223 Award Talk: The role of immunoglobulin G in horses: Past, present and future.

Abstract Immunoglobulin G (IgG) plays a vital role in equine immunity, serving as the principal antibody involved in long-term immune protection and pathogen neutralization. Historically, the significance of IgG in horses was first recognized through studies of neonatal isoerythrolysis and failure of passive transfer (FPT) in foals, where inadequate ingestion or absorption of colostrum-derived IgG led to heightened morbidity and mortality. Early research emphasized the necessity of timely colostrum intake and investigated diagnostic and stall-side assays such as the zinc sulfate turbidity, total protein, and radial immunodiffusion to quantify serum IgG levels in neonatal foals. Studies have expanded to examine the influence of maternal health and nutrition during pregnancy and the impact those factors have on colostrum quality, including IgG concentration. In modern times, IgG continues to be a cornerstone of diagnostic and therapeutic strategies, and advances in molecular immunology and monoclonal antibody technology have enabled detailed characterization of IgG subclasses. This has enhanced our understanding of their roles in vaccine response, allergic disease, and chronic infections. A recent key advancement in our understanding of IgG dynamics has been the elucidation of the role of the neonatal Fc receptor (FcRn) in several livestock species. FcRn is responsible for protecting IgG from lysosomal degradation, thereby extending its half-life and maintaining serum IgG levels. This receptor not only underlies the success of passive transfer but also has implications for the design of IgG-based therapeutics. Although our understanding of IgG in horses has significantly advanced over the years, challenges remain, including variability in IgG response due to genetic and environmental factors, limited equine subclass-specific reagents, and the ongoing need to support fundamental functional research to deepen our understanding of IgG biology. Nonetheless, the evolution of IgG research in horses reflects broader trends in veterinary immunology and highlights the antibody’s enduring importance across developmental, diagnostic, and therapeutic categories. Continued multidisciplinary efforts will be crucial to advancing the molecular understanding of IgG mechanisms and leveraging its biological capabilities to optimize equine health.