Processing of Immunoglobulin-associated Antigen in B Lymphocytes

For most antigens presented in association with class II major histocompatibility complex (MHC) molecules, an intracellular processing step is required to produce a suitable ligand for binding to the class II MHC glycoproteins and, as a complex, to the T-cell receptor. The available evidence strongly suggests that following endocytosis, processing and unfolding take place in intracellular compartments and that suitable MHC/peptide complexes are then returned to the cell surface. Using T cells to assay for the appearance of processed determinants, it has been established that these antigen-processing events take approximately 1 hour and are sensitive to chloroquine and fixation of the antigen-presenting cells (APCs) and to inhibitors of endosomal/lysosomal proteinases (Ziegler and Unanue 1982; Lanzavecchia 1985; Buus and Werdelin 1986).