Identifying the immunoglobulin G transporter in equine tissues: A look at the neonatal Fc receptor.
Authors: Guenther M C, Borowicz P P, Hirchert M R, Semanchik P L, Simons J L, Fridley J, White-Springer S H, Hammer C J
Journal: Journal of equine veterinary science
Summary
# Editorial Summary The neonatal Fc receptor (FcRn) orchestrates critical immune functions by transporting immunoglobulin G across cellular barriers, regulating serum IgG concentrations, and facilitating antigen presentation—yet its tissue distribution and expression patterns in horses remained unexplored until this 2024 investigation. Researchers collected samples from six horses across multiple anatomical sites (respiratory tract, gastrointestinal tract, visceral organs, cornea, and synovial membranes of stifle and carpal joints), then quantified FcRn presence using immunofluorescence microscopy and qPCR analysis to assess both protein abundance and mRNA expression. FcRn distribution proved highly heterogeneous: joint synovium and respiratory tissues showed the highest protein abundance, gastrointestinal tissues expressed moderate levels, and other visceral organs demonstrated minimal fluorescence; conversely, liver and kidney exhibited the highest mRNA transcription whilst stomach and cornea showed the lowest. These findings are particularly relevant for practitioners seeking to understand passive transfer of immunity in foals, mucosal immunity in the respiratory and intestinal systems, and potential therapeutic targeting of IgG-mediated responses in joint diseases—opening avenues for investigating whether regional FcRn expression influences disease susceptibility or recovery trajectories in different tissues.
Read the full abstract on PubMed
Practical Takeaways
- •FcRn distribution patterns in equine tissues suggest tissue-specific roles in IgG transport and immune function that may influence passive immunity transfer and local immune responses
- •Differential FcRn expression in joint tissues and respiratory tract could have implications for understanding IgG-mediated immunity in these high-disease-burden sites in horses
- •This foundational work establishes baseline tissue localization data needed to interpret how FcRn dysfunction might affect disease susceptibility or treatment response
Key Findings
- •FcRn abundance varied significantly across equine tissue types (P < 0.01), with joint synovium and respiratory tract showing highest immunofluorescence relative to visceral organs
- •Liver and kidney tissues expressed the highest FCGRT transcript levels by qPCR, while stomach and cornea expressed the lowest
- •Gastrointestinal tract tissues demonstrated moderate FcRn expression, suggesting involvement in IgG transport across this barrier