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

The aim of this study was to evaluate the immune responses to intranasal andintrapulmonary vaccinations with the attenuated Mycoplasma hyopneumoniae(Mhp) 168 strain in the local respiratory tract in pigs. Twenty-fourpigs were randomly divided into 4 groups: an intranasal immunization group, anintrapulmonary immunization group, an intramuscular immunization group and a controlgroup. The levels of local respiratory tract cellular and humoral immune responses wereinvestigated. 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 andtrachea were higher after intranasal vaccination (P<0.01) than in thecontrol group. Interestingly, intrapulmonary immunization induced much stronger immuneresponses than intranasal immunization. Intrapulmonary immunization also significantlyincreased the secretion of IL-6 and local specific sIgA and the numbers of IgA- andIgG-secreting cells. The levels of IL-10 and interferon-γ in the nasal swab samples andthe numbers of CD4⁺ and CD8⁺ T lymphocytes in the lung and hilarlymph nodes were significantly increased by intrapulmonary immunization compared withthose in the control group (P<0.01). These data suggest thatintrapulmonary immunization with attenuated Mhp is effective in evokinglocal cellular and humoral immune responses in the respiratory tract. Intrapulmonaryimmunization with Mhp may be a promising route for defense againstMhp in pigs.