Expression of podoplanin and other lymphatic markers in the human anterior eye segment

To investigate the expression of lymphatic endothelial cell (LEC) markers in tissues of the anterior eye segment.

Sections of human anterior segments from eight eyes of eight donors (37-100 years) were stained for Vegf-R3, Prox-1, Lyve-1, Pdpn, Pcx, CCR7, Ccl19, Ccl21, and CD68. Pdpn localization was additionally analyzed by immunogold labeling on sections of five eyes. Expression of LEC markers and chemokine receptor/ligands was analyzed by RT-PCR in iris and trabecular meshwork (TM) tissue from three eyes and eight human TM (hTM) cell cultures.

Vegf-R3 and Prox-1 stained no structures in the anterior segment. Lyve-1 stained single dendriform cells in the ciliary body, the TM, and the iris. Pdpn stained all trabecular cells, the cells of the trabeculum ciliare, and the anteriormost perimysium cells of the ciliary muscle. Schlemm's canal endothelium was not stained but reacted to a podocalyxin antibody. In the iris stroma, single dendriform cells were stained; at the anterior surface, almost all cells were Pdpn(+). Few stromal cells were Pdpn(+)/Lyve(+), but several anterior surface cells were Pdpn(+)/Ccl21(+). Solitary CCR7(+) cells were observed there, too. IF results were confirmed by PCR, but Prox-1 was detected in TM and iris. Cultured hTM cells displayed partial Pdpn/Ccl21 colocalization.

Coexpression of Pdpn and Ccl21 at the anterior iris surface and in the chamber angle suggests the constitution of a chemokine gradient guiding APCs through the anterior chamber. The more pronounced expression of Pdpn in the TM could favor egression of APCs by way of the conventional outflow.