Blood Test Could Detect Infection Exposure History

This makes it difficult to understand a person’s full infection history or immune protection using a simple test. Because immune responses vary widely between individuals, this diagnostic potential remains largely untapped. Researchers are now working toward a blood-based approach that could reconstruct lifelong exposure to infections by reading immune cell signatures.

T-cells detect infections through highly specific surface sensors known as T-cell receptors, each designed to bind a particular antigen. When a matching antigen is encountered, the corresponding T-cells multiply rapidly. While most die after clearing the infection, a subset remains as memory T-cells, preserving a record of that encounter. Researchers at the University of Erlangen-Nuremberg (FAU, Erlangen, Germany), in collaboration with the University Hospital Erlangen (Erlangen, Germany), have shown that exposure to a pathogen leads to the expansion of many T-cell clones, creating detectable patterns in the blood.

Although individual T-cell receptors differ greatly between people, infections often generate shared or even identical receptor sequences across multiple individuals. These recurring patterns form what researchers describe as an immunological fingerprint. By comparing T-cell receptor sequences from individuals with confirmed past infections, the team aims to identify receptor features specific to particular pathogens. Machine learning algorithms will be used to analyze these large datasets and link receptor patterns to known infectious diseases.

The researchers are initially focusing on viruses that can cause complications during pregnancy, such as rubella. One goal is to assess whether vaccinated or previously infected individuals, including pregnant women, still retain protective immunity by analyzing their T-cell profiles. This approach could complement or even extend beyond traditional antibody-based serological tests. In the long term, the team plans to build libraries of pathogen-specific T-cell receptors and contribute to a global database. This could allow a single blood test to provide a comprehensive overview of an individual’s infection history and immune status across their lifetime.

“Each infection leaves a trace in the immune system. For example, if you have ever had the flu, you will have more T-cells whose receptors match the flu virus antigens than someone who has not.” said Professor Kilian Schober, PhD, lead investigator. “In future, a single test may be sufficient to illustrate an individual’s infection history over their entire lifetime.”

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University Hospital Erlangen