The capture antibody creates a local measurement zone around each secreting cell. As the selected cytokine, antibody, or other molecule is released, it binds near its source rather than becoming represented only as a pooled well signal. Subsequent detection and enzyme-mediated color development convert these localized events into countable spots, linking each spot to a responding cell.
Choosing the secreted analyte determines which immune function the assay reports. A cytokine readout can indicate antigen-stimulated cellular activity, whereas an antibody readout addresses antibody-secreting cells; other secreted molecules can be selected for different questions. This flexibility allows the same general platform to examine distinct components of an immune response without treating all secretion as equivalent.
Unlike a bulk assay that summarizes material from many cells, ELISpot preserves information about responding-cell frequency. That distinction matters when only a small fraction of cells reacts to an antigen or infectious-agent stimulus. Counting spots can therefore reveal rare antigen-specific T- or B-cell activity that an averaged measurement may fail to show.
A basic workflow begins with cells placed in wells coated with a capture antibody and exposed to the selected stimulus. During the assay, released analyte is retained near producing cells. Detection antibodies then identify the captured material, and an enzyme-mediated color reaction generates spots for counting. The resulting count measures secreting-cell activity under the chosen stimulation condition.
In vaccine research, ELISpot can assess antigen-specific immune activity after exposure to a vaccine-related stimulus. The assay is also useful for monitoring host immunity and characterizing responses to infectious agents. Because it reports responding cells rather than only a pooled signal, investigators can determine whether a functional response is present and how many cells contribute to it.
Within immunology and infection studies, the assay can be configured around either T-cell or B-cell activity by selecting an appropriate stimulation and secreted target. This makes it useful for examining different aspects of cellular and antibody-related responses to antigens or infectious agents. The output is especially informative when the biologically important population is uncommon among the tested cells.