170 J. Øvrebø Bohnhorst et al. tween 3 and 18 months, found markedly ele- vated IL-6 during acute episodes of the disease, but no TNF-α. The disease follows a remittant course with episodes of clinical disease and dis- ease-free intervals. Clinical signs include fever (>40 °C), weight loss and severe neck pain. Sick dogs improved dramatically upon treatment with corticosteroids and the clinical improve- ment was accompanied by a decrease in IL-6 activity. Withdrawal of corticosteroid treatment caused reappearance of clinical signs and high serum IL-6 within few days. These results sup- port a role for IL-6 in the pathogenesis of JPS. An inherited recurrent fever of unknown origin with renal amyloidosis in Chinese Shar-pei dogs was also associated with elevated IL-6 (Rivas et al. 1992). In our material 7/20 dogs were ANA positive, 1/20 was anti ENA positive, 2/13 were RF pos- itive and 10/13 presented with elevated Il-6. Comparing the results of the individual patients (Table 1), it is evident that they differ much and do not present uniform patterns neither within nor between the groups.. Among 9 dogs tested for all parameters, one was ANA and another was RF positive only, while a third was ANA positive and showed elevated IL-6 level. Six dogs presented elevated IL-6 only, which indi- cate a role for IL-6 in the pathogenesis of most cases in this study. This and the diagnostic sig- niﬁcance of this factor in immune-mediated fever in dogs are aspects that should be looked at in the future. One breton and one German shepherd dog were RF positive, but none of them presented signs of rheumatoid arthritis. Detection of RF in ca- nine sera by latex agglutination technique is commonly used in screening, but the test is not speciﬁc for diagnosing rheumatoid arthritis. Circulating immune complexes produced in other inﬂammatory diseases may to some ex- tent bind to the IgG coated latex particles (Thoren-Tolling 1991). Acta vet. scand. vol. 43 no. 3, 2002 Acknowledgement We thank dr. Terje Espevik for help with TNF-α and IL-6 analyses. References Aarden LA, de Groot ER, Feltkamp TE: Immunology of DNA. III. Crithidia luciliae, a simple substrate for determination of anti ds-DNA with the im- munoﬂuorescence technique. Ann. N Y Sci 1975, 254, 505-515. Aarden LA, de Groot ER, Shaap OG, Lansdorp PM: Production of hybridoma growth factor by human monocytes. Eur. J. Immunol. 1987, 17, 1411- 1416. Bennett D & Kelly DF: Immune-based non-erosive inﬂammatory joint disease of the dog. II. Pol- yarthritis/Polymyositis syndrome. JSAP. 1987, 28, 891- 909. Bennet D: Diagnosis of pyrexia of unknown origin. In Practice 1995, 17, 470-481. Bennet D & May C: Joint diseases of dogs and cats. In: Textbook of veterinary internal medicine. SJ Ettinger & EC Feldman eds. WB Saunders 1995 pp 2063-2072. Brakenhoff JPJ, de Groot ER, Evers RF, Pannekoek H, Aarden LA: Molecular cloning and expression of hybridoma growth factor in Escherichia coli. J. Immunol. 1987, 139, 4116-4121. Carter SD, Barnes A, Gilmore WH: Canine rheuma- toid arthritis and inﬂammatory cytokines. Vet Im- munol Immunopathol 1999, 69, 201-214. Dunn KJ & Dunn JK: Diagnostic investigations in 101 dogs with pyrexia of unknown origin. JSAP 1998, 39, 574-580. Espevik T & Nissen-Meyer J: A highly sensitive cell line, WEHI 164 clone 13, for measuring cyto- toxic factor/tumor necrosis factor from human monocytes. J. Immunol. Methods 1986, 95, 99- 105. Feldman B: Fever of undetermined origin. Com- pendium on continuing education for the practic- ing veterinarian 1980, 2, 970-977. Hansson H, Trowald-Wigh G, Karlsson-Parra A: De- tection of antinuclear antibodies by indirect im- munoﬂuorescence in dog sera: Comparison of rat liver tissue and human epithel-2 cells as antigenic substrate. J. Vet. Int. med. 1996, 10, 199-203. Hansson H & Karlsson-Parra A: Canine antinuclear antibodies: Comparison of immunoﬂuorescence staining pattern an precipitin reactivity. Acta vet. Scand. 1999, 40, 205-212.