The atypical chemokine receptor-2 does not alter corneal graft survival but regulates early stage of corneal graft-induced lymphangiogenesis

PURPOSE: To re-evaluate the role of the atypical chemokine receptor-2 (ACKR2) in corneal graft rejection and investigate the effect of ACKR2 on inflammation-associated lymphangiogenesis using murine orthotopic corneal transplantation. METHODS: Corneal grafts were performed and evaluated in the settings of syngeneic, allogeneic and single antigen (HY-antigen) disparity pairings. Corneal vessels were quantified in whole mounts from WT, ACKR2(−/−) and F4/80(−/−)ACKR2(−/−) mice that received syngeneic or allogeneic grafts using anti-CD31 and anti-Lyve-1 antibodies. RESULTS: Syngeneic corneal grafts in WT and ACKR2(−/−) mice were 100% accepted. Fully histo-incompatible allogeneic grafts were rapidly rejected (100%) with similar tempo in both WT and ACKR2(−/−) hosts. Around 50% of single-antigen (HY) disparity grafts rejected at a slow but similar tempo (60 days) in WT and ACKR2(−/−) mice. Prior to grafting, F4/80(−/−)ACKR2(−/−) mice had lower baseline levels of limbal blood and lymphatic vessels compared to ACKR2(−/−) mice. Syngeneic grafts, but not allogeneic grafts, in ACKR2(−/−) and F4/80(−/−)ACKR2(−/−) mice induced higher levels of lymphatic sprouting and infiltration of Lyve-1(+) cells during the early (3d) post-graft (pg) stage but lymphatic density was similar to WT grafted mice by 7d pg. CONCLUSIONS: Our results indicate that the chemokine scavenger receptor, ACKR2, has no role to play in the survival of allogeneic grafts. A minor role in regulation of lymphangiogenesis in the early stage of wound healing in syngeneic grafts is suggested, but this effect is probably masked by the more pronounced lymphangiogenic inflammatory response in allogeneic grafts. No additional effect was observed with the deletion of the resident macrophage gene, F4/80.