The ELISPOT (or ELISA Spot) assay is a remarkably sensitive tool for detecting antibodies, granzymes or cytokines secreted by cells in culture, and for enumarting the number of cells that secrete these substances. It requires incubating the cells in question within a well, so that they secrete the substances in question.  These substances bind to capture antibodies coating the well bottom.  The cells are then removed, after which enzyme-labeled detection antibodies and a chromogenic substrate for the enzyme are applied, allowing the bound substances to be graphically detected.

Also see: Immunogenic