MOST ANCHORING FIBRILS IN HUMAN SKIN ORIGINATE AND TERMINATE IN THE LAMINA DENSA

Anchoring fibrils (AF) at the dermo-epidermal junction are well charac terized as ultrastructural entities. They are composed mainly of colla gen VII and play a key role in dermo-epidermal adhesion. Previous stud ies have suggested that AF originate in the lamina densa (LD), extend perpendicularly into the dermis, and insert into amorphous elements, c alled ''anchoring plaques,'' in the dermal connective tissue. To eluci date the precise structural organization of the AF network in human sk in, we analyzed quantitatively the distribution of different domains o f collagen VII in the epidermal basement membrane zone, using various techniques of immunoelectron microscopy with a range of domain-specifi c antibodies that we prepared. Some electron-dense amorphous structure s (ie, anchoring plaques) that were positive with aminoterminal end of collagen VII could be recognized only by pre-embedding en bloc labeli ng, and not by postembedding section labeling of immunoelectron micros copy. Quantitative analysis of surface labeling with postembedding imm unoelectron microscopy demonstrated that most (>90%) gold particles la beling the epitopes in the aminoterminal (NC-1 domain) of collagen VII were precisely localized to the LD, whereas no specific labeling was observed in the dermis. Most (>90%) of the gold particles labeling the carboxyterminal end of collagen VII localized at a 160- to 360-nm dis tance from the LD, and most (>90%) of the labeling epitopes in the cen tral triple-helical collagenous domain were distributed between the LD and up to 360 nm from it; no specific labelings were observed beyond this area. These results suggest that most (>90%), if not all, of the AF in human skin do not extend perpendicularly into the dermis, but in stead originate and terminate in the LD, forming individual semicircul ar loops that constitute a network of AF.