Lawsonia intracellularis-specific interferon γ gene expression by peripheral blood mononuclear cells in vaccinated and naturally infected foals

The cell-mediated immune response to Lawsonia intracellularis, the agent of equine proliferative enteropathy (EPE), was investigated in vaccinated and naturally infected foals. Interferon (IFN)-γ gene expression was determined in peripheral blood mononuclear cells collected from vaccinated (n = 6) and control foals (n = 6) every 30 days for 180 days following first vaccine administration, and from clinically affected foals (n = 16) within 7–10 days of diagnosing EPE. Seroconversion (immunoperoxidase monolayer assay titer ⩾60) occurred in 5/6 vaccinated foals between 60 and 90 days following the first vaccine administration and these foals remained seropositive for the remaining study period. IFN-γ gene expression in all vaccinated foals was significantly higher (P < 0.05) on days 60–180 following first vaccine administration compared to IFN-γ gene expression in control foals. When IFN-γ gene transcription was compared between naturally infected and vaccinated foals, a significant difference (P < 0.05) was observed only for day 0.