Figure 4. The role of macrophages in viral myocarditis.

In homeostasis, two ontologically different populations of macrophages (MΦ), with different functions, reside in the heart. Upon viral infection, the resident cells of the myocardium produce chemokines that promote the recruitment of monocytes, which in turn differentiate into macrophages with proinflammatory functions. However, besides the fact that their numbers recede, little is known about the role of resident macrophages during and after infection, and many questions remain (see boxes). The difficulty in distinguishing these different populations using (significantly overlapping) surface markers adds to the challenges faced in addressing these questions.