Extracellular matrix components in a case of retrocorneal membrane associated with syphilitic interstitial keratitis

Purpose. A web-like retrocorneal membrane (RCM) is an uncommon complication of chronic syphilitic interstitial keratitis. Extracellular matrix compone nts have not yet been defined in this structure, although previous histolog ic examinations have suggested the presence of collagen. We examined the pr esence and distribution of extracellular matrix components in a patient wit h an RCM. Methods. A specimen of the opaque cornea affected by syphilitic i nterstitial keratitis with RCM formation was obtained during penetrating ke ratoplasty in a 62-year-old woman and was evaluated by histology, immunohis tochemistry, and scanning electron microscopy (SEM). Antibodies against col lagen types I, III, and IV; fibronectin; vimentin; alpha -smooth muscle act in (alpha -SMA); heat shock protein 47 (Hsp 47); proliferating cell nuclear antigen (PCNA); and Ki67 were used. Results. Histologic analysis detected multiple concentric, acellular layers positive for collagen types I, III, a nd IV. The corneal endothelial cells (CECs) were positive for vimentin, col lagen I, fibronectin, and Hsp 47 but not for alpha -SMA. Furthermore, the C ECs were negative for PCNA and Ki67, indicating that they were not prolifer ating. SEM revealed the RCM was covered by CECs with a fibroblastic appeara nce. Conclusion, RCM associated with syphilitic interstitial keratitis cont ained collagen types I, III, and IV and fibroblast-like CECs. These CECs ma y secrete the extracellular matrix components found in the RCM. Hsp 47 up-r egulation in the CECs may play an important role in RCM formation. These fi ndings provide further insights into the phenotypic modulation of CECs.