STROMAL FIBROBLASTS ARE ASSOCIATED WITH COLLAGEN-IV IN SCAR TISSUES OF ALKALI-BURNED AND LACERATED CORNEAS

Purpose. Corneal wound healing frequently leads to the formation of op aque scar tissue. We examined whether stromal fibroblastic cells of in jured corneas express collagen IV and contributes to the formation of a basal lamina-like structure. Methods. Rabbits were anesthetized, and central corneal alkali burn (8 mm in diameter; 1 M NaOH, 1 min) or la ceration (8 mm long) were produced. The injured corneas, which had hea led for 1, 7, 21 and 45 days, were subjected to histological and immun ohistochemical studies with goat anti-collagen IV antibodies, using li ght and electron microscopy, and in situ hybridization with an antisen se digoxigenin-labeled riboprobe of collagen alpha 1(IV) mRNA. For com parison, twenty-day-old fetal corneas were subjected to immunohistoche mical study and transmission electron microscopy (TEM). Results. TEM e xaminations revealed that the stromal collagenous matrix was organized in orthogonal lamellae during corneal development, whereas that of al kali-burned cornea, which had healed for 3 weeks, was disorganized. Th e stroma of twenty-day-old fetal cornea was not labeled by the anti-co llagen IV antibodies. In contrast, one week after injury, specific col lagen IV immunostaining was detected in the injured stroma. As the hea ling proceeded (21-45 days), the antibodies reacted with fibroblastic cells and the extracellular matrix of scar tissues located in the ante rior portion of alkali-burned corneas, as well as the posterior portio n of lacerated corneas. The middle portion of the stromal tissues was weakly labeled by the anti-collagen IV antibodies with the exception o f the blood vessel wall. Immune-electron microscopic study showed that collagen IV and fibronectin were closely associated with the fibrobla stic cells. In situ hybridization demonstrated that epithelial and end othelial cells and fibroblastic cells in the wounded corneal stroma an d retro-corneal membrane expressed alpha 1(IV) mRNA, whereas in normal corneas the expression of alpha 1(IV) mRNA was limited to epithelial and endothelial cells. Conclusions. The enhanced expression of collage n IV by the fibroblastic cells in the stroma of injured corneas is con sistent with the notion that they may contribute to the formation of b asal lamina-like structures in injured corneas.