Few or no spots are visible after development, or spots are extremely faint and difficult to detect even though cytokine-secreting cells should be present.
Common Causes
1Cells not incubated long enough or insufficient time to respond to stimulant
2Cells not stimulated correctly or inappropriate stimulation conditions
3Inadequate color development due to improper reagent storage or loss of activity
4Insufficient cells per well (below optimal 1-2 × 10⁵ cells range)
5Primary or secondary antibody concentration too low
Solutions
1Increase cell incubation time or use indirect method (pre-treat cells with stimulant)
2Use positive stimulation control with known inducer of target cytokine/protein
3Monitor color development with overhead microscope; verify reagent storage and activity
4Increase cell number to 1-2 × 10⁵ cells per well; optimize as needed
5Increase primary and/or secondary antibody concentrations through optimization