Little is known about the immune response during infection of pigs with Mycoplasma hyopneumoniae (Mhp). To further understand this important porcine respiratory pathogen, we examined the interleukin-18 (IL-18) response in experimentally infected piglets. We found that large amounts of IL-18 were produced in the bronchoalveolar lavage fluids (BALF) of pigs experimentally infected with Mhp. However, interestingly, the concentration of interferon-γ (IFN- γ) in the same BALF was negatively correlated with that of IL-18. The antibody response against Mhp was associated with the IL-18 concentration in the BALF. Immunohistochemical staining revealed that both IL-18 and the IL-18 receptor α chain (IL-18Rα) were present in macrophages and plasma cells in the lungs of Mhp-infected pigs. Lung mononuclear cells isolated from pneumonic lesions secreted IL-18 and prostaglandin E2 in vitro, and prostaglandin E2 production was enhanced by stimulation with IL-18. These results indicate that IL-18 produced in the pig lung contributes to the development of innate and acquired immune responses against Mhp as a proinflammatory cytokine, rather than as an IFN-γ inducing factor, and may be involved in immunomodulation in pigs.
(Research Team for Advanced Biologicals, TEL +81-29-838-7708)
