Summary Cardiac macrophages are crucial for tissue repair after cardiac injury but have not been well characterized. Here we identify four populations of cardiac macrophages. At steady state, resident macrophages were primarily maintained through local proliferation. However, after macrophage depletion or during cardiac inflammation, Ly6chi monocytes contributed to all four macrophage populations, whereas resident macrophages also expanded numerically through proliferation. Genetic fate mapping revealed that yolk-sac and fetal monocyte progenitors gave rise to the majority of cardiac macrophages, and the heart was among a minority of organs in which substantial numbers of yolk-sac macrophages persisted in adulthood. CCR2 expression and dependence distinguished cardiac macrophages of adult monocyte versus embryonic origin. Transcriptional and functional data revealed that monocyte-derived macrophages coordinate cardiac inflammation, while playing redundant but lesser roles in antigen sampling and efferocytosis. These data highlight the presence of multiple cardiac macrophage subsets, with different functions, origins and strategies to regulate compartment.

Escherichia coli entry into the bladder is met with potent innate defenses, including neutrophil influx and epithelial exfoliation. Bacterial subversion of innate responses involves invasion into bladder superficial cells. We discovered that the intracellular bacteria matured into biofilms, creating pod-like bulges on the bladder surface. Pods contained bacteria encased in a polysaccharide-rich matrix surrounded by a protective shell of uroplakin. Within the biofilm, bacterial structures interacted extensively with the surrounding matrix, and biofilm associated factors had regional variation in expression. The discovery of intracellular biofilm-like pods explains how bladder infections can persist in the face of robust host defenses.

The vast majority of urinary tract infections are caused by strains of uropathogenic Escherichia coli that encode filamentous adhesive organelles called type 1 pili. These structures mediate both bacterial attachment to and invasion of bladder epithelial cells. However, the mechanism by which type 1 pilus-mediated bacterial invasion contributes to the pathogenesis of a urinary tract infection is unknown. Here we show that type 1-piliated uropathogens can invade the superficial epithelial cells that line the lumenal surface of the bladder and subsequently replicate, forming massive foci of intracellular E. coli termed bacterial factories. In response to infection, superficial bladder cells exfoliate and are removed with the flow of urine. To avoid clearance by exfoliation, intracellular uropathogens can reemerge and eventually establish a persistent, quiescent bacterial reservoir within the bladder mucosa that may serve as a source for recurrent acute infections. These observations suggest that urinary tract infections are more chronic and invasive than generally assumed.Uropathogenic Escherichia coli (UPEC), the primary cause of urinary tract infections (UTIs) (16,35), is not generally regarded as an invasive pathogen. Infections caused by UPEC are typically self-limiting and UPEC rarely spreads beyond the urinary tract (17,35). Adherence of UPEC to host epithelial cells within the bladder and other tissues within the urinary tract is considered critical to the ability of UPEC to cause disease (2, 12, 33). Filamentous adhesive organelles called type 1 pili, which are encoded by virtually all UPEC isolates (25), can mediate bacterial attachment to host bladder cells and have been shown to be significant virulence factors associated with UTIs (6,24,25,29,37). These structures contain an adhesin molecule, FimH, that binds mannose-containing glycoprotein receptors expressed on the lumenal surface of the bladder (23,38). In addition to mediating bacterial attachment, recent work has shown that the FimH adhesin can also directly stimulate host cell signaling cascades that lead to the induction of cytoskeletal rearrangements and the envelopment and internalization of adherent UPEC (27). These findings have suggested that the invasion of bladder epithelial cells by type 1-piliated UPEC may have an as-yet-appreciated role in the pathogenesis of UTIs.Data from various experimental systems indicate that invasion of eukaryotic cells can provide bacterial pathogens refuge from both innate and adaptive host defenses and may also facilitate the dissemination of microbes within and across tissue barriers (8). Within the urinary tract, the bladder epithelium functions as a formidable physical barrier, preventing the diffusion of urine and other substances from within the bladder lumen (15, 26). The bladder epithelium, which is composed of a single layer of large, highly differentiated superficial cells overlying two or three layers of small, relatively undifferentiated basal and intermediate epithelial cells, also serves as an a...

Significance This study addresses a fundamentally important and widely debated issue in the field of inflammation, which is why inflammation can be simultaneously deleterious after injury and yet is essential for tissue repair. Recently, an important new paradigm has emerged in the macrophage field: Organs are replete with resident macrophages of embryonic origin, distinct from monocyte-derived macrophages. In this article, we use a new model of cardiac injury and show that distinct macrophage populations derived from embryonic and adult lineages are important determinants of tissue repair and inflammation, respectively. Our data suggest that therapeutics, which inhibit monocyte-derived macrophages and/or selectively harness the function of embryonic-derived macrophages, may serve as novel treatments for heart failure.

contributed equally to this work Most strains of uropathogenic Escherichia coli (UPEC) encode ®lamentous adhesive organelles called type 1 pili. We have determined that the type 1 pilus adhesin, FimH, mediates not only bacterial adherence, but also invasion of human bladder epithelial cells. In contrast, adherence mediated by another pilus adhesin, PapG, did not initiate bacterial internalization. FimH-mediated invasion required localized host actin reorganization, phosphoinositide 3-kinase (PI 3-kinase) activation and host protein tyrosine phosphorylation, but not activation of Src-family tyrosine kinases. Phosphorylation of focal adhesin kinase (FAK) at Tyr397 and the formation of complexes between FAK and PI 3-kinase and between a-actinin and vinculin were found to correlate with type 1 pilus-mediated bacterial invasion. Inhibitors that prevented bacterial invasion also blocked the formation of these complexes. Our results demonstrate that UPEC strains are not strictly extracellular pathogens and that the type 1 pilus adhesin FimH can directly trigger host cell signaling cascades that lead to bacterial internalization.