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Pigs selected for high (H) or low (L) combined antibody and cell-mediated immune response were infected with Mycoplasma hyorhinis. Following the infection, arthritis was more severe in the H pigs, while pleuritis and peritonitis were more severe in the L pigs. Since Mycoplasma infections in pigs often cause just mild signs, indicators of the inflammatory response may aid diagnosis of such infections. In addition, data about the genetic influence on inflammatory response indicators are scanty in the pig. The objectives of the study were therefore: firstly, to determine interferon-alpha (IFNalpha) and haptoglobin in M. hyorhinis infected pigs and, secondly, to investigate if the inflammatory response as determined by these indicators was influenced by genetic selection. There was no consistent increase of IFN-alpha in serum following infection. The serum haptoglobin concentration started to increase 3 days post-infection and there was no difference between the two breeding lines. Hence, M. hyorhinis infection in pigs is reflected in increased serum haptoglobin concentration, but no effect of the magnitude of the inflammatory response on this indicator by selection for high or low immune response was observed.

Two murine monoclonal antibodies (mAbs) directed against different epitopes on recombinant porcine interferon-alpha (IFN-alpha) were selected and used to construct a two-site ELISA. This ELISA, when performed in a one-step version, detected about 0.5 units ml-1 of IFN-alpha and showed similar sensitivity but better precision than a cytopathic effect inhibition bioassay. Estimates of IFN-alpha in tissue culture medium by the two assays correlated well. In contrast, one or several factors in porcine serum reduced the sensitivity of the ELISA. Measurements of IFN-alpha in porcine serum was, however, possible in a two-step version of the ELISA, with a sensitivity of about 1 unit IFN-alpha ml-1. Results of ELISA and bioassay agreed, except that the ELISA possibly produced false positive results in two out of a total of 91 sera negative in the bioassay. In addition, one of 23 sera positive in the bioassay was negative in the ELISA.

Pigs were transported from several breeding facilities at the age of 10-12 weeks and regrouped in a fattening farm, specialized in breeding pigs for subsequent slaughter. Blood samples were obtained from the animals just before transport and daily for 17 days after installation in the fattening farm. On each occasion a group of ten animals (170 animals in total) was sampled. The levels of interferon-alpha (IFN-alpha) in serum were measured as antiviral activity in a cytopathic effect inhibition assay. Beginning at day 4 after installation, a significant proportion of sera contained IFN-alpha, with the highest incidence of IFN-alpha positive animals (25%) and IFN-alpha titers on days 5-10. This indicates a high frequency of viral infections in the animals. The in vitro ability of peripheral blood mononuclear leukocytes (PBMCs) to produce IFN-alpha after stimulation by glutaraldehyde-fixed pseudorabies virus-infected PK15 cells and their proliferative response to the T-cell mitogen leukoagglutinin (LA) was also monitored. There was a significant, but moderate decrease in the ability of PBMCs to produce IFN-alpha during the observation period. In contrast, the response to the mitogen LA decreased markedly during the first 5 days, and thereafter remained at the same low level. The proliferative response to LA was significantly lower for PBMCs from serum of IFN-alpha-positive than from IFN-alpha-negative animals. These impaired PBMC responses could indicate a stress-induced immune depression, possibly contributing to the high incidence of viral infections.