ELISpot (enzyme-linked immunospot)
In one sentence
ELISpot counts spots formed when sampled cells release a chosen molecule under defined test conditions.
The intuition
Picture a plate that catches small droplets where each cell sits. A cell releasing the molecule being measured leaves a mark. The assay counts those marks; it does not watch the cell kill a tumor. That distinction makes a positive result useful without asking it to answer every question.
How it works
Antibodies on a membrane capture a selected molecule, often interferon gamma, released by nearby cells. After stimulation and incubation, detection reagents make localized spots visible. The laboratory reports spot-forming units relative to the number of cells tested, with the method and background stated.
For antigen testing, cells may receive a candidate peptide or peptide pool. A negative control estimates background; a positive control checks whether the sample can respond. Replicates and predefined criteria help distinguish a response from noise. Viability, prior freezing and sample handling also matter.
A conventional mixed-cell assay does not identify every responding cell. Sorting or additional measurements may be needed to assign a response to a cell type. Spot size and intensity are not a direct meter of tumor killing.
Why it matters in cancer
A vaccine study can compare responses before and after dosing under a consistent protocol. A rise supports increased activity against the test stimulus, within the assay's limits. Human leukocyte antigen (HLA) displays the naturally processed peptide. Artificial peptide addition can bypass the tumor's natural processing and presentation. A response to a peptide therefore needs a separate bridge to recognition of actual tumor cells.
How it is measured
| Field | Interpretation |
|---|---|
| Input | A suitable viable-cell preparation, often blood-derived immune cells |
| Output | Spot-forming units per stated number of input cells, with background handling |
| Controls | Unstimulated or vehicle wells, positive stimulation, replicates and viability |
| Failure modes | High background, dead cells, weak stimulation, merged spots or inconsistent counting |
| Cannot establish alone | The target of each receptor, natural tumor recognition, tissue safety or clinical benefit |
The response cutoff belongs to the specific assay and study. Do not import one paper's positivity rule into a different laboratory report.
Worked example
In a fictional experiment, post-dose cells produce more spots with a candidate peptide than with vehicle. Good controls support a peptide-stimulated response. If the experiment used an expanded culture, that result describes the cultured cells; it is not the direct frequency of responding cells in the original blood draw.
Common confusions
- “More spots” and “more tumor killing” are different observations.
- A negative result can reflect sample or assay limitations rather than no relevant cells anywhere.
- T-cell receptor (TCR) sequencing tracks receptor sequences; its assay concept explains the readout; ELISpot measures secretion after stimulation.
Related concepts
Sources and scope
Source check: October 9, 2026. This page explains a method or mechanism. Expert and learner review remain pending.
- Peptide-specific interferon-gamma ELISpot protocol.
- IFN-gamma ELISpot protocol and interpretation in vaccine research.
- Primary assay-validation study in nonhuman primates — method validation does not establish cancer efficacy.