Within turbulent regions of the heart, the spindly fingers of dendritic cells (DCs) probe pumping blood in search of antigens, Choi and colleagues demonstrate on page 497. Known for their role in both warding off and tolerating infection, these potent antigen presenters bring a new dimension to cardiovascular inflammation.

Choi et al. spotted DCs congregating at the base of the aorta and around cardiac valves in healthy, CD11c-EYFP transgenic mice. The cells nestled beneath the epithelium of the innermost vessel layers with some of their slim dendritic processes dangling into the lumen where they captured circulating molecules—much like DC processes in the intestines, lungs, and other organs do.

In independent studies with two model antigens (ovalbumin and a malaria protein), the authors showed that these cells not only looked like DCs but acted like them too. Aortic DCs cross-presented injected and blood-borne antigens to CD8+ T cells.

Compared with their contemporaries in the spleen, DCs of the aorta and heart valves expressed lower levels of costimulatory molecules, indicating that they may be resting in healthy mice. However, aortic cells expressing CD11c have been shown to increase during aging and atherosclerosis. Thus Choi et al. speculate that aortic DCs may lead to problems if triggered by insult or infection. Now that these researchers have determined that DCs are indeed there, they can begin to study their role in heart disease.