An attempt at quantitation of procollagens I and III and of collagen IV in tooth sections by exposure to the corresponding antibodies followed by 125I-protein A and radioautography.

The immunoreactivity of procollagen types I and III and of collagen type IV was detected in frozen sections of the growing apical end of rat incisor teeth by an indirect method making use of protein A. The sections were exposed to affinity-purified antibodies against these substances. The bound antibodies were then detected by incubation with radioiodinated protein A, followed by radioautography. This immunoradioautographic approach yielded preparations with low background, in which the reactions could be quantitated by counts of silver grains. The distribution of the radioautographic reactions was essentially the same as that previously observed with direct and indirect peroxidase methods, that is, procollagen I antigenicity predominated in odontoblasts and predentin, with minor amounts in periodontal tissue and pulp; procollagen III antigenicity was present in periodontal tissue and, to a lesser extent, in the pulp; and collagen IV antigenicity was restricted to basement membranes. Moreover, grain counts provided quantitative support for the conclusions on the distribution of procollagen I and III antigenicity.