Optimization of stimulation and staining conditions for intracellular cytokine staining (ICS) for determination of cytokine-producing T cells and monocytes

Cell-mediated responses to immunological stimuli are often localised in inflammatory sites and involve a number of cell types. These responses can be functionally characterised at the single-cell level on the basis of the types of cytokines expressed either in whole blood or PBMCs. The ability to measure antigen-specific cell responses at the single cell level is an important tool with a wide range of potential applications ranging from studies of disease pathogenesis to the evaluation of vaccines.

A number of experiments were performed in this study in order to establish the optimal conditions for in vitro stimulation of cytokine production by T cells and monocytes in whole blood samples collected from healthy adult Malawian participants and the optimal staining conditions for various cytokine producing cells. Different stimulation methods and conditions, different culture tubes and incubators and different antibody labelling conditions were assessed in order to establish optimal conditions for detecting cytokine-producing cells in whole blood samples.

The use of PMA plus Ionomycin produced highest cytokine-producing T cells whereas LPS was a better stimulant for cytokine producing monocytes. Stimulation of whole blood for 5 h was optimal for cytokine detection in T cells whereas 4 h was optimal for monocytes. BFA was found to be a better Golgi blocker than Monensin and the use of 15 ml Falcon-type polypropylene tubes while stationary resulted in the detection of the highest proportion of cytokine-producing cells. T cells were found to be producers of mainly TNF-α, IFN-γ and IL-2 whereas Monocytes were mainly producing TNF-α and IL-6. Anti-CD3-PerCP (used at a ratio of 1:25), anti-CD14-APC (used at a ratio of 1:50) and anti-cytokine-PE (used at a ratio of 1:12.5) resulted in the best results. The highest cytokine production monocytes were detected when 1 X FACS Lysing solution was used at a volume of 40X that of the whole blood sample compared to the other volumes. These optimal conditions are essential in determination of proportion of cytokine-producing cells using ICS in whole blood.