Change in Performance of BALB/c Mouse Pulmonary Macrophage Surface Receptor after Exercise and its Influence on Phagocytic Activity

Objective: To study the effect of exercise on phagocytosis by pulmonary bronchoalveolar macrophages (BAMs). Methods: A total of 120 seven- to nine-week-old male BALB/c mice were randomly assigned into the following groups based on exercise intensity on a treadmill: control exercise (CE) group, acute moderate exercise (ME) group, and strenuous exercise group. Lung lavage was conducted to collect BAMs from the mice. Phagocytic behavior and surface receptor expression on BALB/c mouse BAMs were analyzed through fluorescence microscopy and flow cytometry. Results: In the SE group, expression levels of macrophage scavenger receptors (surface receptor [SR-A] type I/II and macrophage receptor [MARCO], complement receptor3 (CR3), and intercellular adhesion molecule 1 (ICAM-1) were upregulated; by contrast, expression level of extensive G-type immune globulin receptor (Fc Rs) was not upregulated. The promoting percentage of phagocytosis in the CE group was 100%; the highest promoting percentage of phagocytosis was 161% observed in MARCO, followed by 116% detected in CR3; the promoting percentage of phagocytosis found in SR-A type I/II and ICAM-1 increased by approximately 65%. Indeed, these scavenger receptors were involved in phagocytosis induced by macrophages. MARCO was also necessary to elicit a stimulatory effect on macrophage phagocytic activity. Conclusions: The phagocytosis of unopsonized particles was possibly mediated by MARCO expression.