Quantitative Analysis of Splenic Natural Killer Cells of Mice Using Imaging Flow Cytometry

Natural killer (NK) cells are crucial innate immune effectors, mediating cytotoxicity against cancer and infected cells through receptors such as NKG2D. Reliable quantification of NK cell subsets is essential for evaluating NK cell-based immune responses in cancer research. Unlike other assays, including traditional flow cytometry used in assessing NK cells, imaging flow cytometry (IFC) is a simple and direct method for quantitative analysis of NK cells. This protocol describes the necessary procedures, including harvesting splenocytes, acquiring these cells labeled with NKG2D antibodies, and analyzing IFC data with IDEAS^® software. We applied this protocol to quantitatively assess the number of splenic NKG2D⁺ NK cells in mice injected with SVTneg2 cancer cells (which carry the p53 G242A missense mutation) and compared them to mice injected with EMT6 cancer cells (which have wild-type p53) or normal fibroblasts. We found that the SVTneg2 cancer cells significantly decreased the number of NKG2D⁺ NK cells in mice by approximately 2-fold (933 cells vs. 2360 cells, p < 0.001) compared with mice injected with EMT6 cancer cells. This IFC protocol can be applied to directly quantify NK cells in vivo. This quantitative protocol allows novices to quickly handle the analysis of cytotoxic NK cells with a single NKG2D marker. Further multicolor flow cytometry and cytokine assay may be required to precisely define the subtypes and effects of NK cells in anticancer immunity. Key features • A simple and direct assay using imaging flow cytometry (IFC) to quantify cytotoxic NKG2D NK cells against breast cancer cells in mice. • Simultaneously collect the flow cytometry characters and each cell image of NK cells and other populations. • Step-by-step identification of interested NK cells mainly relying on image gating (focus, size, morphology). • Highly reliable and applicable to analyze other immune cell subsets or tumor-associated populations with corresponding conjugate antibodies.