ABSTRACT. In this study, we investigated the expression of immunoglobulin A (IgA) in porcine salivary gland and its relationship with restraint stress in pigs. IgA was expressed in plasma cells in pig salivary gland, as confirmed by immunohistochemical staining. IgA was also detected in pig saliva itself by ELISA, and salivary IgA levels were increased by a restraint stress. Moreover, there was a circadian rhythm of IgA over the course of a day. These results are the first evidence of IgA expression related to stress in the pig saliva and may make IgA useful as a non-invasive biological marker to evaluate acute stress condition in the pigs.KEY WORDS: IgA, non-invasive biomarker, restraint stress, saliva, salivary glands.

ABSTRACT. In this study, several cytokine responses were investigated during Mycoplasma hyopneumoniae (Mhp) infection using a gnotobiotic infection model. We found that several inflammatory cytokines (IL-1β, IL-8, IL-18, and TNF-α) and an anti-inflammatory cytokine IL-10 were induced from peripheral blood mononuclear cells (PBMC) of germ-free (GF) piglets stimulated with heat killed Mhp whole antigens, but no IFN-γ and IL-4 were induced by Mhp. After the intranasal infection of Mhp, IL-1β, IL-8, IL-18, and IFN-γ were also detected in the broncho-alveolar lavage fluids (BALF). The antigen-specific IFN-γ and IL-10 responses after infection of Mhp were gradually suppressed during Mhp infection as well as non-specific immune response to concanavalin A (ConA) and lipopolysacchalide (LPS) at early stage of infection. These results suggested that Mhp infection modulates the immune response of pigs by inducing several cytokines, and causes immuno-suppression of pigs in a gnotobiotic condition.

Little is known about the detail of the immune response during infection of pigs with Mycoplasma hyopneumoniae (Mhp). To further understand this important porcine 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, the concentration of interferon-gamma (IFN-gamma) in the same BALF was negatively correlated with that of IL-18. The antibody response against Mhp was found to be associated with the IL-18 concentration in the BALF. Immunohistochemical staining revealed that both IL-18 and IL-18 receptor alpha chain (IL-18Ralpha) 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 E(2) (PGE(2)) in vitro, and PGE(2) 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-gamma-inducing factor and may be involved in immunomodulation in pigs.

Interleukin-18 (IL-18) has recently been considered a promising marker of stress responses. In this study, to evaluate IL-18 as a noninvasive stress marker in pigs, we investigated the expression of IL-18 in porcine salivary glands and its presence in saliva, and its dynamics during acute immobilization stress in pigs. IL-18 mRNA was detected robustly in the pig salivary glands by RT-PCR. Immunohistochemical staining of IL-18 protein expression revealed that the expression patterns differed among the three types of salivary glands (parotid, submandibular, and sublingual gland). IL-18 was also detected in pig saliva by ELISA, and a diurnal rhythm with a peak in the afternoon was observed. The IL-18 concentration in saliva was significantly increased during a 60-min acute immobilization stress in thirteen 5-month-old pigs. These results are the first evidence of a stress-related change of IL-18 in pig saliva. Salivary IL-18 may thus become a useful noninvasive marker for the evaluation of acute stress in pigs.