Purpose: To investigate the extent and distribution of lymphangiogenesis in the rejected corneal graft, we determined the expression of several lymphangiogenic markers in rejected human corneal buttons.
Material and methods: Thirty-four corneal buttons were obtained from patients who underwent re-keratoplasty for graft rejection after penetrating keratoplasty. All corneas showed signs of rejection, such as, sudden mutton-fat keratic precipitates (KPs) or lines before re-keratoplasty. The corneas were halved, and one half was used for immunostaining and the other half was used for RT-PCR. Expression of vascular endothelial growth factor (VEGF)-A, VEGF-C, VEGF-D, VEGFR-2, VEGFR-3, LYVE-1 and podoplanin were measured as lymphangiogenic markers. Four non-operated normal corneas were used as controls.
Results: Numerous podoplanin positive cells were found in the anterior and posterior stroma. However, LYVE-1 positive mature lymphatics were found only in herpetic keratitis (HK)-induced graft rejection, and not in pseudophakic bullous keratopathy (PBK). RT-PCR showed that levels of VEGF-A, VEGF-C, VEGFR-2, and VEGFR-3 mRNAs were elevated in rejected corneal buttons versus the non-operated control corneas. Based upon the pre-keratoplasty pathologic conditions, HK cases showed higher levels of VEGF-A and VEGFR-2 than PBK. The mRNA ratios (keratoplastic cornea/normal cornea) for VEGF-A and VEGFR-2 were 8.9 and 5.8, respectively.
Conclusions: The results suggested that the VEGF-A and the VEGFR-2 may be a more important pathway for lymphangiogenesis in rejected corneal grafts than the VEGFR-3. In addition, organized lymphangiogenesis is more prominent in HK than PBK.
Keywords: Lymphangiogenesis; VEGF; VEGFR; penetrating keratoplasty; rejection.