-neuronal cells and recruitment of immune cells, creating an inflammatory milieu that leads to extensive nerve fragmentation and subsequent clearance of the myelin debris, both of which are necessary prerequisites for effective nerve regeneration. Previously, we documented accelerated axon regeneration in animals lacking galectin-3 (Gal-3), a molecule associated with myelin clearance. To clarify the mechanisms underlying this enhanced regeneration, we focus here on the early steps of WD following sciatic nerve crush in Gal-3(-/-) mice. Using an in vivo model of nerve degeneration, we observed that removal of myelin debris is more efficient in Gal-3(-/-) than in wild-type (WT) mice; we next used an in vitro phagocytosis assay to document that the phagocytic potential of macrophages and Schwann cells was enhanced in the Gal-3(-/-) mice. Moreover, both RNA and protein levels for the pro-inflammatory cytokines IL-1β and TNF-α, as well as for Toll-like receptor (TLR)-2 and -4, show robust increases in injured nerves from Gal-3(-/-) mice compared to those from WT mice. Collectively, these data indicate that the lack of Gal-3 results in an augmented inflammatory profile that involves the TLR-cytokine pathway, and increases the phagocytic capacity of Schwann cells and macrophages, which ultimately contributes to speeding the course of WD.