Toll-like receptor activation of equine mesenchymal stromal cells to enhance antibacterial activity and immunomodulatory cytokine secretion.
Authors: Pezzanite Lynn M, Chow Lyndah, Johnson Valerie, Griffenhagen Gregg M, Goodrich Laurie, Dow Steven
Journal: Veterinary surgery : VS
Summary
# Editorial Summary Mesenchymal stromal cells (MSCs) have emerged as a promising therapeutic tool for treating equine infections, yet their inherent antimicrobial capacity remains limited. Pezzanite and colleagues investigated whether pre-stimulating bone-marrow-derived MSCs with specific immune receptor agonists—namely TLR-3 (polyinosinic:polycytidylic acid), TLR-4 (lipopolysaccharide), and NOD-like receptor activators—could enhance their antibacterial and immunomodulatory properties in vitro. Using conditioned media from activated MSCs harvested from three horses, the team measured bactericidal activity against multidrug-resistant *Staphylococcus aureus*, both in planktonic and biofilm states, alongside production of antimicrobial peptides (cathelicidin/LL-37) and pro-inflammatory cytokines (IL-8, MCP-1). TLR-3 activation with polyinosinic:polycytidylic acid proved most effective, significantly reducing viable planktonic bacterial colonies, suppressing biofilm formation by up to 80% (p = .001), and enhancing neutrophil phagocytosis of bacteria (p = .009). Optimisation of culture conditions—particularly reducing serum concentration to 1–2.5%—substantially increased cathelicidin/LL-37 production and MCP-1 secretion, which promotes neutrophil recruitment. These findings suggest that pre-treating MSCs with TLR-3 agonists before clinical application could substantially improve their efficacy against resistant soft-tissue infections, offering farriers and veterinarians a potential adjunct strategy where antibiotic options are exhausted or contraindicated.
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Practical Takeaways
- •TLR3-activated MSC therapy may offer a novel approach to treating antibiotic-resistant bacterial infections in equine wounds and soft tissue injuries, particularly those involving biofilm-forming organisms
- •Culture conditions significantly affect MSC immunomodulatory output—serum reduction enhances antimicrobial peptide production, suggesting standardized protocols are essential for clinical translation
- •MSC activation appears to work synergistically with the horse's own immune system (neutrophil enhancement), potentially making it effective even against resistant pathogens
Key Findings
- •TLR3 agonist (pIC) stimulation of equine MSCs significantly enhanced bactericidal activity against planktonic S. aureus (p=0.004) and suppressed biofilm formation (p=0.001)
- •pIC-activated MSCs increased monocyte-chemoattractant-protein (MCP-1) secretion (p<0.0001) and cathelicidin/LL-37 production, with enhanced effect at reduced serum concentrations (1-2.5%)
- •TLR3-activated MSC-conditioned media enhanced neutrophil bacterial phagocytosis (p=0.009), suggesting immunomodulatory synergy
- •Optimal pIC activation protocol: 2×10⁶ cells/ml, 2-hour stimulation, 10 μg/ml concentration with reduced serum media