Expression of interleukin-1 beta in the digital laminae of horses in the prodromal stage of experimentally induced laminitis

Objective-To study expression of interleukin-1beta (IL-1 beta) in the digit al laminae of horses in the prodromal stage of experimentally induced lamin itis. Animals-8 healthy adult horses with no signs of laminitis. Procedure-Black walnut extract was administered via nasogastric tube to 4 h orses, and water was administered to the remaining 4 (controls). Complete b lood counts and physical examinations were performed every 30 minutes after administration of black walnut extract or water. General anesthesia was in duced when total WBC count decreased by 30% in horses given the black walnu t extract and 3 hours after water administration in control horses. The lef t forefoot was perfusion fixed with neutral-buffered 10% formalin, and para ffin-embedded sections of the digit were used for in situ hybridization wit h an equine-specific IL-1 beta probe. Results-IL-1 beta mRNA expression was observed in perivascular cells of the small laminar venules and capillaries in all 4 horses given black walnut e xtract and in interstitial cells remote from the microvasculature in 1 of t he 4. Other cellular components of the laminar tissue and cellular componen ts of the digital arterioles and veins did not exhibit IL-1 beta mRNA expre ssion. Expression of IL-1 beta mRNA was not detected in laminae from contro l horses. Conclusions and Clinical Relevance-Results suggest that IL-1 beta mRNA is e xpressed by perivascular cells in the laminar tissues of horses in the prod romal stage of experimentally induced laminitis. This provides evidence of an inflammatory process during the prodromal stage of laminitis, indicating that local digital proinflammatory cytokine expression may be an initiatin g factor in laminitis.