Endosomal recognition of Lactococcus lactis G121 and its RNA by dendritic cells is key to its allergy-protective effects.

BACKGROUND: Bacterial cowshed isolates are allergy protective in mice; however, the underlying mechanisms are largely unknown. We examined the ability of Lactococcus lactis G121 to prevent allergic inflammatory reactions. OBJECTIVE: We sought to identify the ligands and pattern recognition receptors through which L lactis G121 confers allergy protection. METHODS: L lactis G121-induced cytokine release and surface expression of costimulatory molecules by untreated or inhibitor-treated (bafilomycin and cytochalasin D) human monocyte-derived dendritic cells (moDCs), bone marrow-derived mouse dendritic cells (BMDCs), and moDC/naive CD4+ T-cell cocultures were analyzed by using ELISA and flow cytometry. The pathology of ovalbumin-induced acute allergic airway inflammation after adoptive transfer of BMDCs was examined by means of microscopy. RESULTS: L lactis G121-treated murine BMDCs and human moDCs released TH1-polarizing cytokines and induced TH1 T cells. Inhibiting phagocytosis and endosomal acidification in BMDCs or moDCs impaired the release of TH1-polarizing cytokines, costimulatory molecule expression, and T-cell activation on L lactis G121 challenge. In vivo allergy protection mediated by L lactis G121 was dependent on endosomal acidification in dendritic cells (DCs). Toll-like receptor (Tlr) 13-/- BMDCs showed a weak response to L lactis G121 and were unresponsive to its RNA. The TH1-polarizing activity of L lactis G121-treated human DCs was blocked by TLR8-specific inhibitors, mediated by L lactis G121 RNA, and synergistically enhanced by activation of nucleotide-binding oligomerization domain-containing protein (NOD) 2. CONCLUSION: Bacterial RNA is the main driver of L lactis G121-mediated protection against experimentally induced allergy and requires both bacterial uptake by DCs and endosomal acidification. In mice L lactis G121 RNA signals through TLR13; however, the most likely intracellular receptor in human subjects is TLR8.

Biological effects of carbon black nanoparticles are changed by surface coating with polycyclic aromatic hydrocarbons.

BACKGROUND: Carbon black nanoparticles (CBNP) are mainly composed of carbon, with a small amount of other elements (including hydrogen and oxygen). The toxicity of CBNP has been attributed to their large surface area, and through adsorbing intrinsically toxic substances, such as polycyclic aromatic hydrocarbons (PAH). It is not clear whether a PAH surface coating changes the toxicological properties of CBNP by influencing their physicochemical properties, through the specific toxicity of the surface-bound PAH, or by a combination of both. METHODS: Printex®90 (P90) was used as CBNP; the comparators were P90 coated with either benzo[a]pyrene (BaP) or 9-nitroanthracene (9NA), and soot from acetylene combustion that bears various PAHs on the surface (AS-PAH). Oxidative stress and IL-8/KC mRNA expression were determined in A549 and bronchial epithelial cells (16HBE14o-, Calu-3), mouse intrapulmonary airways and tracheal epithelial cells. Overall toxicity was tested in a rat inhalation study according to Organization for Economic Co-operation and Development (OECD) criteria. Effects on cytochrome monooxygenase (Cyp) mRNA expression, cell viability and mucociliary clearance were determined in acute exposure models using explanted murine trachea. RESULTS: All particles had similar primary particle size, shape, hydrodynamic diameter and ζ-potential. All PAH-containing particles had a comparable specific surface area that was approximately one third that of P90. AS-PAH contained a mixture of PAH with expected higher toxicity than BaP or 9NA. PAH-coating reduced some effects of P90 such as IL-8 mRNA expression and oxidative stress in A549 cells, granulocyte influx in the in vivo OECD experiment, and agglomeration of P90 and mucus release in the murine trachea ex vivo. Furthermore, P90-BaP decreased particle transport speed compared to P90 at 10 µg/ml. In contrast, PAH-coating induced IL-8 mRNA expression in bronchial epithelial cell lines, and Cyp mRNA expression and apoptosis in tracheal epithelial cells. In line with the higher toxicity compared to P90-BaP and P90-9NA, AS-PAH had the strongest biological effects both ex vivo and in vivo. CONCLUSIONS: Our results demonstrate that the biological effect of CBNP is determined by a combination of specific surface area and surface-bound PAH, and varies in different target cells.

Interleukin-21 inhibits dendritic cell-mediated T cell activation and induction of contact hypersensitivity in vivo.

Interleukin (IL)-21 is a newly described cytokine that is produced by activated T cells and displays structural homology to IL-4 and IL-15. We here analyzed the role of IL-21 in dendritic cell (DC)-induced, T cell-mediated contact hypersensitivity (CHS) in vivo and on T cell activation and unspecific mixed lymphocyte reaction in vitro. By PCR, we demonstrate here constitutive expression of the specific IL-21 receptor and the common gamma-chain in DC, which together are able to mediate IL-21 signaling. Short-time incubation of in vitro generated DC with IL-21 significantly reduced their potential to induce an antigen-specific CD8+ T cell proliferation. Interestingly, 2h incubation of these DC with IL-21 before injection completely inhibited the potential of these DC to induce a CHS reaction to the hapten fluorescein 5-isothiocyanate in vivo. Mice injected with IL-21-treated DC even failed to mount a CHS response after repetitive injection of non-IL-21-treated DC 2 weeks later, suggesting that an antigen-specific unresponsiveness can be induced by IL-21-treated DC. Our data demonstrate that IL-21 is a new modulator of DC-T cell interaction with the potential to induce DC-mediated antigen-specific tolerance.

Differential regulation of mast cell degranulation versus cytokine secretion by the actin regulatory proteins Coronin1a and Coronin1b.

Mast cell (MC) activation via aggregation of the high affinity IgE receptor (FcεRI) causes degranulation and release of proinflammatory mediators in a process that involves the reorganization of the actin cytoskeleton. However, the regulatory pathways and the molecular links between cytoskeletal changes and MC function are incompletely understood. In this study, we provide genetic evidence for a critical role of the actin-regulatory proteins Coronin1a (Coro1a) and Coro1b on exocytic pathways in MCs: Coro1a(-/-) bone marrow-derived MCs exhibit increased FcεRI-mediated degranulation of secretory lysosomes but significantly reduced secretion of cytokines. Hyperdegranulation of Coro1a(-/-) MCs is further augmented by the additional loss of Coro1b. In vivo, Coro1a(-/-)Coro1b(-/-) mice displayed enhanced passive cutaneous anaphylaxis. Functional reconstitution assays revealed that the inhibitory effect of Coro1a on MC degranulation strictly correlates with cortical localization of Coro1a, requires its filamentous actin-binding activity, and is regulated by phosphorylation of Ser2 of Coro1a. Thus, coronin proteins, and in turn the actin cytoskeleton, exhibit a functional dichotomy as differential regulators of degranulation versus cytokine secretion in MC biology.