Flow cytometry as a tool for measurement of steroid hormone receptor protein expression in leukocytes

Measurement of protein expression in live, intact cells using flow cytometry (FC) has been employed for several decades in the areas of immunology, cell biology, and molecular biology. More recently, this technique has found appreciation in applied scientific fields, including cancer biology and endocrinology, to serve as a tool for identifying cells more likely to respond to specific treatments. FC, also referred to as fluorescence-activated cell sorting (FACS), is an antibody-based method that provides the user with an ability to identify proteins expressed on surfaces of cells as well as in the cytoplasm, including steroid hormone receptors. This technique is most useful for examining specific cell types in a heterogeneous population and therefore can be used to identify cells more likely to respond to treatments based on expression of the appropriate receptor. Isolation of purified subpopulations for further manipulation and investigation of functional capacity is also possible using a cell sorter, which uses similar technology to isolate cells for use by the researcher. This is especially important for studying responses of less abundant cell populations in tissues that express high levels of a target protein or receptor of interest. Furthermore, FACS analysis is clinically useful to identify and isolate responsive cell populations, which may be less appreciable in whole tissues because of the diluting effects of surrounding, nonresponding cell types. Immune cells are commonly utilized as a source of cell populations in the FC technique and have previously been shown to express steroid hormone receptors and respond to steroid hormone treatment. Here, we demonstrate that FC is a useful tool for identifying immune cells expressing steroid hormone receptor protein. This method can also be easily expanded to include other, nonimmune cell populations to address specific research questions related to steroid hormone receptor biology.