Macrophage Depletion Disrupts Immune Balance and Energy Homeostasis

Increased macrophage infiltration in tissues including white adipose tissue and skeletal muscle has been recognized as a pro-inflammatory factor that impairs insulin sensitivity in obesity. However, the relationship between tissue macrophages and energy metabolism under non-obese physiological conditions is not clear. To study a homeostatic role of macrophages in energy homeostasis, we depleted tissue macrophages in adult mice through conditional expression of diphtheria toxin (DT) receptor and DT-induced apoptosis. Macrophage depletion robustly reduced body fat mass due to reduced energy intake. These phenotypes were reversed after macrophage recovery. As a potential mechanism, severe hypothalamic and systemic inflammation was induced by neutrophil (NE) infiltration in the absence of macrophages. In addition, macrophage depletion dramatically increased circulating granulocyte colony-stimulating factor (G-CSF) which is indispensable for NE production and tissue infiltration. Our in vitro study further revealed that macrophages directly suppress G-CSF gene expression. Therefore, our study indicates that macrophages may play a critical role in integrating immune balance and energy homeostasis under physiological conditions

Air pollution and asthma — a review

In the last 15 years, asthma has become more prevalent, and now affects 1 in 7 children in Britain (Lee and Manning, 1995). Air pollution has also been associated with changes in mortality and hospital admissions in the US, the UK and in other countries world-wide. Adverse respiratory effects related to exposure to air pollutants have been documented and this paper highlights the influence of air pollution on the increased prevalence of asthma in Britain. For this paper the health effects of air pollutants have been investigated by reviewing the literature, which is based on two main methodologies: panel studies (sensitive patients studied with daily symptoms); and event studies (population effects studied during air pollution events). Panel studies have mainly been performed in the USA and Canada. These studies have generally concentrated upon children with asthma. There are fewer event studies but they are more international (Anderson et al, 1995; Stieb et al, 1996; Wordley, et al, 1997). Panel studies have shown modest daily variation in symptoms and lung function which are more marked in children with asthma than non-asthmatic children (Advisory Group on the Medical Aspects of Air Pollution Episodes (AGMAAPE), 1992, 1993, 1995). Mainly, the event studies have identified small effects in lung function in susceptible patients during air pollution episodes. Air pollutants are associated with decreased lung function, wheezing and other asthma symptoms more significant in children with asthma than non-asthmatic children. Although air pollution is not thought to be causal, evidence indicates that it may aid in sensitising individuals and aggravate asthma