Intracellular collagen in experimental arthritis in rats.

In recent years the development ofimproved autoradiographic techniques and in particular electron micro-autoradiography (Caro and von Tubergen 1962) has led to a better understanding of collagen fibre production by fibroblasts (Revel and Hay 1963, Ross and Benditt 1965). It is now generally accepted that collagen fibres are formed outside the cell by an extracellular aggregation of soluble collagen precursors (Gross 1956, Revel and Hay 1963, Goldberg and Green 1964, Ross and Benditt 1965). It appears that the soluble precursor (tropocollagen) is released from the cell probably through the vesicles along the cell border. Once extracellular, the tropocollagen aggregates into fibrils which gradually increase in diameter until the definitive collagen fibres are formed. Experiments on rats with an induced adjuvant polyarthritis have shown certain unusual features in the cells of the proliferating granulation tissue excised from about the affected joints. Cells, which had the electron microscopic characteristics of fibroblasts, appeared to contain numerous inclusions, and prominent among these inclusions were bundles of collagen fibres. To determine the origin of these fibres the synthesis of collagen by these cells was studied by autoradiographic techniques, using tritiated proline as a label.