40] Use of protein A in the detection and quantitation of immunoglobulin G on the surface of lymphocytes

Abstract

This chapter reviews that cell-associated IgG molecules either produced by, or attached to, lymphoid cells can be detected and quantitated using labeled protein A (SpA). There are two main methods for detection and/or quantitation of surface IgG: (1) cytochemical methods using SpA labeled with fluorescent dyes detected by fluorescent microscopy; radionuclides detected by autoradiography; electron-dense materials detected by electron microscopy, or microparticles detected by light, fluorescent, or scanning microscopy, and (2) radiochemical methods using SpA labeled with 125I, 131I or 3H, followed by determination of radioactivity in a gamma or scintillation counter. The chapter also discusses the labeled SpA preparations that exhibit three main features: (1) the ability to react with IgG, (2) low content of free, unbound tracer, and (3) low nonspecific binding to the cell surface. It reviews that the last property of labeled SpA preparations can be easily checked by omitting treatment of cells with the specific antibody when antigenic markers are tested.