Ileal lesion severity at days post-inoculation 21. Panels A and B represent macroscopic lesions in non-infected pigs (NC, black), non-vaccinated Lawsonia intracellularis inoculated pigs (PC, white), and vaccinated Lawsonia intracellularis inoculated pigs (VAC, blue), while panels C through F describe microscopic lesion severity. A Frequency of macroscopic lesion severity score. B Average lesion length (cm) of lesion, if any. C Inflammation score wherein 0 = none/minimal, 1 = mild, 2 = moderate, and 3 = severe. D Proliferation of crypts, wherein 0 = none/minimal, 1 = mild, 2 = moderate, and 3 = severe. E Lesion distribution score, wherein 0 = none, 1 = focal, 2 = multifocal, and 3 = diffuse. F L. intracellularis immunohistochemistry (IHC) scoring, where 0 = no antigen stain, 1 = 1–25% of crypts, 2 = 26–50% of crypts, 3 = 51–75% of crypts, 4 = > 75% of crypts positive for antigen.