Effects of an experimental infection with Actinobacillus pleuropneumoniae on the interferon-alpha and interleukin-6 producing capacity of porcine peripheral blood mononuclear cells stimulated with bacteria, virus or plasmid DNA

The effect of a bacterial infection on interferon-alpha (IFN-alpha) and int erleukin-6 (IL-6) production by porcine cells was studied in specific patho gen-free (SPF) pigs, infected intranasally with Actinobacillus pleuropneumo niae serotype 2. Three experimental groups of five pigs were used: infected non-treated pigs, infected pigs that were treated with enrofloxacin at dis ease onset, and non-infected, non-treated control pigs. Blood samples were collected from all pigs on the day of infection and on days 1, 4. 7, 13 and 17 post-infection. Sera were analysed for presence of antibodies to A. ple uropneumoniae and for the cytokines IL-6 and IFN-alpha. Ability to produce these cytokines was tested in vitro using whole blood cultures stimulated w ith inactivated virus (Aujeszky's disease virus infected porcine kidney cel ls (ADV/PK-15)), inactivated bacteria (A. pleuropneumoniae) or bacterial pl asmid (pcDNA3). All cytokine inducers were used neat or pre-incubated with the transfectious agent lipofectin. IL-6 appeared in the serum of all infec ted nontreated animals but no IFN-alpha was found in the serum of any of th e experimental pigs. Accordingly, the bacteria induced a substantial IL-6 b ut hardly any IFN-alpha production when tested in vitro. However, following incubation with lipofectin. the inactivated bacteria as well as pcDNA3 bec ame efficient inducers of IFN-alpha in whole blood cultures. The increased TFN-alpha production, previously recorded in vitro during the acute phase o f infection with A. pleuropneumoniae, was confirmed using lipofected plasmi d DNA and it was indicated that leukocytes obtained from infected but appar ently cured animals also exhibited an increased production of IFN-alpha. Th us, even mild/subclinical bacterial infections may affect cytokine producti on in pigs. (C) 2001 Elsevier Science B.V. All rights reserved.