How many cells per well should I use in ELISpot?
The number of cells in each well must be adjusted to the cell type and the expected frequency of the secreting cells. If the frequency is very low, e.g. 1 in 10,000 cells, a higher number of cells is needed, often around 250,000 cells/well. When the frequency of secreting cells is high, e.g 1 in 10 cells, around 5,000 cells/well are sufficient. Cell numbers do not always show linearity in the assays due to the need for optimal cell-to-cell contact with e.g. antigen-presenting cells for sufficient stimulation. When analyzing antigen-specific T-cells, PBMC should not be below 200,000 cells per well.
We generally do not recommend to use more than 500,000 cells/well since this may create multiple cell layers which, in turn, can result in reduced spot quality due to the increased distance between cells and the ELISpot membrane.