CD103+ Kidney Dendritic Cells Protect against Crescentic GN by Maintaining IL-10-Producing Regulatory T Cells.

Kidney dendritic cells (DCs) regulate nephritogenic T cell responses. Most kidney DCs belong to the CD11b+ subset and promote crescentic GN (cGN). The function of the CD103+ subset, which represents <5% of kidney DCs, is poorly understood. We studied the role of CD103+ DCs in cGN using several lines of genetically modified mice that allowed us to reduce the number of these cells. In all lines, we detected a reduction of FoxP3+ intrarenal regulatory T cells (Tregs), which protect against cGN. Mice lacking the transcription factor Batf3 had a more profound reduction of CD103+ DCs and Tregs than did the other lines used, and showed the most profound aggravation of cGN. The conditional reduction of CD103+ DC numbers by 50% in Langerin-DTR mice halved Treg numbers, which did not suffice to significantly aggravate cGN. Mice lacking the cytokine Flt3L had fewer CD103+ DCs and Tregs than Langerin-DTR mice but exhibited milder cGN than did Batf3-/- mice presumably because proinflammatory CD11b+ DCs were somewhat depleted as well. Conversely, Flt3L supplementation increased the number of CD103+ DCs and Tregs, but also of proinflammatory CD11b+ DCs. On antibody-mediated removal of CD11b+ DCs, Flt3L supplementation ameliorated cGN. Mechanistically, CD103+ DCs caused cocultured T cells to differentiate into Tregs and produced the chemokine CCL20, which is known to attract Tregs into the kidney. Our findings show that CD103+ DCs foster intrarenal FoxP3+ Treg accumulation, thereby antagonizing proinflammatory CD11b+ DCs. Thus, increasing CD103+ DC numbers or functionality might be advantageous in cGN.

CX3CR1 reduces kidney fibrosis by inhibiting local proliferation of profibrotic macrophages.

A dense network of macrophages and dendritic cells (DC) expressing the chemokine receptor CX3CR1 populates most tissues. We recently reported that CX3CR1 regulates the abundance of CD11c(+) DC in the kidney and thereby promotes renal inflammation in glomerulonephritis. Given that chronic inflammation usually causes fibrosis, we hypothesized that CX3CR1 deficiency should attenuate renal fibrosis. However, when we tested this hypothesis using the DC-independent murine fibrosis model of unilateral ureteral obstruction, kidney fibrosis was unexpectedly more severe, despite less intrarenal inflammation. Two-photon imaging and flow cytometry revealed in kidneys of CX3CR1-deficient mice more motile Ly6C/Gr-1(+) macrophages. Flow cytometry verified that renal macrophages were more abundant in the absence of CX3CR1 and produced more of the key profibrotic mediator, TGF-ß. Macrophages accumulated because of higher intrarenal proliferation, despite reduced monocyte recruitment and higher signs of apoptosis within the kidney. These findings support the theory that tissue macrophage numbers are regulated through local proliferation and identify CX3CR1 as a regulator of such proliferation. Thus, CX3CR1 inhibition should be avoided in DC-independent inflammatory diseases because it may promote fibrosis.

VEGF-production by CCR2-dependent macrophages contributes to laser-induced choroidal neovascularization.

Age-related macular degeneration (AMD) is the most prevalent cause of blindness in the elderly, and its exsudative subtype critically depends on local production of vascular endothelial growth factor A (VEGF). Mononuclear phagocytes, such as macrophages and microglia cells, can produce VEGF. Their precursors, for example monocytes, can be recruited to sites of inflammation by the chemokine receptor CCR2, and this has been proposed to be important in AMD. To investigate the role of macrophages and CCR2 in AMD, we studied intracellular VEGF content in a laser-induced murine model of choroidal neovascularisation. To this end, we established a technique to quantify the VEGF content in cell subsets from the laser-treated retina and choroid separately. 3 days after laser, macrophage numbers and their VEGF content were substantially elevated in the choroid. Macrophage accumulation was CCR2-dependent, indicating recruitment from the circulation. In the retina, microglia cells were the main VEGF+ phagocyte type. A greater proportion of microglia cells contained VEGF after laser, and this was CCR2-independent. On day 6, VEGF-expressing macrophage numbers had already declined, whereas numbers of VEGF+ microglia cells remained increased. Other sources of VEGF detectable by flow cytometry included in dendritic cells and endothelial cells in both retina and choroid, and Müller cells/astrocytes in the retina. However, their VEGF content was not increased after laser. When we analyzed flatmounts of laser-treated eyes, CCR2-deficient mice showed reduced neovascular areas after 2 weeks, but this difference was not evident 3 weeks after laser. In summary, CCR2-dependent influx of macrophages causes a transient VEGF increase in the choroid. However, macrophages augmented choroidal neovascularization only initially, presumably because VEGF production by CCR2-independent eye cells prevailed at later time points. These findings identify macrophages as a relevant source of VEGF in laser-induced choroidal neovascularization but suggest that the therapeutic efficacy of CCR2-inhibition might be limited.

Exclusive CX3CR1 dependence of kidney DCs impacts glomerulonephritis progression.

DCs and macrophages both express the chemokine receptor CX3CR1. Here we demonstrate that its ligand, CX3CL1, is highly expressed in the murine kidney and intestine. CX3CR1 deficiency markedly reduced DC numbers in the healthy and inflamed kidney cortex, and to a lesser degree in the kidney medulla and intestine, but not in other organs. CX3CR1 also promoted influx of DC precursors in crescentic glomerulonephritis, a DC-dependent aggressive type of nephritis. Disease severity was strongly attenuated in CX3CR1-deficient mice. Primarily CX3CR1-dependent DCs in the kidney cortex processed antigen for the intrarenal stimulation of T helper cells, a function important for glomerulonephritis progression. In contrast, medullary DCs played a specialized role in inducing innate immunity against bacterial pyelonephritis by recruiting neutrophils through rapid chemokine production. CX3CR1 deficiency had little effect on the immune defense against pyelonephritis, as medullary DCs were less CX3CR1 dependent than cortical DCs and because recruited neutrophils produced chemokines to compensate for the DC paucity. These findings demonstrate that cortical and medullary DCs play specialized roles in their respective kidney compartments. We identify CX3CR1 as a potential therapeutic target in glomerulonephritis that may involve fewer adverse side effects, such as impaired anti-infectious defense or compromised DC functions in other organs.