STRUCTURE AND FUNCTION OF A NOVEL BASEMENT MEMBRANE-ASSOCIATED COLLAGEN

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The novel collagen in the present project was defined as a protein specifically recognized by a monoclonal antibody originally developed for type IV collagen fraction from human placenta by pepsinization. The epitope appeared to reside on a polypeptide which contained an unidetified amino acid sequence. The collagen was found to be associated with a restricted basement membrane in the immunohistochemical examination on a vascular basement membrane and at least a portion of the polypeptide was associated with alpha 1(IV) chain, since a sandwith ELISA system using the other monoclonal antibody which recognizes alpha 1(IV) showed a positive reaction to the type IV collagen fraction, while the reaction became negative by treatment with heat or/and SH reagent. Molecular structure and function of the novel collagen was characterized by comparison with other extracellular components in solubility, intact size of the polypeptide, susceptibility to proteases. The study indicated similarity to an alpha chain of type IV collagen; that is 180kD chain was recovered only after treatment with SH reagent and denaturants from human placenta. The monoclonal antibody crossed with a particular sequence of alpha 1(IV) chain weakly. An important observation was that human fetal lung fibroblasts produced and deposited the novel collagen as well as alpha 1(IV) on the cell layer by culture, although human dermal fibroblasts deposited the collagen to a much less quantity from the study using cell-layer ELISA. Immunohistochemical localization indicated that deposition of novel collagen appeared to increase by fibroses of liver or kidney. Serum levels of the complex of the novel collagen as determined by ELISA were increased in patients with liver cirrhosis.