6 - The Nature of Antigen-Antibody Interaction

Abstract

This chapter, examines the nature of B cell epitopes, the mechanism by which the antibody recognizes and binds to these epitopes on antigens, and the role of T cell help in B cell activation. The chapter provides an insight into the engagement of the B cell receptor (BCR) on the B cell surface by antigen. It also explores the assays used in the laboratory that are based on these interactions. T-independent (Ti) antigens activate B cells in the absence of major histocompatibility complex (MHC) class II-restricted T cell help. By examining the mechanics of antigen–antibody, a reasonable idea of the interactions that occur on the cell surface between an antigen and an antigen receptor is obtained. In contrast, T-dependent (Td) antigens are proteins of non-repetitive amino acid sequence that bind to mIg but cannot fully activate the antigen-specific B cells on their own. The activation of these B cells cannot occur until the Td antigen is processed and presented by APCs that stimulate T helper cells specific for that antigen. A Td antigen thus contains both B cell and T cell epitopes that facilitate the necessary co-localization of the antigen-specific lymphocytes.