INTRODUCTION

Immunological test methods (ITMs) utilize bindings between an antigen (Ag) and antibody (Ab). (See Appendix 1: Abbreviations for a complete list of acronyms used in this chapter.) Enzyme-linked immunosorbent assay (ELISA) is one of the most widely used ITMs for characterization, release, and stability testing of biotechnology products to help ensure the quality of biological drug substances and drug products. The term “ELISA” is used here in a broader sense and includes enzyme immunoassays (EIAs), as well as alternative detection methods, e.g., chemiluminescence and fluorescence.