On the immune response in porcine enteric diseases : with special reference to swine dysentery, proliferative enteropathy and PMWS

Sammanfattning: Enteric infectious diseases are a common problem worldwide among pigs. It is important to gain a better knowledge about the pathogeneses of the diseases and the local immune response, in which the intestine has a very important role. The aim of this thesis was to study the immune response in pigs infected with Brachyspira hyodysenteriae, Lawsonia intracellularis or Porcine circovirus type 2 (PCV2) that cause swine dysentery (SD), proliferative enteropathy (PE) and postweaning multisystemic wasting syndrom (PMWS), respectively. For SD and PMWS, material from both experimental infections and field cases were used, whereas material from pigs with PE was available from field cases. The local immune response was studied by analysing the cytokine expression in intestines using the microarray and quantitative PCR techniques. For that purpose a porcine microarray with a limited number of cytokines representing different types of immune response was constructed and evaluated using in vitro stimulated porcine blood mononuclear cells, and porcine intestinal samples. A commercial available genome wide porcine cDNA microarray was applied for screening intestinal samples collected from experimental (PCV2) as well as field (Lawsonia intracellularis) studies. The serum analyses showed that IL-1β, IL-6 and TNF-α were increased during natural SD. In pigs with experimental PMWS, increased mRNA expressions in the intestine for IL-6, IL-10 and IFN-γ were found. The increased mRNA expression for IFN-γ was also observed in field cases. For pigs with PE no differences in cytokine levels in serum or intestine were found between control and case pigs. cDNA microarray screening of intestinal samples from pigs with PE indicated that an uncomplicated infection with L intracellularis does not evoke an immune response and that the severe clinical signs of haemorrhagic diarrhoea can be regarded as a complication to the chronic form. In PCV2-infected pigs a marked up-regulation of interferon-stimulated genes was noticed. Comparison of two different isolates of PCV2 revealed differences in gene expression evoked by the two isolates. Expanded analyses using methods established in the present thesis will provide valuable insight into immune reactions elicited at porcine enteric diseases.