Human germinal center B cells differ from naive and memory B cells by their aggregated MHC class II-rich compartments lacking HLA-DO.
To generate memory B cells bearing high-affinity antibodies, naive B cells first encounter antigen in the T cell-rich areas of secondary lymphoid organs. There, they are activated by antigen-specific T cells and become germinal center (GC) founder B cells. GC founders enter the GC to become centroblasts that proliferate and mutate their BCR. Centroblasts differentiate into centrocytes that undergo selection, which requires both the recognition/capture of antigen on follicular dendritic cells and the presentation of processed antigen to GC T cells. Because at each stage of differentiation B cells act as antigen-presenting cells, we analyzed their content of HLA-DR(+)-rich compartments (MIIC), as well as their expression of HLA-DM, which catalyzes peptide loading of class II molecules, and HLA-DO, which interacts with HLA-DM and focuses MHC class II peptide loading on antigens internalized by the BCR. Naive and memory B cells concentrate HLA-DR, -DM and -DO into compartments dispersed under the cell surface, which are identified by their expression of lysosome-associated membrane protein (Lamp)-1 as late endosomes/lysosomes. GC founders and GC B cells express larger Lamp-1(+)DR(+) compartments that are concentrated in the juxta-nuclear region. These compartments express lower levels of HLA-DM and virtually no HLA-DO. Upon induction of a GC founder phenotype through the prolonged (days) co-ligation of BCR and CD40, the naive B cell's peripheral DR(+)DM(+)Lamp-1(+) compartments aggregate in a polar fashion close to the nucleus. Furthermore, HLA-DO expression virtually disappears, whereas low levels of HLA-DM remain co-localized with HLA-DR. Anti-kappa/lambda antibodies, used as surrogate antigens, are promptly (minutes) endocytosed in naive, memory and GC B cells. Then, naive and memory B cells target the surrogate antigen to their peripheral HLA-DO(+) MIIC, while GC B cells target it to their HLA-DO(-) MIIC aggregates. Taken together, our results show that human GC B cells differ from naive and memory B cells by their aggregated MIIC that lack HLA-DO.
Chalouni
Cécile
C
Baylor Institute for Immunology Research, Dallas, TX 75204, USA.
Banchereau
Jacques
J
Vogt
Anne B
AB
Pascual
Virginia
V
Davoust
Jean
J
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000737:chemistry / Q000276:immunology*; D019013:CD40 Antigens / Q000378:metabolism; D002451:Cell Compartmentation; D002478:Cells, Cultured; D018858:Germinal Center / Q000276:immunology*; D006680:HLA Antigens / Q000378:metabolism; D006681:HLA-D Antigens / Q000032:analysis / Q000378:metabolism*; D006684:HLA-DR Antigens / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D007156:Immunologic Memory; D051379:Mice; D014066:Palatine Tonsil / Q000166:cytology / Q000276:immunology
D019013:CD40 Antigens; D006680:HLA Antigens; D006681:HLA-D Antigens; C084245:HLA-DM antigens; C046148:HLA-DO antigens; D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II