Presence of mononuclear cells in normal and affected laminae from the black walnut extract model of laminitis.

The research article provides evidence of involvement of inflammatory cells in acute laminitis, a condition affecting horses. Specifically, the study investigates the presence and location of certain types of immune cells in the hoof tissue of normal horses and those affected by laminitis induced by black walnut extract.

Objective and Methodology

• The aim of this study was to identify and locate monocytes/macrophages and B and T lymphocytes in the laminar tissue of unaffected horses and those with black walnut extract-induced laminitis.
• Immunohistochemistry was applied on tissue samples from 20 horses – equally distributed into four different groups: control, BWE administered after 1.5 hours, at the onset of leukopenia, and at the onset of lameness.
• The authors used antibodies against CD3, CD20, and CD163 to recognize respective types of cells.

Findings

• Mononuclear cells were found in the laminar tissue of normal horses.
• Most of the CD3- and CD20-positive lymphocytes were localized around the vessels deep within the dermis, but also near the vessels of the primary dermal laminae.
• The CD163-positive macrophages were mostly located in the deep dermis or in dermal laminae.
• Unexpectedly, no changes were found in the number of laminar B or T lymphocytes at any point after BWE administration.
• Significant increases (P=0.0016) in CD163-positive cells were observed in the secondary dermal laminae in the groups administered BWE after 1.5 hours and at the onset of leukopenia, which then returned to normal values in the lameness group.

Conclusions

• The study concludes that lymphocyte and macrophage populations are present in the laminar tissue of even clinically normal horses.
• Administration of BWE caused an increase in CD163-positive macrophages in the secondary dermal laminae.
• The authors suggest that both the native population of mononuclear cells in the host tissue and the incoming monocytes could play a significant role in the pathophysiological changes that lead to laminar injury.