Phosphorylation of tyrosine, serine, and threonine residues is critical for the control of protein activity involved in various cellular events. An assortment of kinases and phosphatases regulate intracellular protein phosphorylation in many different cell signaling pathways. These pathways include T and B cell signaling, regulating growth and cell cycle control, plus cytokine, chemokine, and stress responses. Phosphoflow assays combine phosphoprotein-specific antibodies with the power of flow cytometry to enhance phosphoprotein study. In our assay, peripheral blood mononuclear cells are stimulated by cytokines, fixed, surface-stained with a cocktail of antibodies labeled with MAXPAR (brand name) metal-chelating polymers and permeabilized with methanol. They are then stained with intracellular phospho-specific antibodies.

We use a CyTOF^TM mass cytometer to acquire the ICP-MS (inductively coupled plasma mass spectrometry) data. The current mass window selected is approximately AW 103-203, which includes the lanthanides used for most antibody labeling, as well as iridium and rhodium for DNA intercalators. Subsequent analysis of the dual count signal data using FlowJo software allows for cell types to be analyzed based on the dual count signal in each mass channel. The percentage of each cell type is determined and reported as a percent of the parent cell type. Median values are reported to quantitate the level of phosphorylation of each protein in response to stimulation. Comparing the level of phosphorylation between samples can offer insight to the status of the immune system.