Active in vitro reduction of antigen presenting cells in human corneal grafts using different chemokines.

Background: For the fate of a graft the antigen presenting cells play an important role. Chemokines can lead to enhanced migration of these cells. We therefore investigated if fresh human corneas bear the chemokine receptor 7 (CCR7) and if its ligands can force the emigration of dendritic cells in an in vitro model.
Methods: We used human corneas excluded for transplantation and performed migration tests using chemokine ligands 19 (CCL19) and 21 (CCL21) or the complement factor 5a (C5a). Emigrated cells were collected up to 35 days and stained by immunofluorescent double labeling in triple layer technique with Langerin/CD207, DC-SIGN/CD209, CD14, and HLA-DR. In parallel, fresh and cultured human corneas were stained for CCR7.
Results: We found in fresh human corneas, as well as in long-term cultured ones, a low CCR7 expression that nearly diminished after 28 days. In vitro Langerhans cell emigration could be enhanced only by CCL19, whereas dendritic cells were strongly influenced by CCL19, CCL21, and C5a. HLA-DR(+) cells showed numerically the highest in vitro emigration rate. Macrophages/monocytes were not influenced by the used chemokines.
Conclusions: Although human corneas reduce their antigen presenting cells numbers during long-term culture, this effect could be significantly enhanced by using chemokines.