title: Naive B lymphocytes undergo homeostatic proliferation in response to B cell deficit.
abstract: Naive peripheral B cells are maintained in sufficient numbers and diversity to mount effective immune responses against infectious agents. However, the size and repertoire of this B cell pool is constantly diminished by normal cell turnover and Ag activation. Homeostatic (Ag-independent) proliferation in response to B cell depletion is one mechanism to compensate for this cell loss. We have used purified CFSE-labeled B cells and an adoptive transfer model system to show that immature and mature B cells divide in a variety of B cell-deficient (scid, xid, IL-7(-/-), and sublethally irradiated) hosts. Homeostatic B cell proliferation is T cell independent, and B cells that have replicated by this mechanism retain the antigenic phenotype of naive B cells. Replication is significantly reduced in B cell-sufficient normal or B cell-reconstituted immunodeficient recipients by the action of competing mature follicular B cells. Using xid mice and transcription factor knockouts, we show that the activation signal(s) that lead to homeostatic B cell proliferation require Bruton's tyrosine kinase; however, c-Rel, a Bruton's tyrosine kinase-induced NF-kappaB/Rel transcription factor critical for Ag and mitogen stimulation, is dispensable, indicating the uniqueness of this activation pathway. Survival and replication signals can also be separated, because the transcription factor p50 (NF-kappaB1), which is required for the survival of peripheral B cells, is not necessary for homeostatic replication. Homeostatic B cell proliferation provides an Ag-independent mechanism for the maintenance and expansion of naive B cells selected into the mature B cell pool.
authors.affiliation: Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Cabatingan
authors.forename: Madelyn R
authors.initials: MR
authors.lastname: Schmidt
authors.forename: Ranjan
authors.initials: R
authors.lastname: Sen
authors.forename: Robert T
authors.initials: RT
authors.lastname: Woodland
mesh_terms: D019264:Adoptive Transfer; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology* / Q000276:immunology* / Q000473:pathology / Q000637:transplantation; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D002455:Cell Division / Q000235:genetics / Q000276:immunology; D005246:Feedback; D005260:Female; D006706:Homeostasis / Q000235:genetics / Q000276:immunology*; D016130:Immunophenotyping; D020381:Interleukin-17 / Q000172:deficiency / Q000235:genetics; D007399:Interphase / Q000235:genetics / Q000276:immunology*; D008231:Lymphopenia / Q000235:genetics / Q000276:immunology*; D008297:Male; D051379:Mice; D008805:Mice, Inbred A; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D016513:Mice, SCID; D008822:Mice, Transgenic; D016328:NF-kappa B / Q000172:deficiency / Q000235:genetics; D052002:NF-kappa B p50 Subunit; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D020569:Proto-Oncogene Proteins c-rel / Q000172:deficiency / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013154:Spleen / Q000166:cytology / Q000276:immunology / Q000473:pathology
chemical_list: D020381:Interleukin-17; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D020569:Proto-Oncogene Proteins c-rel; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625951:Btk protein, mouse