Abstract
The physiological importance of cytokines and other factors which control cell and tissue growth and differentiation is widely appreciated. While physiological studies have included the cellular receptors for these factors, studies on their role in disease have concentrated on the measurement of cytokines themselves or soluble receptor components. This reflects in part the technical difficulty of measuring cell surface expression of receptors, which occur at and are functional at very low concentrations. In this review, the potential va lue of surface-expressed receptors as markers of disease is assessed, and methods are described which allow measurements with standard equipment for flow cytometry and tluorescence microscopy.