CCR2 mediates homeostatic and inflammatory release of Gr1(high) monocytes from the bone marrow, but is dispensable for bladder infiltration in bacterial urinary tract infection.

CCR2 is thought to recruit monocytes to sites of infection. Two subpopulations of murine blood monocytes differing in Gr1 and CCR2 expression have been described. The exact role of CCR2 in migration of CCR2(low)Gr1(low) and CCR2(high)Gr1(high) monocytes into nonlymphoid tissue is controversial. In this study, we have addressed this question in a murine model of bacterial urinary tract infection. Only Gr1(high) monocytes were recruited into the infected bladder. CCR2 deficiency reduced their frequency in this organ, indicating a requirement of this chemokine receptor. Importantly, CCR2-deficient mice also showed reduced Gr1(high) monocyte numbers in the blood, but not in the bone marrow (BM), indicating that CCR2 acted at the step of monocyte release into the circulation. The same was found also in noninfected mice, indicating a further involvement of CCR2 in steady-state BM egress. An additional requirement of CCR2 in monocyte recruitment from the blood into the bladder was excluded by tracking particle-labeled endogenous monocytes and by adoptive transfer of BM-derived monocyte subsets. These findings demonstrate that CCR2 governs homeostatic and infection-triggered release of Gr1(high) monocytes from the BM into the blood but is dispensable for recruitment into a nonlymphoid tissue.

T helper type 1 memory cells disseminate postoperative ileus over the entire intestinal tract.

Localized abdominal surgery can lead to disruption of motility in the entire gastrointestinal tract (postoperative ileus). Intestinal macrophages produce mediators that paralyze myocytes, but it is unclear how the macrophages are activated, especially those in unmanipulated intestinal areas. Here we show that intestinal surgery activates intestinal CD103(+)CD11b(+) dendritic cells (DCs) to produce interleukin-12 (IL-12). This promotes interferon-γ (IFN-γ) secretion by CCR9(+) memory T helper type 1 (T(H)1) cells which activates the macrophages. IL-12 also caused some T(H)1 cells to migrate from surgically manipulated sites through the bloodstream to unmanipulated intestinal areas where they induced ileus. Preventing T cell migration with the drug FTY720 or inhibition of IL-12, T-bet (T(H)1-specific T box transcription factor) or IFN-γ prevented postoperative ileus. CCR9(+) T(H)1 memory cells were detected in the venous blood of subjects 1 h after abdominal surgery. These findings indicate that postoperative ileus is a T(H)1 immune-mediated disease and identify potential targets for disease monitoring and therapy.

In vivo visualization of dendritic cells, macrophages, and microglial cells responding to laser-induced damage in the fundus of the eye.

PURPOSE: To study the in vivo response of mononuclear phagocytes (i.e., dendritic cells [DCs] and macrophages [MPhis]) in the posterior eye segment after laser-induced injury, and to gain a better understanding of the role of these cells in inflammatory eye disease. METHODS: CX(3)CR1(GFP/+) knockin mice were used, in which DCs, MPhis, and microglia cells (microGCs) are constitutively fluorescent. These reporter mice were examined by a confocal scanning laser ophthalmoscope (cSLO) after argon laser coagulation. cSLO was complemented by fluorescence microscopy of retinal flatmounts and eye cryosections, to study cell morphology and location, and by multicolor flow cytometry, to determine the number and identity of the fluorescent cells. RESULTS: The retina of healthy reporter mice featured abundant fluorescent microGCs. After laser injury to the fundus, these cells accumulated and migrated laterally toward injury after 60 minutes. Distinctly shaped fluorescent cells accumulated within laser spots and were identified by flow cytometry and immunofluorescence microscopy as DCs and MPhis in the retina and choroid. The DCs rapidly disappeared from the retina, whereas the MPhis stayed longer. Choroidal infiltrates were detectable even 35 days after laser injury, in particular in larger spots resulting from higher laser intensity. In addition, nonfluorescent granulocytes were detected in the choroid. CONCLUSIONS: The synergistic use of ophthalmoscopy, flow cytometry, and immunofluorescence microscopy allows detailed dissection of the in vivo response of mononuclear phagocytes to laser injury of the fundus. The number of microGCs increased in the retina. DCs and MPhis were present in the retina and choroid infiltrate. MPhis and granulocytes persisted in the choroid infiltrate longer than previously thought.

Tumor necrosis factor alpha- and inducible nitric oxide synthase-producing dendritic cells are rapidly recruited to the bladder in urinary tract infection but are dispensable for bacterial clearance.

The role of dendritic cells (DC) in urinary tract infections (UTI) is unknown. These cells contribute directly to the innate defense against various viral and bacterial infections. Here, we studied their role in UTI using an experimental model induced by transurethral instillation of the uropathogenic Escherichia coli (UPEC) strain 536 into C57BL/6 mice. While few DC were found in the uninfected bladder, many had been recruited after 24 h, mostly to the submucosa and uroepithelium. They expressed markers of activation and maturation and exhibited the CD11b+ F4/80+ CD8- Gr-1- myeloid subtype. Also, tumor necrosis factor alpha (TNF-alpha)- and inducible nitric oxide synthase (iNOS)-producing CD11bINT DC (Tip-DC) were detected, which recently were proposed to be critical in the defense against bacterial infections. However, Tip-DC-deficient CCR2-/- mice did not show reduced clearance of UPEC from the infected bladder. Moreover, clearance was also unimpaired in CD11c-DTR mice depleted of all DC by injection of diphtheria toxin. This may be explained by the abundance of granulocytes and of iNOS- and TNF-alpha-producing non-DC that were able to replace Tip-DC functionality. These findings demonstrate that some of the abundant DC recruited in UTI contributed innate immune effector functions, which were, however, dispensable in the microenvironment of the bladder.