EVALUATION OF VARIOUS CYTOKINES (IL-6, IFN-ALPHA, IFN-GAMMA, TNF-ALPHA) AS MARKERS FOR ACUTE BACTERIAL-INFECTION IN SWINE - A POSSIBLE ROLEFOR SERUM INTERLEUKIN-6

A total of 64 specific pathogen free pigs were divided into eight expe rimental groups. Pigs in Group I served as non-infected controls while the other 56 pigs were infected intranasally with approximately 7 x 1 0(8) CFU of Actinobacillus pleuropneumoniae serotype 2 (strain 700/89) in 1 mi saline. When more than 25% of the infected animals showed cli nical signs of disease, i.e. 20 h post infection, 48 of the infected p igs were treated with different antibiotics (8 pigs per group), leavin g 8 infected animals untreated, Serum samples collected 0, 10, 20, 28 and 44 h, and 3, 4, 7, 13 and 17 days post infection were analysed for their content of interferon (IFN)-alpha, IFN-gamma, tumor necrosis fa ctor (TNF)-alpha by immunoassays and interleukin-6 (IL-6) by a bioassa y, In addition, the development of specific antibodies was determined in sera. Among the cytokines analysed, the experimental infection only induced detectable serum levels of IL-6, The appearance of IL-6 posit ive animals coincided with the onset of clinical signs of disease and increased body temperatures. Varying levels of IL-6 (range, 1-220 U ml (-1)) were detected in serum from a majority of the infected pigs (80% ). In general, the highest levels of IL-6 were detected in serum colle cted for 10 or 20 h after infection. Among the animals not treated wit h antibiotics, the number of pigs displaying IL-6 in serum continued t o increase until 28 h post infection and then declined. The duration o f the IL-6 response varied between individuals and lasted from eight h ours to three days. Treatment with antibiotics that ceased the infecti on also terminated the IL-6 production in most of the pigs. In a pilot field survey, IL-6 was detected in an approximately 30% of serum samp les collected from conventional reared pigs before allocation to finis hing units. Thus, serum IL-6 seems to be a potential marker for ongoin g bacterial infections in swine. (C) 1998 Elsevier Science B.V. All ri ghts reserved.