Identification of Interleukin-1, Tumor Necrosis Factor-[alpha], and Interleukin-6 Expression in Lungs from Pigs Naturally Infected with Mycoplasma hyopneumoniae by In situ Hybridization

The detection and distribution of interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α) and IL-6 were studied, by in situ hybridization with a non-radioactive digoxigenin-labeled probe, in formalin-fixed, paraffin-embedded lung tissue from 10 pigs naturally infected with Mycoplasma hyopneumoniae. The morphology of host cells was preserved despite the relatively high temperature required during the incubation procedure. Examination of three serial sections from each of the 10 lung samples showed that the three cytokines closely resembled each other in respect of cellular distribution. Three inflammatory cytokines are expressed in response to M. hyopneumoniae infection, with IL-6 localized primarily to peribronchiolar lymphoid hyperplastic tissues, and both IL-1 and TNF-α expressed in alveolar macrophages. Although statistically non-significant, IL-1 (r=0.5744, p=0.0883) showed potentially important correlation with histopatholgical lesions. No other potentially clinically important correlations (r>0.30) were observed between any of the other cytokines (TNF-α r=0.2045, p=0.5603 and IL-6; r=-0.06607, p=0.8651) and histopathological lesion score. The results suggest that inflammatory cytokines are associated with the development of pneumonia in M. hyopneumoniae infection and may contribute to disease severity.