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M.P. Watson, A.J. T. George, D.F. P. Larkin; Costimulatory Molecules on Murine Endothelium; Implications for Corneal Graft Rejection . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3591.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: T lymphocytes have a central role in allograft rejection, including cornea. On engagement of the T cell receptor by antigenic peptide–MHC complex, a second ‘costimulatory’ signal is critical to T cell activation or otherwise. Having already shown that blockade of CD28 and/or CD40 costimulatory molecules can prolong corneal transplant survival in vivo (IOVS 2003), an in vitro correlate of corneal allograft rejection has been established to characterise the expression of costimulatory molecules on murine corneal endothelium and their response to pro–inflammatory cytokines (TNFα, IL–1α, IFNγ). Methods: Initial characterisation was carried out on two murine endothelial cell lines, cornea (MCEC) and vascular (sEnd.1) followed by primary corneal endothelium cultured in vitro. Expression on unmodified and cytokine stimulated cells was determined by flow cytometry. T cell proliferation was measured by 3H–thymidine incorporation. Results: As cornea is an immune privileged tissue we first studied the presence of ligands that generate negative costimulatory signals. Neither PD–L1 nor PD–L2 was constitutively expressed on primary corneal cells or MCEC but PD–L1 was upregulated following cytokine stimulation. Similar expression was found on the sEnd.1. Of the positive costimulation ligands, CD40 expression was present on MCEC but not on primary corneal cells or sEnd.1 whereas ICOSL was absent on all cell types. CD80 and CD86 ligands can act as either positive or negative costimulation through CD28/CTLA4 respectively. There was constitutive expression of CD80 on primary corneal cells whereas CD86 was undetectable on all cell types. Primary corneal endothelium stimulated with cytokine prior to co–culture demonstrated T cell proliferation that was greater than unstimulated endothelium. Conclusions: We have shown that corneal endothelium not only expresses costimulatory molecules but also has the capacity to stimulate T cells. Expression of CD80 acting as a positive costimulatory signal through CD28 ligation may explain in part why corneal allografts undergo rejection despite relative immune privilege. However the presence of PD–L1 and CD80, when ligating PD–1 and CTLA4 respectively play a role in prolonging corneal allograft survival due to T cell inhibition. Expression on transplanted corneal endothelium may allow costimulation of recipient T cells in the anterior chamber in addition to the lymphatic system.
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