What's eating you? An update on Giardia, the microbiome and the immune response

Giardia intestinalis has been observed in human stools since the invention of the microscope. However, it was not recognized as a pathogen until experimental infections in humans in the 1950s resulted in diarrheal illness [1]. We now know that this protozoan is capable of inducing a malabsorptive diarrhea and that the parasite is a major contributor to stunting in young children [2]. However, the majority of infections with this parasite are not accompanied by overt diarrhea and several studies indicate that it actually has a protective effect against moderate-severe diarrhea [3]. There is therefore significant interest in the mechanisms responsible for the wide variation observed in the clinical outcomes of infection with Giardia. This review will highlight recent work on the interactions among the parasite, the host microbiome and the immune response as contributing to this variation.

Adventitial remodeling after angioplasty is associated with expression of tenascin mRNA by adventitial myofibroblasts

OBJECTIVES

The purpose of this study was to determine the temporospatial expression of tenascin-C (TnC) in balloon-injured rat and porcine arteries.

BACKGROUND

Recent studies suggest that cell migration, in addition to cell proliferation, is a critical component of neointima formation after vascular injury. We have previously shown that adventitial myofibroblasts synthesize growth factors that contribute to the formation of neointima after arterial injury. We have also shown that the extracellular matrix protein, TnC, regulates cell migration. Consequently, we investigated the temporospatial expression of TnC by myofibroblasts after vascular injury.

METHODS

In situ hybridization and immunohistochemistry were used to investigate the temporospatial expression of TnC in injured arteries. Northern and Western blots were used to determine the in vitro expression of TnC.

RESULTS

In situ hybridization revealed that the major site of TnC expression early after vascular injury was the adventitial myofibroblasts. Immunohistochemical staining demonstrated that TnC expression began in adventitial myofibroblasts three days after injury. Tenascin-C expression, however, did not persist in this region. Rather, it moved progressively across the vascular wall toward the luminal surface. By one week, TnC expression reached the developing neointima. In vitro, myofibroblasts did not express TnC mRNA under basal conditions. In contrast, angiotensin II and PDGF-BB, factors that have been implicated in remodeling of balloon-injured arteries, markedly upregulated TnC mRNA.

CONCLUSIONS

Tenascin-C is expressed in response to balloon injury. Tenascin-C expression begins with adventitial myofibroblasts. Over a period of 7 to 14 days, expression moves progressively across the vessel wall to the neointima. We hypothesize that adventitial myofibroblasts are actively involved in the formation of neointima and that TnC facilitates migration of these cells during adventitial remodeling.

CC chemokine receptor 2 is required for macrophage infiltration and vascular hypertrophy in angiotensin II-induced hypertension

Recent studies have identified the presence of macrophages in the arterial wall of hypertensive animals and suggested that as is the case in atherosclerosis, macrophage products may be important mediators of the adaptive response of the arterial wall. In support of this, we have previously shown that the expression of monocyte chemoattractant protein-1 is upregulated in the arteries of hypertensive animals. We hypothesized that macrophage recruitment is a critical step in the pathogenesis of hypertension. To obtain insights into this potential mechanism, we made use of mice deficient in the CC chemokine receptor 2 (CCR2), the receptor for monocyte chemoattractant protein-1. Hypertension was induced with the subcutaneous administration of angiotensin II (0.75 mg. kg(-1). d(-1)) for 7 days. Using in situ hybridization with a probe for c-fms to identify macrophages, we found that hypertension-induced macrophage infiltration of the arterial wall was virtually eliminated in CCR2-deficient mice. In addition, vascular hypertrophy was reduced by approximately 65% compared with wild-type animals. These data demonstrate that CCR2 is essential for the recruitment of macrophages into the arterial wall in the setting of hypertension. Furthermore, the decreased hypertrophic response suggests that vascular hypertrophy occurs in part as a consequence of macrophage infiltration. In angiotensin II-induced hypertension, CCR2-mediated responses are critical to the process of macrophage recruitment and vascular hypertrophy and may represent one mechanism by which at least some forms of hypertension may lead to the development of atherosclerosis.