MRC1 and asthma: However, recent studies have revealed that asthma has also been found to be associated with an upregulation of M2 macrophages19,20, and M2 macrophages are known to express MRC1 on their surface and secrete FGF, Transforming growth factor- β (TGF-β), and MMP, which are highly associated with the airway remodeling seen in chronic asthma patients42–44.