Histochemical investigation of connective tissue in cases of acute rheumatism.

The connective tissue is the chief place where the pathological rheumatic process takes place. The changes mainly affect its intercellular components. On the basis of this localization of the pathological lesions, rheumatism has been included among the so-called collagen diseases (Klemperer, 1950). The mechanism of development of the pathological processes in the intercellular substance of connective tissue can be understood only when there is a clear idea of the nature, structure, and correlations of collagen and the amorphous cementing substance, both of which play a principal role in the development of the rheumatic process. The investigations made in recent years with the aid of physical, chemical, and histochemical methods have considerably advanced our concepts about collagen as a protein-polysaccharide complex (Randall, 1953; Randall, Both, Burge, FittonJackson, and Kelly, 1955; Jackson, 1954, 1957; Partridge, 1948; Orekhovich, 1952; Schmitt, Gross, and Highberger, 1955; Gross, Highberger, and Schmitt, 1955; Banga, Balo, and Szabo, 1956), and have helped in elucidating the processes taking place in the connective tissue in rheumatism. However, the concept that collagen was a monophasic system has hindered researchers from correctly analysing the observed phenomena. A group of Soviet investigators have obtained new data on the structure of collagen; by biochemical, histochemical, roentgenological, and electronmicroscopic studies they have proved that collagen is a multi-phasic system consisting of many components (Tustanovsky, Seidess, Orlovskaya, and Michailov, 1954; Seidess, Tustanovsky, and Orlovskaya, 1955; Orlovskaya, Seidess, and Tustanovsky, 1956). Collagen has therefore been divided into two phases: soluble (procollagen) and insoluble (collastromine). Obtained by precipitation from a solution, procollagen has all the properties of collagen fibrils (of collagen): it turns red when it is stained by Van Gieson stain, and its roentgenogram shows the characteristic interplane intervals of 2-9 A and 11-0 A. Under the electron microscope it shows the same transverse bands. In a roentgenogram, collastromine shows no ring at 2 9 A which is characteristic for collagen; it has no periodicity, does not turn red with Van Gieson stain, and shows a distinct metachromasia; staining with silver reveals argyrophilic fibres. The results of fractioning show collagen as at least a bi-phasic system; the known features of collagen in toto are determined by its content of procollagen. Both procollagen and collastromine consist of many components. Collastromine contains polysaccharides and argyrophilic and non-argyrophilic proteins. The last make up the main mass of collastromine, and its amino acid content is almost identical with that of procollagen. Procollagen has been separated into its protein and polysaccharide components. The polysaccharides include hyaluronic-acid-type polysaccharides and chondroitin-sulphate. After the separation of the polysaccharides, procollagen loses its transverse bands and is precipitated in the form of amorphous threads which, however, retain the collagen structure in the roentgenogram. The reunion of individual polysaccharides with proteins and the subsequent dialysis of this compound again leads to the formation of fibrils with characteristic bands. Thus, it may be considered that the presence of transverse bands is connected with the combination of polysaccharide with procollagen.