In a pioneering study published in Nature Microbiology Dr. Oriol Sunyer and a team from the University of Pennsylvania’s School of Veterinary Medicine and the University of New Mexico have identified an unexpected key player in gut health: secretory immunoglobulin M. While secretory immunoglobulin A has long been recognized for its role in maintaining gut bacterial balance this research reveals that sIgM may be equally if not more important in preserving gut health and overall wellness.

Secretory immunoglobulins antibodies found on mucosal surfaces regulate the colonization composition and metabolic activity of the gut microbiome. Traditionally sIgA in mammals and secretory immunoglobulin T (sIgT) in fish were considered the primary regulators of microbial homeostasis. However Sunyer’s team challenges this view showing that sIgM plays a distinct and essential role in controlling gut microbiota and metabolic function.

The gut microbiome supports vital physiological functions including digestion metabolite production and immune and neurological regulation. While it is known that sIgA and sIgT (in fish) coat beneficial microbes to help shape microbiota composition and metabolism recent findings indicate that sIgM also coats a substantial portion of gut bacteria in both humans and fish underscoring its significant role in microbiome stability and health.

To investigate the role of sIgM in gut microbiome regulation Dr. Sunyer and his team conducted studies using rainbow trout a teleost fish species whose gut bacteria are coated by sIgM much like in humans. By selectively and temporarily depleting sIgM in these fish the researchers could closely examine its impact. Unlike laboratory mice whose gut microbiota are not coated by sIgM rainbow trout serve as a rare and valuable model for exploring sIgM’s function in maintaining microbiome balance.

The absence of sIgM in the fish gut led to a disruption in microbiome composition known as dysbiosis an imbalance commonly linked to intestinal diseases and impaired physiological functions. This dysbiosis also triggered notable tissue damage and inflammation in the gut driven by the altered microbial landscape.

The absence of gut sIgM revealed its crucial protective role as fish without it showed high mortality in a colitis-like model due to bacteria entering the bloodstream and triggering septic shock. This suggests sIgM helps prevent harmful bacteria from breaching the gut lining. Dr. Sunyer highlighted that systemic IgM may help eliminate escaped microbes via immune mechanisms though further research is needed. The study also found major shifts in gut microbial metabolites without sIgM including a surprising increase in beneficial short-chain fatty acids (SCFAs). These SCFAs vital for gut healing may be produced in response to tissue damage from sIgM loss.

Souirce: https://www.vet.upenn.edu/penn-vet-study-reveals-an-unsung-immune-defender-as-a-key-guardian-of-gut-health-and-metabolism/