Ultrastructural immunocytochemical localization of type I procollagen in cultured human fibroblasts.

An immunoelectron microscopic study of cultured human fibroblasts was performed with antibody specific for the carboxyl propeptides of human type I procollagen (Goldberg et al., 1985). In cells permeabilized with detergent, the unlabeled antibody peroxidase-antiperoxidase method localized the antigen in the rough endoplasmic reticulum, in the Golgi complex, and upon the plasma membrane. Immunostained thread-like periodic fibrillar aggregates within cytoplasmic vacuoles were not apparent. Extracellular fibrils 20-80 nm in thickness were diffusely and heavily stained. Immunostaining also defined a thin extracellular periodic fibril (diameter 10-20 nm; axial period 53.7 nm +/- 6.5 S.D.). These data are discussed in terms of current views of procollagen secretion and collagen fibrillogenesis.