7 S collagen: a method for the measurement of serum concentrations in man.

A radioimmunoassay was developed for the detection of 7 S collagen, a basement membrane component derived from type IV collagen, in sera of patients. Two forms of 7 S collagen were isolated by limited collagenase digestion of type IV collagen from bovine placenta. Antisera against both forms were raised in rabbits. The antigens were labeled by conjugation with the Bolton Hunter reagent or by the Chloramine T method. Free and bound antigen were separated using a second antibody directed against rabbit-IgG. Serum concentrations of 7 S collagen ranged from 5-14 micrograms/l. Serum levels of 7 S collagen were increased in diabetic patients as compared to normal subjects.