A cross-campus team of McMaster University researchers has identified why some patients develop dangerous blood clots after exposure to a common blood thinner – and a potential way to prevent it.

The study, published on Sept. 11 in Nature Communications, combines the university’s expertise from chemistry, structural biology and transfusion medicine to reveal how a normally harmless protein in the blood can become the target of harmful antibodies, a discovery that could pave the way for improved diagnostic tests and future therapies.

The research focused on platelet factor 4 (PF4), a protein naturally produced by the body that plays a role in blood clotting. In some patients receiving the commonly used blood thinner heparin, PF4 can change shape and become the target of antibodies that trigger a rare but potentially life-threatening immune reaction called heparin-induced thrombocytopenia (HIT).

Although uncommon, HIT can cause dangerous blood clots that may lead to stroke, heart attack, limb loss or even death if not identified and treated promptly.

The findings are the result of a highly interdisciplinary collaboration that brought together researchers from multiple faculties and departments across McMaster.

The work was led by Giuseppe Melacini of the departments of Chemistry and Chemical Biology and Biochemistry and Biomedical Sciences; Ishac Nazy of the Michael G. DeGroote Centre for Transfusion Research and the departments of Medicine and Biochemistry and Biomedical Sciences; and Qiulin Ma, a postdoctoral candidate in Melacini’s lab.

“This study provides a molecular explanation for how PF4 becomes a pathogenic antigen,” said Melacini. “By identifying the structural switch that controls this process, we’ve revealed a new way of thinking about how to detect or prevent these dangerous immune reactions.”

Using advanced nuclear magnetic resonance (NMR) spectroscopy, the researchers identified a previously unknown “molecular switch” within PF4 that controls whether the protein stays in a closed, harmless shape or opens into a shape that can be recognized by harmful antibodies.

When PF4 opens — particularly when it interacts with the blood thinner heparin — it can become a target for the immune system and trigger HIT, which can cause life-threatening blood clots.

The team demonstrated that altering this switch can keep PF4 in its closed form, dramatically reducing its ability to provoke an immune response.

The Melacini team provided the necessary expertise in biophysics and NMR spectroscopy and developed key methods to identify the switch controlling PF4 antigenicity, while Nazy and colleagues contributed deep clinical and translational expertise in blood disorders, platelet biology and immune-mediated clotting diseases.

Together, the team bridged the gap between atomic-level protein structure and real-world clinical challenges faced by patients and physicians.

“This work shows the power of collaboration across disciplines,” said Nazy. “By combining advanced molecular imaging approaches with clinical expertise, we were able to answer a longstanding question about what causes PF4 to become a target of harmful antibodies.”

Beyond advancing the understanding of HIT, the discovery could have important practical implications. Melacini also added that the newly identified switch, together with access to state-of-the-art NMR facilities, may provide a foundation for developing more precise diagnostic tests that identify pathogenic antibodies earlier and more accurately.

Earlier detection could help clinicians intervene sooner, improving patient outcomes while reducing complications and healthcare costs.

The researchers say the work also serves as a proof of concept for studying complex protein dynamics using NMR spectroscopy, offering a roadmap for investigating other diseases driven by subtle, yet functionally critical, structural changes in proteins.

The study was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and supported by the China Scholarship Council (CSC).