The presence of antigen-presenting cells and hem- and lymphangiogenesis in the cornea are risk factors for the rejection of corneal transplants. We previously reported that antigen-presenting cells such as macrophages (MPs) play an important role in the induction of lymphatic endothelial cells during inflammation. This prompted us to inquire whether the existence of lymphatic vessels in the cornea is associated with the activation of MPs during inflammation.
To investigate this question, we performed suture placement on the cornea to induce inflammation. We found that a large number of MPs were recruited and that lymphatic vessels were formed in response. Next, as C57BL/6 mice have a higher rejection rate after corneal transplantation than BALB/c mice, we compared the corneas of C57BL/6 and BALB/c mice under normal and inflamed conditions. We found that the number of spontaneously formed lymphatic vessels in the C57BL/6 corneas was significantly greater than in the BALB/c corneas, and that there were more activated MPs in the C57BL/6 corneas than in the BALB/c corneas. Additionally, to confirm that activated MPs induced and maintained lymphatic vessels in the cornea, we depleted the number of MPs in C57BL/6 mice via clodronate liposomes. We found that MP depletion reduced the spontaneous formation of lymphatic vessels and reduced inflammation-induced lymphangiogenesis relative to control mice. Finally, we found that mice deficient in MP markers had fewer spontaneously formed lymphatic vessels and less lymphangiogenesis than control C57BL/6 mice. The evidence gathered in this study leads us to conclude that activated MPs appear to play an important role in the formation of new lymphatic vessels and in their maintenance.
Nippon Ganka Gakkai Zasshi (J Jpn Ophthalmol Soc) 118: 953-957, 2014.