Human germinal center B cells differ from naive and memory B cells by their aggregated MHC class II‐rich compartments lacking HLA‐DO

• Published in: International immunology 2003-04, Vol.15 (4), p.457-466
• Main Authors: Chalouni, Cécile, Banchereau, Jacques, Vogt, Anne B., Pascual, Virginia, Davoust, Jean
• Format: Article
• Language: English
• Subjects: Animals; B-Lymphocyte Subsets - chemistry; B-Lymphocyte Subsets - immunology; CD40 Antigens - metabolism; Cell Compartmentation; Cells, Cultured; germinal center; Germinal Center - immunology; Histocompatibility Antigens Class II - analysis; Histocompatibility Antigens Class II - metabolism; HLA Antigens - metabolism; HLA-D Antigens - analysis; HLA-D Antigens - metabolism; HLA-DR Antigens - metabolism; HLA‐DM; HLA‐DO; HLA‐DR; human B cell subsets; Humans; Immunologic Memory; Mice; Palatine Tonsil - cytology; Palatine Tonsil - immunology
• ISSN: 0953-8178; 1460-2377; 1460-2377
• DOI: 10.1093/intimm/dxg037

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‐κ/λ 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.