Immune responses at mucosal surfaces play a major role in host mucosal defense against microbial pathogens and in the pathogenesis of acute and chronic mucosal inflammatory diseases. This volume draws on a broad spectrum of molecular biologic, biochemical, and immunogenetic approaches in combination with human and murine in vitro cell culture and in vivo model systems to address questions in mucosal immunity. Humans produce more immunoglobulin A (IgA) than all other antibody isotypes combined, most of which is rapidly transported into the external secretions bathing mucous membranes. It has been estimated that more than 3 grams of IgA are transported daily into mucosal secretions, carrying out a wide range of antimicrobial and anti-inflammatory functions. IgA is the second most abundant class of antibody in the bloodstream, contributing to systemic as well as secretory immunity. Recent advances in human genomics, gene regulation, structural biology, cell signaling, and immunobiology have greatly enhanced our understanding of this important class of antibody. This book is designed to serve as a concise reference of the present knowledge of the biology of IgA, including structure of IgA and its interaction with Fc receptors; epithelial transport of IgA; regulation of the mucosal IgA system; biological roles of IgA, including newly discovered functions; IgA-associated diseases, and therapeutic applications for IgA. Chapters have been contributed by internationally recognized leaders in the field of IgA research, representing 8 countries on 3 continents.