In the inflamed cornea, there is a parallel outgrowth of blood and lymphatic vessels into the normally avascular cornea. We tested whether adaptive and/or innate immune cells were actively involved in the genesis of new lymphatic vessels. Our results indicate that innate immune cells (CD11b + macrophages, but not CD11c + dendritic cells) physically contributed to lymphangiogenesis under pathological conditions and that bone marrow-derived CD11b + macrophages expressed lymphatic endothelial markers such as LYVE-1 and Prox-1 under inflamed conditions in the corneal stromata of mice. Furthermore, blood vascular endothelial cells that expressed the Tie2 promoter did not contribute to newly formed lymphatic vessels under inflamed conditions. Our in vitro experiments demonstrated that CD11b + macrophages alone were capable of forming tube-like structures that expressed markers of lymphatic endothelium such as LYVE-1 and podoplanin. The novel finding that CD11b + macrophages are critical for the development of inflammation-dependent lymphangiogenesis in the eye suggests a new mechanism of lymphangiogenesis.

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Impaired wound healing is a common complication of diabetes. Although it is well known that both macrophages and blood vessels are critical to wound repair, the role of wound-associated lymphatic vessels has not been well investigated. We report that both the presence of activated macrophages and the formation of lymphatic vessels are rate-limiting to the healing of diabetic wounds. We have previously shown that macrophages contribute to the lymphatic vessels that form during the acute phase of corneal wound healing. We now demonstrate that this is a general phenomenon; cells that co-stain for the macrophage marker F4/80 and the lymphatic markers LYVE-1 (lymphatic vascular endothelium hyaluronate receptor) and podoplanin contribute to lymphatic vessels in full-thickness wounds. LYVE-1-positive lymphatic vessels and CD31-positive blood vessels were significantly reduced in corneal wound healing in diabetic mice (db/db) (P < 0.02) compared with control (db/؉) mice. Glucose treatment of control macrophages led to the down-regulation of the lymphaticspecific receptor VEGFR3 and its ligands, vascular endothelial growth factor-C and -D (VEGF-C, -D). Interleukin-1␤ stimulation rescued diabetic macrophage function; application of interleukin-1␤-treated db/db-derived macrophages to wounds in db/db mice induced lymphatic vessel formation and accelerated wound healing. These observations suggest a potential therapeutic approach for healing wounds in diabetic patients.