Characterisation of TLR7/8 in equine pulmonary alveolar macrophages

Purpose of the study: In both human and equine athletes, viral infections are common causes of respiratory diseases and of a sudden deterioration of expected performances. In both species, the underlying mechanisms are still unclear, and an involvement of Toll-Like Receptors (TLRs), a fundamental link between innate and adaptive immunity, has been advocated. Our objectives were to verify the presence of TLR7 and TLR8, responsible for the early anti-viral response in mammals, in equine pulmonary alveolar macrophages (PAMs) and to assess their function through specific stimulation.

Methods used: Equine PAMs were collected by broncho-alveolar lavage (BAL), isolated by adherence and stimulated with specific TLR7/8 ligands (an imidazoquinoline compound and single-stranded RNA), mimicking a viral attack. The expression of TLR7/8 was evaluated by rt-PCR and the ligand-induced production of cytokines (type I-IFNs and TNF-α) was assessed via ELISA.

Summary of results: Our study demonstrated the expression of TLR7/8 in equine PAMs.
QPCR analyses showed a high relative expression of genes coding for TLR7 and TLR8 on equine PAM. Stimulation with specific TLR7/8 ligands resulted in significantly up-regulated production of IFN-β and TNF-α, thereby confirming that TLR7/8 are functional in equine PAMs and that they play a role in the early pulmonary antiviral response.

Conclusions: This study shows that TLR7 and TLR8 are present and functional in equine PAM and that they could play a role in the early pulmonary antiviral response. In terms of future perspectives, it is interesting to suggest that the extensively demonstrated efficacy of TLR7 and TLR8 synthetic ligands in the treatment of viral diseases in human medicine could motivate the pursuit of clinical trials in the equine patient for the therapeutic management or prevention of viral respiratory infections.