Cross-Reactivity and Sequence Similarity Between Microbial Transglutaminase and Human Tissue Antigens

Celiac.com 11/26/2025 - Microbial transglutaminase is an enzyme made by bacteria. Food manufacturers commonly use it as a “glue” to bind proteins together in processed foods such as meat, dairy, and baked goods. The study summarized here explored whether this food enzyme might resemble parts of human proteins closely enough to confuse the immune system. If the immune system makes antibodies against microbial transglutaminase, and those antibodies also stick to similar-looking human tissues, this could help explain how exposure to the enzyme might play a role in autoimmune problems.

What the Researchers Wanted to Learn

The team asked two main questions. First, do parts of the microbial transglutaminase protein share meaningful sequence similarity with human proteins that are known targets in autoimmune diseases. Second, do antibodies raised against microbial transglutaminase react with a wide range of human tissues in laboratory testing. Together, these questions address the possibility of “molecular mimicry,” where a foreign protein resembles human tissue closely enough to trigger cross-reactions.

How the Study Was Conducted

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The researchers used two complementary approaches:

• Protein sequence comparison: They compared the amino acid sequence of microbial transglutaminase with many human protein fragments that are linked to autoimmune diseases. A standard bioinformatics tool for local sequence alignment was used to look for stretches where the sequences were highly similar, focusing on segments long enough and identical enough to matter for immune recognition.
• Antibody reactivity experiments: They generated antibodies against microbial transglutaminase in two forms. One was a mixed collection of antibodies from rabbits (called polyclonal), which recognize multiple parts of the target. The other was a single-type antibody from mice (called monoclonal), which binds a specific part of the target. These antibodies were then applied to plates coated with seventy-seven different human tissue antigens from many organ systems. A color-changing plate test measured how strongly the anti–microbial transglutaminase antibodies bound to each human antigen.

Key Findings From the Antibody Experiments

The polyclonal antibody to microbial transglutaminase reacted strongly with seventeen of the seventy-seven human tissue antigens. The most pronounced signals involved mitochondrial antigen M2, antinuclear antibodies, and extractable nuclear antigens, all of which are familiar targets in various autoimmune conditions. The polyclonal antibody also showed significant binding to additional targets, including tissue transglutaminase, thyroid peroxidase, claudins involved in tight junctions, cytoskeletal proteins such as actin, and other components related to immune or structural function.

The monoclonal antibody revealed a narrower pattern, binding significantly to fewer human antigens, which is consistent with its more focused recognition of a single site. Even so, it showed notable reactivity with several targets, including mitochondrial proteins and certain transglutaminase family members. The difference between the broad polyclonal signal and the more selective monoclonal signal is expected and helps confirm that multiple kinds of antibody can identify overlaps between microbial transglutaminase and human tissues.

Key Findings From the Sequence Analysis

From a very large library of human autoimmune-related protein fragments, the researchers identified sixty with meaningful similarity to portions of microbial transglutaminase. Of those, six stood out because they came from human proteins that were both implicated in cross-reactive antibody tests and predicted to bind well to human immune presentation molecules known as human leukocyte antigens. The human proteins involved play essential roles in blood clotting, packaging of DNA, mitochondrial energy production, and cellular signaling.

These six similarity matches connect microbial transglutaminase to human targets associated with a wide range of autoimmune conditions, including rheumatoid arthritis, type 1 diabetes mellitus, primary biliary cholangitis, multiple sclerosis, Sjögren’s syndrome, autoimmune thyroid disease, psoriatic arthritis, ankylosing spondylitis, autoimmune atherosclerosis, and autoimmune uveitis. The common theme is that sequence resemblance exists in places that the immune system is likely to “see,” raising the possibility that antibodies against microbial transglutaminase might also latch onto similar human proteins.

Why These Findings Matter

Transglutaminase enzymes are nature’s “protein cross-linkers.” In the human body, tissue transglutaminase is the main self-protein that becomes the immune target in celiac disease. Microbial transglutaminase, the food additive, can perform similar chemical reactions on proteins in processed foods, including gluten. This can create new complexes that are hard to digest and may be more immunogenic. The study adds two more potential pathways to concern: meaningful sequence similarity between microbial transglutaminase and human proteins, and direct antibody cross-reactivity with many human tissues in a laboratory setting. Together, these findings support the idea that repeated exposure to the food enzyme could contribute to immune confusion in susceptible people.

Interpreting the Results With Care

It is important to recognize what this study does and does not prove. The experiments show that antibodies to microbial transglutaminase can bind to human tissues in a dish, and that sequence similarity exists in regions that might be recognized by the immune system. This supports a plausible mechanism for autoimmune reactions. However, the study does not demonstrate that the enzyme or its cross-linked food complexes circulate through the body in living people or that they directly cause disease. The work is hypothesis-generating and points to the need for clinical studies that measure exposure, immune responses, and outcomes over time.

Potential Implications for Food Processing and the Intestinal Barrier

The authors discuss several ways that microbial transglutaminase might influence health beyond simple sequence mimicry. Cross-linking can make protein structures more resistant to digestion and may alter how food components interact with the intestinal lining. Prior work cited by the authors suggests that microbial transglutaminase can move across the intestinal surface under some conditions, might affect tight junction integrity, and can form complexes with gluten that stimulate immune responses. If these effects occur in real-life settings, they could lower the threshold for immune activation in people who are genetically or environmentally susceptible.

Strengths and Limitations

Strengths include the combination of two independent lines of evidence: computational sequence analysis across a very large set of autoimmune-related human epitopes, and hands-on antibody testing against a broad panel of human tissues. The consistency between these approaches strengthens the central observation that similarity and cross-reactivity exist. Limitations include the absence of direct human exposure measurements, the reliance on in vitro binding rather than patient outcomes, and the focus on a curated set of human antigens rather than the entire human proteome. These boundaries do not diminish the findings but do frame them as an early step toward understanding potential risk.

What This Could Mean for People With Celiac Disease

For individuals with celiac disease, tissue transglutaminase is the self-protein targeted by the immune system, and gluten is the trigger that sets off the response. Microbial transglutaminase is commonly used in food processing and can chemically modify gluten and other proteins. This study suggests three intersecting concerns: the food enzyme can alter gluten in ways that may increase immune recognition; antibodies to the enzyme can bind to many human tissues in the laboratory; and parts of the enzyme resemble human proteins found in autoimmune disease. While this does not prove harm in everyday eating, it highlights a reasonable question: could frequent dietary exposure to the enzyme add to the immune load in some people with celiac disease or in their relatives who are at risk.

The practical takeaway is cautious but clear. People with celiac disease already benefit from minimizing processed foods, reading labels closely, and choosing whole, naturally gluten-free ingredients when possible. Clinicians and researchers may wish to consider microbial transglutaminase exposure when evaluating persistent symptoms or unexplained immune activity despite a gluten-free diet. Future studies that track real-world intake of the enzyme, antibody responses, and clinical outcomes will help determine how significant this factor is and whether guidance should change.

Bottom Line

This study provides evidence that antibodies to microbial transglutaminase can cross-react with many human tissues and that the enzyme shares meaningful sequence similarity with human proteins linked to autoimmune diseases. For the celiac community, these findings point to a potential environmental contributor that deserves further investigation because it may interact with gluten, with the intestinal barrier, and with the very enzyme that defines the disease. The work does not call for alarm, but it offers a thoughtful reason to favor simpler foods, to ask informed questions about processing aids, and to support research that can turn these early signals into clear, practical guidance.

Read more at: pmc.ncbi.nlm.nih.gov