Rare Cell Populations Overwhelmed by Abundant Cells (Flow Cytometry (Sample Considerations))

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Target rare immune cell populations (e.g., dendritic cells, innate lymphoid cells, hematopoietic progenitors) cannot be adequately resolved or quantified due to overwhelming signals from abundant terminally differentiated cells in lymphoid tissues or non-lymphoid tissues. Common causes: 1) Immune cells underrepresented in non-lymphoid tissues (brain, lung, liver, tumor) without leukocyte-specific gating markers like CD45 2) Rare subsets in lymphoid tissues (bone marrow, spleen) masked by abundant terminally differentiated cells expressing Ter119, CD3, CD19, B220, CD11b, CD11c 3) Multicolor panel lacks lineage exclusion markers to suppress signals from non-target populations 4) Histogram-based gating captures outliers (CD11c-int MHCII+/-) instead of true double-positive populations, inflating percentages (e.g., 4.5% vs actual 1.2%) Solutions: 1) Include CD45 (leukocyte common antigen) in panels for non-lymphoid tissues to distinguish white blood cells from tissue resident cells 2) Add lineage cocktails (mouse: CD3, GR1, CD11b, B220, Ter119; human: CD3, CD14, CD19, CD20, CD56) to a single dump channel to gate out differentiated cells 3) Use bivariate plots (dot plot or pseudocolor plot) with two markers (e.g., CD11c and MHC Class II) instead of single-parameter histograms to accurately gate rare populations 4) Employ commercial lineage cocktails (BioLegend mouse/human Lineage Cocktails) to minimize fluorophore usage while excluding multiple lineages