Comparison of immune responses to intranasal and intrapulmonary vaccinations with the attenuated Mycoplasma hyopneumoniae 168 strain in pigs

Abstract

The aim of this study was to evaluate the immune responses to intranasal and intrapulmonary vaccinations with the attenuated Mycoplasma hyopneumoniae (Mhp) 168 strain in the local respiratory tract in pigs. Twenty-four pigs were randomly divided into 4 groups: an intranasal immunization group, an intrapulmonary immunization group, an intramuscular immunization group and a control group. The levels of local respiratory tract cellular and humoral immune responses were investigated. The levels of interleukin (IL)-6 in the early stage of immunization (P<0.01), local specific secretory IgA (sIgA) in nasal swab samples (P<0.01); and IgA- and IgG-secreting cells in the nasal mucosa and trachea were higher after intranasal vaccination (P<0.01) than in the control group. Interestingly, intrapulmonary immunization induced much stronger immune responses than intranasal immunization. Intrapulmonary immunization also significantly increased the secretion of IL-6 and local specific sIgA and the numbers of IgA- and IgG-secreting cells. The levels of IL-10 and interferon-γ in the nasal swab samples and the numbers of CD4(+) and CD8(+) T lymphocytes in the lung and hilar lymph nodes were significantly increased by intrapulmonary immunization compared with those in the control group (P<0.01). These data suggest that intrapulmonary immunization with attenuated Mhp is effective in evoking local cellular and humoral immune responses in the respiratory tract. Intrapulmonary immunization with Mhp may be a promising route for defense against Mhp in pigs.

Fig. 1.

Cytokine levels (A, IL-6; B, IL-10; C, IFN-γ) in nasal swabs collected three and 5 days after the first inoculation. Results are presented as the mean ± SEM. The level of significance is identified by the P value. Capital letters indicate differences at P<0.01, and small letters indicate differences at P<0.05

Fig. 2.

The changes in the distribution and numbers of CD4+ and CD8+ T lymphocytes in the lung (A, C) and hilar lymph nodes (B, D). Results were presented as mean ± SEM. The level of significance is identified by the P value. Capital letters indicate differences at P<0.01, and small letters indicate differences at P<0.05.

Fig. 3.

The changes in the distribution and numbers of IgA- and IgG-secreting cells in the nasal mucosa (A, C) and trachea (B, D). Results are presented as the mean ± SEM. The level of significance is identified by the P value. Capital letters indicate differences at P<0.01, and small letters indicate differences at P<0.05.

Fig. 4.

The S/P values of anti-Mhp-specific SIgA in the nasal secretions collected at 7, 14, 21, 28 and 35 days after the first inoculation. Results are presented as the mean ± SEM. The level of significance is identified by the P value. Capital letters indicate differences at P<0.01, and small letters indicate differences at P<0.05.