Results from the first gating proficiency panel of intracellular cytokine staining (ICS) highlighted the value of using a consensus gating approach to reduce the variability across laboratories in reported %CD8+ or %CD4+ cytokine-positive cells. Based on the data analysis from the first proficiency panel, harmonization guidelines for a consensus gating protocol were proposed. To validate the recommendations from the first panel and to examine factors that were not included in the first panel, a second ICS gating proficiency panel was organized. All participants analyzed the same set of Flow Cytometry Standard (FCS) files using their own gating protocol. An optional learning module was provided to demonstrate how to apply the previously established gating recommendations and harmonization guidelines to actual ICS data files. Eighty-three participants took part in this proficiency panel. The results from this proficiency panel confirmed the harmonization guidelines from the first panel. These recommendations addressed the (1) placement of the cytokine-positive gate, (2) identification of CD4+ CD8+ double-positive T cells, (3) placement of lymphocyte gate, (4) inclusion of dim cells, (5) gate uniformity, and (6) proper adjustment of the biexponential scaling. In addition, based on the results of this proficiency gating panel, two new recommendations were added to expand the harmonization guidelines: (1) inclusion of dump channel marker to gate all live and dump negative cells and (2) backgating to confirm the correct placement of gates across all populations. © 2020 International Society for Advancement of Cytometry.

\"Gating\" refers to the selection of successive subpopulations of cells for analysis in flow cytometry. It is usually performed manually, based on expert knowledge of cell characteristics. However, there can be considerable disagreement in how gates should be applied, even between individuals experienced in the field. While clinical software often automates gating, and some guidelines do exist (especially for clinical assays), there are no comprehensive guidelines across the various types of immunological assays performed using flow cytometry. Here we attempt to provide such guidelines, focused on the most general and pervasive types of gates, why they are important, and what recommendations can be made regarding their use. We do so through the display of example data, collected by academic, government, and industry representatives. These guidelines should be of value to both novice and experienced flow cytometrists analyzing a wide variety of immunological assays.