Heterogeneity of collagens in rabbit cornea: type III collagen.

Whole neonate rabbit corneas and adult corneas containing 2-week-old scars were incubated in the presence of [ I4 C] glycine. Radiolabeled collagen extracted from the corneas and scar tissue were analyzed by sodium dodecylsulfate/polyacrylamide gel electrophoresis and fluorography to determine the types and relative quantity of collagen polypeptides present and synthesized by these tissues. In addition to other collagen types, type III was found in both neonate cornea and scar tissue from adult cornea, albeit in relatively small quantities. Type III collagen in normal cornea was associated with the residue after pepsin digestion and formic acid extraction of the tissue, and the same type of collagen was extracted from scar tissue after similar treatment. Type III collagen-specific monoclonal antibody bound to developing normal corneas and healing adult tissue sections, as determined by immunofluorescence. Antibody binding was localized to the endothelium and growing Descemet's membrane in fetal and neonate corneas, and restricted to the most posterior region of the corneal scar tissue. Although monoclonal antibody to keratan sulfate, used as a marker for stromal fibroblasts, bound to most of the scar tissue, the antibody failed to bind to the posterior scar tissue positive for type III collagen. We conclude that endothelial cells from fetal and neonate rabbit cornea and endothelium-derived fibroblasts from healing wounds of adult cornea synthesize and deposit type III collagen. Moreover, this collagen appears to be incorporated into the growing Descemet's membrane of normal corneas and narrow posterior portion of the scar tissue. Although type III collagen remains associated with normal adult Descemet's membrane, subsequent disappearance of type III collagen-specific fluorescence in healing wounds may result from breakdown or masking of this collagen during scar remodelling. Invest Ophthalmol Vis Sci 29:767-775, 1988 Numerous immunohistochemical and biochemical studies have been conducted to determine the presence and location of type III collagen in corneal tissues. The apparently conflicting results may be a result of different techniques, animal species or tissue sources. For example, biochemical analyses of bovine corneas have shown the presence of type III collagen. Some studies claimed that type III collagen is found in calf as well as adult bovine corneas and constitutes up to 20% of the total collagen in the tissue. 1 ' 2 Others reported type III collagen in fetal bovine corneas as a minor component but not detectable in adult tissue. 3 ' 4 Type III collagen was also found in adult