CCL19-CCR7-dependent reverse transendothelial migration of myeloid cells clears Chlamydia muridarum from the arterial intima.

Regions of the normal arterial intima predisposed to atherosclerosis are sites of ongoing monocyte trafficking and also contain resident myeloid cells with features of dendritic cells. However, the pathophysiological roles of these cells are poorly understood. Here we found that intimal myeloid cells underwent reverse transendothelial migration (RTM) into the arterial circulation after systemic stimulation of pattern-recognition receptors (PRRs). This process was dependent on expression of the chemokine receptor CCR7 and its ligand CCL19 by intimal myeloid cells. In mice infected with the intracellular pathogen Chlamydia muridarum, blood monocytes disseminated infection to the intima. Subsequent CCL19-CCR7-dependent RTM was critical for the clearance of intimal C. muridarum. This process was inhibited by hypercholesterolemia. Thus, RTM protects the normal arterial intima, and compromised RTM during atherogenesis might contribute to the intracellular retention of pathogens in atherosclerotic lesions.

α1ß1 integrin-mediated adhesion inhibits macrophage exit from a peripheral inflammatory lesion.

Integrins are adhesion molecules critical for the recruitment of leukocytes from blood into peripheral tissues. However, whether integrins are also involved in leukocyte exit from peripheral tissues via afferent lymphatics to the draining lymph node remains poorly understood. In this article, we show that adhesion by the collagen IV-binding integrin α1ß1 unexpectedly inhibited macrophage exit from inflamed skin. We monitored macrophages exiting mouse footpads using a newly developed in situ pulse labeling technique. Blockade of α1ß1 integrin or genetic deletion (Itga1(-/-)) increased macrophage exit efficiency. Chemotaxis assays through collagen IV showed more efficient migration of Itga1(-/-) macrophages relative to wild type. Given that macrophages are key orchestrators of inflammation, α1ß1 integrin adhesion may represent a mechanism for regulating inflammatory responses by controlling macrophage exit or persistence in inflamed tissues.

Endophthalmitis post complicated cataract surgery associated with Klebsiella pneumoniae.

An 82-year-old woman underwent complicated cataract surgery with subsequent endophthalmitis. She presented with a unique purulent collection with ciliary body involvement and Klebsiella pneumoniae was grown on culture. Klebsiella is a rare cause of endophthalmitis and ciliary body involvement has not previously been reported.

Tracking of leukocyte recruitment into tissues of mice by in situ labeling of blood cells with the fluorescent dye CFDA SE.

Models of inflammatory and immune diseases are extensively studied in mice with engineered genetic mutations, and tracking the recruitment of blood leukocytes into tissues is an important component of these studies. A direct in situ method for labeling the total pool of blood cells in mice by a single intravenous injection of the fluorescent dye CFDA SE (CFSE) is described. The fluorescence intensity of labeled cells initially declines, but remains stable after 4 h, enabling detection weeks after labeling. Labeled leukocytes can be tracked as they accumulate in lymphoid tissues and sites of inflammation and then be immunophenotyped for analysis by flow cytometry. This method is rapid, reproducible and simple to perform.