[Show abstract][Hide abstract] ABSTRACT: M2 macrophages suppress inflammation in numerous disorders, including tumour formation, infection and obesity. However, the exact role of M2 macrophages in the context of several other diseases is still largely undefined. We here show that human M2 macrophages promote inflammation instead of suppressing inflammation on simultaneous exposure to complexed IgG (c-IgG) and TLR ligands, as occurs in the context of diseases such as rheumatoid arthritis (RA). c-IgG-TLR ligand co-stimulation of M2 macrophages selectively amplifies production of pro-inflammatory cytokines TNF-α, IL-1β and IL-6 and promotes Th17 responses, which all play a critical role in RA pathology. Induction of pro-inflammatory cytokines on c-IgG co-stimulation mainly depends on Fc gamma receptor IIa (FcγRIIa), which selectively amplifies cytokine gene transcription and induces caspase-1 activation. These data indicate that FcγR-TLR cross-talk may be targeted for treatment to attenuate inflammation in RA, by restoring the anti-inflammatory function of M2 macrophages.
[Show abstract][Hide abstract] ABSTRACT: The mechanisms preventing detrimental T-cell responses against commensal skin bacteria remain elusive. Using monocyte-derived and skin-derived dendritic cells (DCs), we demonstrate that epidermal Langerhans cells (LCs), the DCs in the most superficial layer of the skin, have a poor capacity to internalize bacteria because of low expression of FcγRIIa. Furthermore, LCs show deficiency in processing and major histocompatibility complex II (MHC-II)-restricted presentation of bacterial antigens, as a result of a decreased expression of molecules involved in these functionalities. The reduced capacity to take up, process, and present bacterial antigens cannot be restored by LC activation by ectopically expressed Toll-like receptors or by cytokines. Consequently, bacteria-primed LCs poorly restimulate antibacterial memory CD4(+) T cells and inefficiently induce bacteria-specific effector CD4(+) T cells from naive T cells; however, they initiate the development of regulatory Foxp3(+)CD4(+) T cells, which are able to suppress the proliferation of autologous bystander T cells specific for the same bacteria. In contrast, dermal DCs that reside in the deeper dermal layer of the skin efficiently present bacterial antigens and provoke robust antibacterial naive and memory CD4(+) T-cell responses. In conclusion, LCs form a unique DC subset that is adapted at multiple levels for the maintenance of tolerance to bacterial skin flora.Journal of Investigative Dermatology advance online publication, 7 February 2013; doi:10.1038/jid.2012.500.
Journal of Investigative Dermatology 02/2013; · 6.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dendritic cells (DCs) are essential in inducing adaptive immune responses against bacteria by expressing cytokines that skew T-cell responses toward protective Th17 cells. Although it is widely recognized that induction of these cytokines by DCs involves activation of multiple receptors, it is still incompletely characterized which combination of receptors specifically skews Th17-cell responses. Here we have identified a novel role for FcγRIIa in promoting human Th17 cells. Activation of DCs by bacteria opsonized by serum IgG strongly promoted Th17 responses, which was FcγRIIa-dependent and coincided with enhanced production of selected cytokines by DCs, including Th17-promoting IL-1β and IL-23. Notably, FcγRIIa stimulation on DCs did not induce cytokine production when stimulated individually, but selectively amplified cytokine responses through synergy with TLR2, 4, or 5. Importantly, this synergy is mediated at 2 different levels. First, TLR-FcγRIIa costimulation strongly increased transcription of pro-IL-1β and IL-23p19. Second, FcγRIIa triggering induced activation of caspase-1, which cleaves pro-IL-1β into its bioactive form and thereby enhanced IL-1β secretion. Taken together, these data identified cross-talk between TLRs and FcγRIIa as a novel mechanism by which DCs promote protective effector Th17-cell responses against bacteria.
[Show abstract][Hide abstract] ABSTRACT: IL-17-producing CD4(+) T helper (Th17) cells are important for immunity against extracellular pathogens and in autoimmune diseases. The factors that drive Th17 development in human remain a matter of debate. Here we show that, compared with classic CD28 costimulation, alternative costimulation via the CD5 or CD6 lymphocyte receptors forms a superior pathway for human Th17-priming. In the presence of the Th17-promoting cytokines IL-1β, IL-6, IL-23, and transforming growth factor-β (TGF-β), CD5 costimulation induces more Th17 cells that produce higher amounts of IL-17, which is preceded by prolonged activation of signal transducer and activator of transcription 3 (STAT3), a key regulator in Th17 differentiation, and enhanced levels of the IL-17-associated transcription factor retinoid-related orphan receptor-γt (ROR-γt). Strikingly, these Th17-promoting signals critically depend on CD5-induced elevation of IL-23 receptor (IL-23R) expression. The present data favor the novel concept that alternative costimulation via CD5, rather than classic costimulation via CD28, primes naive T cells for stable Th17 development through promoting the expression of IL-23R.
[Show abstract][Hide abstract] ABSTRACT: How the development of antibacterial T helper 17 (Th17) cells is selectively promoted by antigen-presenting dendritic cells (DCs) is unclear. We showed that bacteria, but not viruses, primed human DCs to promote IL-17 production in memory Th cells through the nucleotide oligomerization domain 2 (NOD2)-ligand muramyldipeptide (MDP), a derivative of bacterial peptidoglycan. MDP enhanced obligate bacterial Toll-like receptor (TLR) agonist induction of IL-23 and IL-1, which promoted IL-17 expression in T cells. The role of NOD2 in this IL-23-IL-1-IL-17 axis could be confirmed in NOD2-deficient DCs, such as DCs from selected Crohn's disease patients. Thus, antibacterial Th17-mediated immunity in humans is orchestrated by DCs upon sensing bacterial NOD2-ligand MDP.