title: Stages of germinal center transit are defined by B cell transcription factor coexpression and relative abundance.
abstract: The transit of T cell-activated B cells through the germinal center (GC) is controlled by sequential activation and repression of key transcription factors, executing the pre- and post-GC B cell program. B cell lymphoma (BCL) 6 and IFN regulatory factor (IRF) 8 are necessary for GC formation and for its molecular activity in Pax5+PU.1+ B cells. IRF4, which is highly expressed in BCL6- GC B cells, is necessary for class switch recombination and the plasma cell differentiation at exit from the GC. In this study, we show at the single-cell level broad coexpression of IRF4 with BCL6, Pax5, IRF8, and PU.1 in pre- and post-GC B cells in human and mouse. IRF4 is down-regulated in BCL6+ human GC founder cells (IgD+CD38+), is absent in GC centroblasts, and is re-expressed in positive regulatory domain 1-positive centrocytes, which are negative for all the B cell transcription factors. Activated (CD30+) and activation-induced cytidine deaminase-positive extrafollicular blasts coexpress Pax5 and IRF4. PU.1-negative plasma cells and CD30+ blasts uniquely display the conformational epitope of IRF4 recognized by the MUM1 Ab, an epitope that is absent from any other IRF4+PU.1+ lymphoid and hemopoietic subsets. Low grade B cell lymphomas, representing the malignant counterpart of pre- and post-GC B cells, accordingly express IRF4. However, a fraction of BCL6+ diffuse large B cell lymphomas express IRF4 bearing the MUM1 epitope, indicative of a posttranscriptional modification of IRF4 not seen in the normal counterpart.
authors.affiliation: Department of Pathology, Columbia University Medical Center, New York, NY 10032, USA. giocatto@gmail.com
authors.forename: Giorgio
authors.initials: G
authors.lastname: Cattoretti
authors.forename: Rita
authors.initials: R
authors.lastname: Shaknovich
authors.forename: Paula M
authors.initials: PM
authors.lastname: Smith
authors.forename: Hans-Martin
authors.initials: HM
authors.lastname: Jäck
authors.forename: Vundavalli V
authors.initials: VV
authors.lastname: Murty
authors.forename: Bachir
authors.initials: B
authors.lastname: Alobeid
mesh_terms: D000818:Animals; D016175:B-Lymphocyte Subsets / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism*; D002465:Cell Movement / Q000235:genetics / Q000276:immunology*; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000172:deficiency / Q000502:physiology; D005434:Flow Cytometry; D018858:Germinal Center / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D050835:Interferon Regulatory Factors / Q000096:biosynthesis* / Q000172:deficiency / Q000502:physiology; D008221:Lymphoid Tissue / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D016393:Lymphoma, B-Cell / Q000737:chemistry / Q000276:immunology / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009928:Organ Specificity / Q000235:genetics / Q000276:immunology; D014066:Palatine Tonsil / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D051560:Proto-Oncogene Proteins c-bcl-6; D014157:Transcription Factors / Q000096:biosynthesis* / Q000172:deficiency / Q000502:physiology; D014407:Tumor Cells, Cultured; D000099218:Interferon Regulatory Factor-4
chemical_list: D004268:DNA-Binding Proteins; D050835:Interferon Regulatory Factors; D051560:Proto-Oncogene Proteins c-bcl-6; D014157:Transcription Factors; D000099218:Interferon Regulatory Factor-4; C490010:Bcl6 protein, mouse