Changes in Macrophages in Pulmonary Hypertension: A Focus on High-altitude Pulmonary Hypertension

High-altitude pulmonary hypertension (HAPH) is a condition characterized by elevated pulmonary arterial pressure exceeding normal physiological values, resulting from a combination of high-altitude low-pressure, hypoxic environments, genetic susceptibility, immune dysfunction, and neurogenic disturbances. This condition predominantly manifests as right heart failure, severely impacting quality of life and life expectancy. Macrophages, as one of the most prevalent innate immune cells, have been increasingly recognized for their crucial role in the pathogenesis of HAPH. The low-pressure and hypoxic environment, along with other etiological factors, lead to metabolic abnormalities in tissue cells and the microenvironment. This results in increased secretion of chemokines, cytokines, and growth factors in the microenvironment, which promote the proliferation of tissue-resident macrophages and the differentiation of monocytes recruited from the blood into macrophages. This exacerbates the inflammatory cascade, further promoting cell proliferation, tissue repair, and inhibition of apoptosis. These processes contribute to the migration and proliferation of pulmonary arterial smooth muscle cells, endothelial cells, and fibroblasts, leading to vascular remodeling and ultimately the development of pulmonary arterial hypertension. This review examines the role of macrophage-mediated immune responses in high-altitude pulmonary arterial hypertension, with a focus on hypoxia as a key feature.