Investigations of the Secretory Immune System in Human Milk Using Monoclonal Antibodies

Abstract

Secretory IgA (SIgA), the major immunoglobulin in human colostrum and milk, is a complex of glycopeptides. The pathway for the production of these molecules is complicated, since the peptide constituents of each molecule are the products of at least nine different genes and two different cell types. The major portion of the molecule is synthesized by specialized plasma cells which are part of the common mucosal immune system (1) and ultimately home to submucosal sites, including the lactating breast. Formation of an active immunoglobulin product within these plasma cells requires genetic rearrangements, post transcriptional modifications of the messenger RNA’s, and post translational modification and assembly of the nascent peptides. The completed product, polymeric IgA (PIgA) consists of at least four alpha (heavy) chains, four kappa or lambda (light) chains, and a single J or joining chain. These glycopeptide subunits are held together by noncovalent forces as well as interchain disulfide bridges.