Human tissue distribution of novel basement membrane collagen

The authors have defined the specificity of monoclonal antibodies to collagen fragments of basement membrane (BM) and have used these highly specific antibodies to study the human tissue distribution of two novel 28 kd noncollagenous (NC1) peptides (M28 , M28+) compared with those derived from type IV collagen (alpha 1[26 kd] and alpha 2[24 kd] NC1). A limited distribution of the 28 kd peptides was observed in specialized BM of the kidney, eye, cochlea, lung, and brain, whereas type IV collagen is found in all human BM. These novel peptides, which colocalize with each other, are found in BM that also contain type IV collagen but do not, in all cases, colocalize with type IV collagen. The presence of the 28 kd peptides in the BM of the kidney, cochlea, and eye is in keeping with abnormalities involving these components in BM of patients with Alport familial nephritis (FN), who frequently have hearing loss, anterior lenticonus and retinal flecks in addition to renal disease. These 28 kd peptides are distinct, biochemically and immunochemically, from the alpha 1 and alpha 2 chain NC1 peptides of type IV collagen, and represent either peptide fragments of genetically distinct BM collagen molecules or additional molecules originating from the same gene family as type IV collagen.