Targeted surface marker screening on neuronal structures in the human choroid

While choroidal neuronal control is known to be essential for retinal and ocular health, its mechanisms are not understood. Especially, the local choroidal innervation mediated by intrinsic choroidal neurons (ICN) remains enigmatic. Neuronal functionality depends on the synaptic neurotransmitters and neuroregulatory peptides involved as well as from membrane components presented on the cell surface. Since the neuronal surface molecular expression patterns in the choroid are currently unknown, we sought to determine the presence of various cluster-of-differentiation (CD) antigens in choroidal neuronal structures with a particular focus on ICN. Human choroids were prepared for immunohistochemistry and the pan-neuronal marker PGP9.5 was combined with CD15, CD24, CD29, CD34, CD46, CD49b, CD49e, CD56, CD58, CD59, CD71, CD81, CD90, CD146, CD147, CD151, CD165, CD171, CD184, CD200, CD271 and fluorescence- and confocal laser scanning-microscopy was used for documentation. The following antigens were found to be co-localized in PGP.9.5+ nerve fibers and ICN perikarya: CD29, CD34, CD56, CD81, CD90, CD146, CD147, CD151, CD171, CD200 and CD271, while all other CD markers where not detectable. Whereas CD24^- and CD59^- immunoreactivity was clearly absent in ICN perikarya, some neural processes of the choroidal stroma displayed CD24 and CD59 immunopositivity. While a multitude of the aforementioned CD-markers were indeed detected in nervous structures of the choroid, the CD24⁺ and CD59⁺ nerve fibers most likely have extrinsic origin from cranial ganglia since ICN cell bodies were found to lack both markers. These findings illustrate how the detailed analysis of CD molecules described here opens novel avenues for future functional studies on choroidal innervation and its control.