Evidence of cell-mediated immune response and specific local mucosal immunoglobulin (Ig) A production against Lawsonia intracellularis in experimentally infected swine.

The purpose of this study was to detect cell-mediated and local humoral immune responses to Lawsonia intracellularis in pigs inoculated with a pure culture of the pathogenic isolate or with an intestinal mucosa homogenate. Twenty-four 5-week-old pigs were inoculated with a pure culture of L. intracellularis (n = 10), an intestinal mucosa homogenate from proliferative enteropathy diseased pigs (n = 10), or a control solution (n = 4). All animals were bled 0, 7, 14, and 20 d post-inoculation (pi). Serum was tested for immunoglobulin (Ig) G against L. intracellularis and for the production of interferon (IFN)-gamma by peripheral blood mononuclear cells (PBMC) after inoculation with L. intracellularis total proteins. Delayed-type hypersensitivity (DTH) reactions were evaluated 24 and 48 h after intra-dermal injection of different concentrations of L. intracellularis antigen 20 d pi. All animals were euthanized on day 22, intestinal lavages of ileum and IgA titrations were done. Weak IFN-gamma production was detected in 1 pig from the pure culture group and 2 pigs from the mucosal homogenate group 14 d pi, and in 2 animals from both groups 20 d pi. All pigs, in both inoculated groups, were seropositive for IgG on day 20. Inoculated pigs from both groups showed very weak dose-dependent DTH reactions, which were more evident at 24 h than 48 h pi. Eight pigs from the pure culture group and 7 from the mucosa homogenate group had detectable IgA titers in the intestinal lavage 22 d pi. In conclusion, specific local intestinal humoral and weak cell-mediated immune responses can be detected in pigs experimentally infected with L. intracellularis.