What Is A Teer Assay Measuring Barrier Integrity?

A TEER assay measures how well a layer of cells blocks the flow of electrical current. TEER stands for transepithelial electrical resistance. It is a direct, real-time way to assess the strength of a biological barrier, such as the lining of the gut, the lungs, or the blood-brain barrier.

The test works by placing electrodes on either side of a cell layer grown in a lab. A small electrical current is passed through the cells, and the resistance to that current is measured. If the cells form a tight, healthy barrier, the resistance is high. If the barrier is damaged or leaky, the resistance drops.

This measurement is a standard tool in medical research. It is used to study diseases involving barrier breakdown, test drug toxicity, and evaluate treatments designed to protect or repair tissue barriers.

How Does a TEER Assay Actually Work?

A TEER assay requires a specific setup called a Transwell system. Researchers grow cells on a porous membrane inside a small insert. This insert sits in a well, creating two separate compartments. The top compartment represents one side of the barrier, and the bottom compartment represents the other.

To measure, a researcher places one electrode in the top compartment and one in the bottom. The device sends a small alternating current across the cell layer. The resistance is recorded in ohms, then multiplied by the surface area of the membrane to give a standard value: Ω·cm².

The current used is very small and alternating, not direct. This matters because direct current can damage cells. Alternating current passes through without harming the living tissue.

The entire process takes seconds. It does not destroy the cells, so the same sample can be measured repeatedly over days or weeks. That makes it ideal for tracking how a barrier changes over time.

What Is a TEER Assay Measuring Barrier Integrity In Practical Terms?

TEER is measuring the physical tightness of the junctions between cells. Cells in a barrier tissue are connected by protein structures called tight junctions. These junctions seal the space between neighboring cells, controlling what passes through the tissue.

When tight junctions are intact, ions and other charged particles cannot easily cross. This creates high electrical resistance. When tight junctions break down, ions pass freely, and resistance falls.

So a TEER reading is essentially a proxy for tight junction health. It does not tell you which specific protein is damaged, and it does not tell you why the barrier is leaky. But it tells you clearly that a leak exists and how severe it is.

This is why TEER is so widely used. It gives a quick, reliable snapshot of barrier function without requiring complex analysis.

What Are the Common Applications of TEER Assays?

TEER assays are used across many fields of biomedical research. The most common applications include:

• Gut barrier research: Studying conditions like inflammatory bowel disease or celiac disease, where intestinal permeability increases.
• Drug development: Testing whether a drug damages the intestinal lining or the blood-brain barrier.
• Toxicology screening: Checking whether chemicals or food additives disrupt barrier function.
• Nanoparticle research: Evaluating how tiny particles cross biological barriers.
• Disease modeling: Growing diseased cells in the lab and comparing their barrier function to healthy cells.

In each case, the TEER value is the primary readout. A researcher might expose cells to a toxin and watch the resistance drop over hours. Or they might test a protective compound and see whether it prevents that drop.

The assay is also common in cancer research. Tumor cells often have weaker barriers than healthy cells, and TEER can quantify that difference.

What Are the Limitations of TEER Assays?

TEER is a powerful tool, but it has real limitations. The most important is that it measures only the passage of charged particles. Uncharged molecules, like glucose or certain drugs, can cross a barrier without affecting the TEER reading.

This means a high TEER value does not guarantee the barrier is completely intact. It only confirms that ionic movement is restricted. For a full picture, researchers often combine TEER with other tests, such as measuring the passage of fluorescent tracer molecules.

Another limitation is that TEER values vary widely between cell types and lab conditions. A “normal” value for one cell line may be abnormal for another. There is no universal cutoff that indicates a healthy barrier.

Temperature also affects readings. Cells must be kept at a consistent temperature, usually 37°C, because resistance changes with temperature. Small variations can skew results.

Electrode placement matters too. If the electrodes are not positioned consistently between measurements, the values will not be comparable.

How Do Researchers Interpret TEER Values?

Interpretation depends entirely on the experimental context. Researchers typically establish a baseline reading for their specific cell culture system, then compare all subsequent measurements against that baseline.

For example, a researcher studying intestinal cells might record a baseline of 200 Ω·cm². If they add a compound that reduces the reading to 50 Ω·cm², that indicates severe barrier disruption. If the reading stays near 200, the barrier is intact.

Some cell types naturally produce higher resistance than others. Kidney cells and certain intestinal lines often produce very high readings, sometimes over 1000 Ω·cm². Other cell types, like some lung lines, produce much lower readings.

The direction of change matters more than the absolute number in most studies. A consistent drop in resistance over time is a clear sign of barrier breakdown.

What Is the Difference Between TEER and Permeability Assays?

TEER measures electrical resistance. Permeability assays measure the actual passage of molecules. They answer related but distinct questions.

TEER tells you about the barrier to ions. Permeability assays tell you about the barrier to specific molecules, such as fluorescent dyes, proteins, or drugs. A researcher might use both in the same experiment.

For example, a study might show a drop in TEER and an increase in fluorescent dye passage. Together, these findings confirm that the barrier is compromised. Using only one method leaves gaps in the picture.

Permeability assays take longer, usually hours, because molecules must physically cross the cell layer. TEER is nearly instantaneous. This speed is why TEER is often used for time-course experiments.

What Are the Best Practices for Getting Reliable TEER Measurements?

Reproducibility is the biggest challenge in TEER assays. Small changes in technique can produce large changes in readings. Several practices improve reliability.

First, allow cells to form a stable monolayer before measuring. Measuring too early gives artificially low readings. Most cell types need several days to develop mature tight junctions.

Second, keep the culture medium fresh. Old medium changes the ionic composition and can alter readings. Replacing the medium before measurement is standard practice.

Third, use the same electrodes for all measurements in a study. Different electrodes can give slightly different readings. Calibrating electrodes regularly also helps.

Fourth, record temperature. Most published protocols specify that measurements are taken at 37°C. If the plate has been out of the incubator for a few minutes, readings will drift.

Finally, take multiple readings per well. Cell layers are not perfectly uniform, and a single reading may not represent the whole surface. Averaging several readings gives a more accurate value.