Mechanisms and Effects of Macrophage Polarization and Its Specifics in Pulmonary Environment

Macrophages are a specific group of cells found in all body tissues. They have specific characteristics in each of the tissues that correspond to the functional needs of the specific environment. These cells are involved in a wide range of processes, both pro-inflammatory and anti-inflammatory ("wound healing"). This is due to their specific capacity for so-called polarization, a phenotypic change that is, moreover, partially reversible compared to other differentiated cells of the human body. This promises a wide range of possibilities for its influence and thus therapeutic use. In this article, we therefore review the mechanisms that cause polarization, the basic classification of polarized macrophages, their characteristic markers and the effects that accompany these phenotypic changes. Since the study of pulmonary (and among them mainly alveolar) macrophages is currently the focus of scientific interest of many researchers and these macrophages are found in very specific environments, given mainly by the extremely high partial pressure of oxygen compared to other locations, which specifically affects their behavior, we will focus our review on this group.

Intonation of Nrf2 and Hif1-α pathway by curcumin prophylaxis: A potential strategy to augment survival signaling under hypoxia

BACKGROUND

Pulmonary surfactant oxidation leads to alveolar collapse- a condition often noticed in high altitude pulmonary edema (HAPE). The present study was aimed to determine the effect of curcumin prophylaxis in augmenting the phase II antioxidant enzymes and surfactant proteins expression in enabling the pulmonary surfactant homeostasis under hypoxia.

METHODS

A549 cells were exposed to 3% hypoxia for different time durations (1 h, 3 h, 6 h, 12 h and 24 h). The Cells were pretreated (1 h) with 10 μM curcumin and exposed to hypoxia. The in-vivo results were extrapolated into in-vivo system using male Sprague Dawley rats, exposed to a stimulated altitude of 7620 m for 6 h. The rats were supplemented with curcumin (50 mg/kgBW) 1 h prior to hypoxia exposure.

RESULTS

Results showed that, the expression of surfactant proteins (SPs) A and B decreased from 3 h of hypoxic exposure, whereas expression of SP-C and SP-D proteins were increased within 1 h of hypoxic exposure over control cells. Hypoxic exposure resulted into significant increase in protein and lipid peroxidation (p < 0.001), reduced levels of antioxidants (GSH, GPx and SOD) (p < 0.001) along with significant down regulation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and Heme oxygenase-1 (HO-1) in A549 cells over control. However, the curcumin supplementation both in-vitro and in-vivo resulted into increased expressions of HO-1 and Nrf2 significantly (p < 0.001), which enabled the cells in balanced expression of SPs with reduced levels of oxidants. Further curcumin significantly enhanced the levels of antioxidant enzymes in BALF along with stabilized expression of hypoxia inducible factor 1(HIF-1α) followed by reduced expression of vascular endothelial growth factor (VEGF) in lungs of rats. The immunohistochemistry observations provided substantial evidence of enhanced surfactant protein expressions in lungs of curcumin administered hypoxia exposed rats.

CONCLUSION

These results indicate that curcumin augment survival signaling by reinforcing the induction of phase II antioxidant enzymes thereby enabling the pulmonary surfactant homeostasis under hypoxia.

Evolution, Development, and Function of the Pulmonary Surfactant System in Normal and Perturbed Environments

Surfactant lipids and proteins form a surface active film at the air-liquid interface of internal gas exchange organs, including swim bladders and lungs. The system is uniquely positioned to meet both the physical challenges associated with a dynamically changing internal air-liquid interface, and the environmental challenges associated with the foreign pathogens and particles to which the internal surface is exposed. Lungs range from simple, transparent, bag-like units to complex, multilobed, compartmentalized structures. Despite this anatomical variability, the surfactant system is remarkably conserved. Here, we discuss the evolutionary origin of the surfactant system, which likely predates lungs. We describe the evolution of surfactant structure and function in invertebrates and vertebrates. We focus on changes in lipid and protein composition and surfactant function from its antiadhesive and innate immune to its alveolar stability and structural integrity functions. We discuss the biochemical, hormonal, autonomic, and mechanical factors that regulate normal surfactant secretion in mature animals. We present an analysis of the ontogeny of surfactant development among the vertebrates and the contribution of different regulatory mechanisms that control this development. We also discuss environmental (oxygen), hormonal and biochemical (glucocorticoids and glucose) and pollutant (maternal smoking, alcohol, and common "recreational" drugs) effects that impact surfactant development. On the adult surfactant system, we focus on environmental variables including temperature, pressure, and hypoxia that have shaped its evolution and we discuss the resultant biochemical, biophysical, and cellular adaptations. Finally, we discuss the effect of major modern gaseous and particulate pollutants on the lung and surfactant system.

Characterizing Pneumocystis in the lungs of bats: understanding Pneumocystis evolution and the spread of Pneumocystis organisms in mammal populations

Bats belong to a wide variety of species and occupy diversified habitats, from cities to the countryside. Their different diets (i.e., nectarivore, frugivore, insectivore, hematophage) lead Chiroptera to colonize a range of ecological niches. These flying mammals exert an undisputable impact on both ecosystems and circulation of pathogens that they harbor. Pneumocystis species are recognized as major opportunistic fungal pathogens which cause life-threatening pneumonia in severely immunocompromised or weakened mammals. Pneumocystis consists of a heterogeneous group of highly adapted host-specific fungal parasites that colonize a wide range of mammalian hosts. In the present study, 216 lungs of 19 bat species, sampled from diverse biotopes in the New and Old Worlds, were examined. Each bat species may be harboring a specific Pneumocystis species. We report 32.9% of Pneumocystis carriage in wild bats (41.9% in Microchiroptera). Ecological and behavioral factors (elevation, crowding, migration) seemed to influence the Pneumocystis carriage. This study suggests that Pneumocystis-host association may yield much information on Pneumocystis transmission, phylogeny, and biology in mammals. Moreover, the link between genetic variability of Pneumocystis isolated from populations of the same bat species and their geographic area could be exploited in terms of phylogeography.

Effects of surfactant protein-A on the interaction of Pneumocystis murina with its host at different stages of the infection in mice

We examined the effects of surfactant protein A (SP-A), a collectin, on the interaction of Pneumocystis murina with its host at the beginning, early to middle, and late stages of infection. Pneumocystis murina from SP-A wild-type (WT) mice inoculated intractracheally into WT mice (WT(S)-WT(R)) adhered well to alveolar macrophages, whereas organisms from SP-A knockout (KO) mice inoculated into KO mice (KO(S)-KO(R)) did not. Substitution of WT mice as the source of organisms (WT(S)-KO(R)) or recipient host macrophages (KO(S)-WT(R)) restored adherence to that found with WT(S)-WT(R) mice. In contrast, when immunosuppressed KO and WT mice were inoculated with P. murina from a homologous source (KO(S)-KO(R), WT(S)-WT(R)) or heterologous source (WT(S)-KO(R), KO(S)-WT(R)) and followed sequentially, WT(S)-KO(R) mice had the highest levels of infection at weeks 3 and 4; these mice also had the highest levels of the chemokine macrophage inflammatory protein-2 and neutrophils in lavage fluid at week 3. Surfactant protein-A administered to immunosuppressed KO(S)-KO(R) mice with Pneumocystis pneumonia for 8 wk as a therapeutic agent failed to lower the organism burden. We conclude that SP-A can correct the host immune defect in the beginning of P. murina infection, but not in the middle or late stages of the infection.