Presence of mononuclear cells in normal and affected laminae from the black walnut extract model of laminitis.
Authors: Faleiros, Nuovo, Flechtner, Belknap
Journal: Equine veterinary journal
Summary
# Editorial Summary: Mononuclear Cell Involvement in Black Walnut Extract-Induced Laminitis Inflammatory cell infiltration has emerged as a key mechanism in acute laminitis pathogenesis, yet the specific timing and location of immune cell involvement in laminar tissue remains poorly characterised. Using immunohistochemistry on archived samples from 20 horses, Faleiros and colleagues mapped the distribution of T lymphocytes (CD3+), B lymphocytes (CD20+) and monocytes/macrophages (CD163+) across four treatment groups: control animals, horses treated with black walnut extract (BWE) at 1.5 hours post-administration, at leucopenia onset (3 hours), and at lameness onset. Whilst T and B lymphocyte populations remained stable throughout the experimental timeline, CD163-positive macrophage numbers increased significantly in secondary dermal laminae at both early timepoints (1.5H and 3H post-BWE), before returning to baseline by the lameness phase—a finding suggesting macrophage activation precedes visible clinical signs. The identification of resident mononuclear cell populations in normal laminae, coupled with evidence of selective macrophage recruitment in early laminitis, indicates that understanding monocyte/macrophage dynamics may be critical for developing preventative or early-intervention strategies. For practitioners, this work underscores the importance of timing in anti-inflammatory protocols, particularly within the first three hours of suspected toxin exposure, when macrophage-driven tissue remodelling appears most active.
Read the full abstract on PubMed
Practical Takeaways
- •Macrophage infiltration in the laminae appears to be an early event in laminitis development, preceding visible clinical lameness, suggesting early inflammatory monitoring may help identify at-risk horses
- •The transient nature of macrophage elevation followed by return to baseline despite ongoing lameness suggests different cellular populations may drive early versus late-stage laminitic damage
- •Understanding the role of resident versus infiltrating mononuclear cells could inform therapeutic strategies targeting inflammation in acute laminitis
Key Findings
- •Mononuclear cells (lymphocytes and macrophages) are present in laminar tissue of clinically normal horses
- •Black walnut extract administration induced significant increases (P=0.0016) in CD163-positive macrophages in secondary dermal laminae at 1.5 and 3 hours post-treatment
- •CD163-positive macrophage numbers returned to baseline values by the time of clinical lameness onset
- •B and T lymphocyte populations did not change at any time point following black walnut extract administration