How a Single Immune Protein Works Two Different Ways to Protect Against Type 1 Diabetes

Scientists have known for years that our immune system includes specialized cells called regulatory T cells that act as a brake on autoimmunity. A protein called CD137 sits on the surface of many of these protective cells. What researchers recently discovered is that CD137 has a hidden complexity: through a molecular process called alternative splicing, the same gene can produce two versions—one that stays attached to the cell surface and one that floats free in the bloodstream. Until now, scientists didn't fully understand what each form actually does.

To understand the role of CD137, researchers used NOD mice, an animal model that naturally develops Type 1 diabetes in ways similar to humans. They specifically removed CD137 from the regulatory T cells of these mice. The result was clear: without CD137, the mice developed Type 1 diabetes much faster than normal.

The acceleration wasn't subtle. When CD137 was absent, immune cells called effector T cells expanded dramatically and invaded the pancreatic islets—the insulin-producing regions under attack in Type 1 diabetes. The regulatory T cells themselves also became less effective, showing fewer signs of their characteristic protective activity and appearing less frequently in the pancreas where they were needed most.

The researchers then performed a more nuanced experiment. They restored only the soluble form of CD137—the floating version—in regulatory T cells that lacked both forms. Even without the membrane-bound CD137, restoring the soluble version alone reduced immune activation in the pancreatic islets and slowed diabetes development.

This finding was striking because it showed that the two forms of CD137 don't simply duplicate each other's work. Instead, they appear to operate through separate mechanisms, each contributing independently to holding back autoimmune diabetes. The soluble form seems to act directly on the activated immune cells within the islets, while the membrane form may work through different cellular interactions.

This study adds a layer of detail to our understanding of how the immune system's natural brakes work. Regulatory T cells are one of the body's strongest defenses against Type 1 diabetes, and CD137 appears to be an important part of how these cells function. By identifying that both forms of CD137 are needed, researchers have pinpointed a potential vulnerability in this system—when CD137 expression goes wrong, diabetes can accelerate.

These findings open new questions: Could therapies that boost CD137 expression or activity help strengthen the body's natural regulatory T cells? Would strategies that enhance either the soluble or membrane form be most effective? The answers will require further research, but this work suggests that CD137 is a promising target for understanding and potentially treating Type 1 diabetes.

Source: The Journal of experimental medicine. Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.