The Use of Flow Cytometry to Detect Intracellular Cytokine Production in Individual Cells

The current methods commonly employed to detect cytokine production have several drawbacks. Bioassays are not necessarily cytokine-specific in that they measure functional properties. The production of supernatant cytokine protein can be readily measured by enzyme-linked immunosorbent assay (ELISA) methods, but unless a highly purified cell population was cultured, this method does not identify the population of cells responsible for the cytokine production. In addition, the results of ELISA assays reflect the net outcome of produced, absorbed and degraded cytokine and do not distinguish between biologically active and inactive substances. The detection of cytokine RNA (in-situ hybridization and reverse transcriptase-polymerase chain reaction) adequately detect gene expression, but this does not guarantee the translation of the message into cytokine protein. Thus, methods were developed to detect cytokine production at the individual cell level. These methods usually also possessed the ability to positively identify the cell population of interest. The various strategies that have been utilized have been reviewed by Lewis (1 ).