Immunoelectron microscopic localization of human type III collagen in human gastrointestinal carcinomas

Ultrastructural immunolocalization of human type III collagen/procollagen was investigated in 28 cases of human gastrointestinal carcinoma by the pre-embedding method using a monoclonal antibody. In addition to immunoreactivity on collagen fibers, amorphous or finely fibrillar immunoreactive substances were observed in the extracellular matrix adjacent to the plasma membrane and in the cisternae of rough endoplasmic reticulum (rER). These substances were considered to represent type III procollagen and/or collagen before fiber formation. Cytoplasmic recesses containing immunoreactive fibers were also observed. These findings related to collagen production were detected in stromal fibroblasts in 16 of 28 cases and in carcinoma cells in six of 28 cases. The positivity rate of these findings was lower in diffuse-type gastric carcinoma. The present study thus clarified further details of collagen production and secretion, and revealed that carcinoma cells may also be involved in the production of stromal collagen in some cases as well as stromal fibroblasts.