Immunoquantification of type I, III, IV and V collagen in small samples of human lung parenchyma

The involvement of collagen in pathological conditions underscores the need for sensitive, collagen type-specific assays. A method for the quantification of different types of collagen in lung has been developed. Human lung parenchyma is digested with cyanogen bromide which results in almost complete solubilization of collagen to type-specific collagen peptides. The peptides are quantified using inhibition enzyme immunoassays with type-specific antibodies. The 50% inhibition value for the type I collagen assay is 1 microgram type I collagen peptides, for the type III collagen assay 350 ng type III collagen peptides, for the type IV collagen 200 ng type IV collagen peptides, and for the type V collagen assay 50 ng type V collagen peptides. Using less than 1 mg lyophilized human parenchymal lung tissue it was established that the amount of collagen/mg dry tissue (+/- SD, n = 10) is 84.6 +/- 16.1 micrograms for type I collagen, 26.6 +/- 10.3 micrograms for type III collagen, 9.6 +/- 2.0 micrograms for type IV collagen and 1.8 +/- 0.3 micrograms for type V collagen. The procedure is useful for the quantification of different types of collagen, including minor collagens, and requires only minimal sample preparation.