John M. Craig

Patients with familial adenomatous polyposis harbor colonic biofilms containing tumorigenic bacteria

Biofilms provide refuge for cancerous bacteria Familial adenomatous polyposis (FAP) causes benign polyps along the colon. If left untreated, FAP leads to a high incidence of colon cancer. To understand how polyps influence tumor formation, Dejea et al. examined the colonic mucosa of FAP patients. They discovered biofilms containing the carcinogenic versions of the bacterial species Escherichia coli and Bacteroides fragilis. Colon tissue from FAP patients exhibited greater expression of two bacterial genes that produce secreted oncotoxins. Studies in mice showed that specific bacteria could work together to induce colon inflammation and tumor formation. Science, this issue p. 592 Bacterial biofilms are linked to colon cancer. Individuals with sporadic colorectal cancer (CRC) frequently harbor abnormalities in the composition of the gut microbiome; however, the microbiota associated with precancerous lesions in hereditary CRC remains largely unknown. We studied colonic mucosa of patients with familial adenomatous polyposis (FAP), who develop benign precursor lesions (polyps) early in life. We identified patchy bacterial biofilms composed predominately of Escherichia coli and Bacteroides fragilis. Genes for colibactin (clbB) and Bacteroides fragilis toxin (bft), encoding secreted oncotoxins, were highly enriched in FAP patients’ colonic mucosa compared to healthy individuals. Tumor-prone mice cocolonized with E. coli (expressing colibactin), and enterotoxigenic B. fragilis showed increased interleukin-17 in the colon and DNA damage in colonic epithelium with faster tumor onset and greater mortality, compared to mice with either bacterial strain alone. These data suggest an unexpected link between early neoplasia of the colon and tumorigenic bacteria.

Enhanced resolution of experimental ARDS through IL-4-mediated lung macrophage reprogramming.

Despite intense investigation, acute respiratory distress syndrome (ARDS) remains an enormous clinical problem for which no specific therapies currently exist. In this study, we used intratracheal lipopolysaccharide or Pseudomonas bacteria administration to model experimental acute lung injury (ALI) and to further understand mediators of the resolution phase of ARDS. Recent work demonstrates macrophages transition from a predominant proinflammatory M1 phenotype during acute inflammation to an anti-inflammatory M2 phenotype with ALI resolution. We tested the hypothesis that IL-4, a potent inducer of M2-specific protein expression, would accelerate ALI resolution and lung repair through reprogramming of endogenous inflammatory macrophages. In fact, IL-4 treatment was found to offer dramatic benefits following delayed administration to mice subjected to experimental ALI, including increased survival, accelerated resolution of lung injury, and improved lung function. Expression of the M2 proteins Arg1, FIZZ1, and Ym1 was increased in lung tissues following IL-4 treatment, and among macrophages, FIZZ1 was most prominently upregulated in the interstitial subpopulation. A similar trend was observed for the expression of macrophage mannose receptor (MMR) and Dectin-1 on the surface of alveolar macrophages following IL-4 administration. Macrophage depletion or STAT6 deficiency abrogated the therapeutic effect of IL-4. Collectively, these data demonstrate that IL-4-mediated therapeutic macrophage reprogramming can accelerate resolution and lung repair despite delayed use following experimental ALI. IL-4 or other therapies that target late-phase, proresolution pathways may hold promise for the treatment of human ARDS.

Recruited monocytes modulate malaria‐induced lung injury through CD36‐mediated clearance of sequestered infected erythrocytes

Pulmonary complications occur in a significant percentage of adults and children during the course of severe malaria. The cellular and molecular innate immune mechanisms that limit the extent of pulmonary inflammation and preserve lung function during severe Plasmodium infections remain unclear. In particular, the contributions to pulmonary complications by parasitized erythrocyte sequestration and subsequent clearance from the lung microvasculature by immune cells have not been clearly defined. We used the Plasmodium berghei ANKA‐C57BL/6 mouse model of severe malaria to investigate the mechanisms governing the nature and extent of malaria‐associated lung injury. We have demonstrated that sequestration of infected erythrocytes on postcapillary endothelial surfaces results in acute lung injury and the rapid recruitment of CCR2+CD11b+Ly6Chi monocytes from the circulation. These recruited cells remain in the lungs as monocyte‐derived macrophages and are instrumental in the phagocytic clearance of adherent Plasmodium berghei‐infected erythrocytes. In contrast, alveolar macrophages do not play a significant role in the clearance of malaria‐infected cells. Furthermore, the results obtained from Ccr2−/−, Cd36−/−, and CD36 bone marrow chimeric mice showed that sequestration in the absence of CD36‐mediated phagocytic clearance by monocytes leads to exaggerated lung pathologic features. In summary, our data indicate that the intensity of malaria‐induced lung pathologic features is proportional to the steady‐state levels of Plasmodium‐infected erythrocytes adhering to the pulmonary vasculature. Moreover, the present work has defined a major role of recruited monocytes in clearing infected erythrocytes from the pulmonary interstitium, thus minimizing lung damage.

Experimental Progressive Emphysema in BALB/cJ Mice as a Model for Chronic Alveolar Destruction In Humans.

Emphysema, one of the major components of chronic obstructive pulmonary disease (COPD), is characterized by the progressive and irreversible loss of alveolar lung tissue. Even though >80% of COPD cases are associated with cigarette smoking, only a relatively small proportion of smokers develop emphysema, suggesting a potential role for genetic factors in determining individual susceptibility to emphysema. Although strain-dependent effects have been shown in animal models of emphysema, the molecular basis underlying this intrinsic susceptibility is not fully understood. In this present study, we investigated emphysema development using the elastase-induced experimental emphysema model in two commonly used mouse strains, C57BL/6J and BALB/cJ. The results demonstrate that mice with different genetic backgrounds show disparate susceptibility to the development of emphysema. BALB/cJ mice were found to be much more sensitive than C57BL/6J to elastase injury in both a dose-dependent and time-dependent manner, as measured by significantly higher mortality, greater body weight loss, greater decline in lung function, and a greater loss of alveolar tissue. The more susceptible BALB/cJ strain also showed the persistence of inflammatory cells in the lung, especially macrophages and lymphocytes. A comparative gene expression analysis following elastase-induced injury showed BALB/cJ mice had elevated levels of il17A mRNA and a number of classically (M1) and alternatively (M2) activated macrophage genes, whereas the C57BL/6J mice demonstrated augmented levels of interferon-γ. These findings suggest a possible role for these cellular and molecular mediators in modulating the severity of emphysema and highlight the possibility that they might contribute to the heterogeneity observed in clinical emphysema outcomes.

Immune-mediated inflammation in the pathogenesis of emphysema: insights from mouse models

The cellular mechanisms that result in the initiation and progression of emphysema are clearly complex. A growing body of human data combined with discoveries from mouse models utilizing cigarette smoke exposure or protease administration have improved our understanding of emphysema development by implicating specific cell types that may be important for the pathophysiology of chronic obstructive pulmonary disease. The most important aspects of emphysematous damage appear to be oxidative or protease stress and sustained macrophage activation and infiltration of other immune cells leading to epithelial damage and cell death. Despite the identification of these associated processes and cell types in many experimental studies, the reasons why cigarette smoke and other pollutants result in unremitting damage instead of injury resolution are still uncertain. We propose an important role for macrophages in the sequence of events that lead and maintain this chronic tissue pathologic process in emphysema. This model involves chronic activation of macrophage subtypes that precludes proper healing of the lung. Further elucidation of the cross-talk between epithelial cells that release damage-associated signals and the cellular immune effectors that respond to these cues is a critical step in the development of novel therapeutics that can restore proper lung structure and function to those afflicted with emphysema.

Elastase-coupled beads as a tool for characterizing localized alveolar tissue destruction associated with the onset of emphysema

Intratracheal elastase challenge of laboratory animals has long been established as a model for observing the physiological and morphological changes that result from alveolar destruction, the hallmark of emphysema. However, instillation of elastase suspended in buffer results in widespread inflammation and variable emphysematous lesions, which has made the identification of specific cellular and molecular events associated with the onset of emphysema difficult to define. Here we establish a bead-based elastase delivery system that induces localized tissue destruction, a key event in the initiation of emphysema. Elastase was coupled to bisacrylamide beads, which were shown to retain enzymatic activity prior to intratracheal administration in mice. C57BL/6 mice were given a single dose of 40,000 beads, which became distributed throughout the small airways and parenchyma of the lung. Elastase-coupled beads resulted in a quantifiable loss of alveolar tissue immediately surrounding the beads, an effect that was not observed with beads that lacked protein altogether or with beads containing elastase inactivated by an irreversible inhibitor. Furthermore, beads bound with active elastase elicited local recruitment of mononuclear cells, including macrophages, and polymorphonuclear neutrophils to the site of bead deposition, a feature consistent with the cellular infiltration observed following conventional solubilized elastase challenges. This work identifies a novel bead-based enzyme delivery system that also extends the elastase model of emphysema to permit the characterization of mechanisms that drive alveolar surface area loss following elastin degradation in focal emphysematous lesions.