The HNK-1 epitope and the elastic fiber system of the human ciliary body. An immunoelectron microscopic study.

PURPOSE To localize at the electron microscopic level the cell adhesion-related HNK-1 carbohydrate epitope in the inner connective tissue layer (ICTL) of the human ciliary body. METHODS Seven specimens representing the pars plicata (age range, 12 to 86 years) and three specimens representing the pars plana (age range, 29 to 71 years) of the ciliary body were sampled at death from eight normal human eyes. Three additional specimens from the pars plicata were taken from three eyes with exfoliation syndrome (age range, 78 to 81 years). All specimens were embedded in LR white resin and studied by postembedding immunogold labeling using two monoclonal antibodies (mAbs) HNK-1 and NC-1 in detecting the HNK-1 epitope. RESULTS In the ICTL of the pars plicata and the pars plana, mAbs HNK-1 and NC-1 constantly bound to the surface of fibroblast-like cells present in the subepithelial connective tissue matrix. The immunoreaction was localized along the cell membrane, both around the cell body and around its long, slender cytoplasmic processes. Long microfibrillar bundles, which consisted of approximately 10-nm thick microfibrils in close association with these subepithelial matrix cells and elastic fibers, were also labeled. The periphery of elastic fibers was likewise immunolabeled for the HNK-1 epitope. The reaction pattern was essentially the same, regardless of age and presence or absence of exfoliation syndrome. CONCLUSIONS At the ultrastructural level, the HNK-1 epitope in the ICTL is a common denominator to the subepithelial matrix cells, microfibrillar bundles, and elastic fibers. This suggests that the subepithelial matrix cells secrete this epitope, and that molecules hearing it may be involved in joining these connective tissue elements that structurally stabilize the ciliary body.