Quantification of natural killer cell polarization and visualization of synaptic granule externalization by imaging flow cytometry

Defining immunological mechanisms underlying NK cell biology is crucial for the treatment and prevention of immune deficiency and malignancy. The limited availability of human biological specimens presents a challenge to the study of human immunobiology. The use of high throughput, multi-parametric assays will not only aid in the definition and diagnosis of complex human immune disorders affecting NK cell function but also advance NK cell biology through population-based assessment of molecular signaling. In an effort to garner the most information from limited numbers of human cells, we designed a quantitative method to study NK cell function using imaging flow cytometry (IFC), which combines multiparametric flow cytometry and fluorescence microscopy. Specifically, we developed IFC as a tool to measure polarization and secretion of lytic granules at the immunological synapse formed between an NK cell and a susceptible target. We have further validated our approach through quantitative comparison with high-resolution confocal microscopy. We show that IFC can be used as a quantitative, high throughput measure of NK cell biological function possessing greater dimensionality than standard flow cytometry.