[Experimental erysipelas in different species as a model for systemic connective tissue disease. II. The chronic...

In part I of this paper (Schulz et al., 1975) it was shown that in the initial phase of experimental erysipelas a transition from the vascular processes to a systemic connective tissue reaction can be demonstrated in different species. It is the purpose of this paper to describe the chronic phase of the disease with special emphasis on polyarthritis.

12 spontaneously diseased and 22 experimentally infected pigs were used in experiments to study the pathogenesis of the disease. In addition, 74 Wistar rats and 148 Sprague-Dawley rats were used in the experiments. All experimental animals were specific-pathogen-free and were parenterally infected with the standardized E. insidiosa serotype B strain T 28. The observation period for the pigs was up to 2 years, for the rats up to 11 months. The methods used for pathohistological and electron microscopical studies are described in part I. Immunihistological studies were carried out on synovial tissue with peroxidase-conjugates of goat-anti-pig-IgG, goat-anti-pig-IgM, pig-collagen, E. insidiosa-homogenate and heat-aggregated-pig-IgG. Furthermore, goat-anti-pig-IgG and rabbit-anti-pig-C3 conjugated with FITC were used. Passive hemagglutination tests and Latex agglutination test (Singer and Plotz) were performed to demonstrate rheumatoid factors and collagen antibodies.

Polyarthritis occurred in pigs between the 4th and 10th day p.i. and between the 4th and 8th day p.i. in nearly 100% of the infected rats. Fibrinous exudation, proliferation and destruction with pannus formation are marked in most of the joints examined during the first three months. Fibrosis begins 30 days p.i. in the rats' joints and is most severe in both species between the 5th and 8th month. 3 types of lining cells may be differentiated electron microscopically: A (M) cells, B (F) cells and an intermediate form which is found in both species most frequently. Swelling of the endothelial cells together with constriction of the lumen and thickening of the basal membrane occurs in the capillaries.

A comparison of chronic erysipelas polyarthritis in pigs and rats with rheumatoid arthritis of men reveals many morphological and immunological similarities between the two diseases. Systemic connective tissue activation manifests itself in organs predilected for rheumatic changes, such as heart valves, endocardium and joints. The possible prepetuation of the processes by specific or nonspecific immunomechanisms or by deposits of fibrin is discussed. In addition, experimental erysipelas is reproducible in nearly 100% of the animals given one single subcutaneous application of one defined bacteria strain. Therefore too, erysipelas is suited as an animal model for human rheumatic diseases.