title: Delivery of B cell receptor-internalized antigen to endosomes and class II vesicles.
abstract: B cell receptor (BCR)-mediated antigen processing is a mechanism that allows class II-restricted presentation of specific antigen by B cells at relatively low antigen concentrations. Although BCR-mediated antigen processing and class II peptide loading may occur within one or more endocytic compartments, the functions of these compartments and their relationships to endosomes and lysosomes remain uncertain. In murine B cells, at least one population of class II- containing endocytic vesicles (i.e., CIIV) has been identified and demonstrated to be distinct both physically and functionally from endosomes and lysosomes. We now demonstrate the delivery of BCR-internalized antigen to CIIV within the time frame during which BCR-mediated antigen processing and formation of peptide-class II complexes occurs. Only a fraction of the BCR-internalized antigen was delivered to CIIV, with the majority of internalized antigen being delivered to lysosomes that are largely class II negative. The extensive colocalization of BCR-internalized antigen and newly synthesized class II molecules in CIIV suggests that CIIV may represent a specialized subcellular compartment for BCR-mediated antigen processing. Additionally, we have identified a putative CIIV-marker protein, immunologically related to the Igalpha subunit of the BCR, which further illustrates the unique nature of these endocytic vesicles.
authors.affiliation: Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8002, USA. jdrake@northnet.org
authors.forename: J R
authors.initials: JR
authors.lastname: Drake
authors.forename: P
authors.initials: P
authors.lastname: Webster
authors.forename: J C
authors.initials: JC
authors.lastname: Cambier
authors.forename: I
authors.initials: I
authors.lastname: Mellman
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D015703:Antigens, CD / Q000032:analysis; D015415:Biomarkers / Q000032:analysis; D051925:CD79 Antigens; D002451:Cell Compartmentation / Q000276:immunology; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D011992:Endosomes / Q000276:immunology* / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D051379:Mice; D011947:Receptors, Antigen, B-Cell / Q000032:analysis / Q000378:metabolism*; D013347:Subcellular Fractions / Q000276:immunology / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D015415:Biomarkers; D051925:CD79 Antigens; C497881:CD79A protein, human; C497882:Cd79a protein, mouse; D000949:Histocompatibility Antigens Class II; D011947:Receptors, Antigen, B-Cell