title: The cellular context of AID expressing cells in fish lymphoid tissues.
abstract: It has long been held that the cold-blooded vertebrates lack mammalian-like germinal centers, though they do have affinity maturation and the immunoglobulin mutator activation-induced cytidine deaminase or AID. Using AID as a marker of sites of somatic hypermutation, we have identified discrete cell clusters of up to several thousand cells, in the spleen and kidney of channel catfish (Ictalurus punctatus), which may be primordial germinal centers. In situ hybridization revealed that AID expressing cells are interspersed or surrounded by a population of pigmented CSF1-R expressing cells called melano-macrophages. Significantly, melano-macrophages or associated reticular cells have been previously noted for their ability to retain soluble antigen on or near their surface for several weeks following vaccination. Laser capture microdissection and RT-PCR were used to establish that these cell clusters also contained cells expressing Ig heavy chain transcripts as well as transcripts of TcRbeta and the putative CD4 homologue of fish. These observations, coupled with past work showing that mutations develop in B-cell lineages in fishes, allow us to develop a model for how affinity maturation may have evolved in early gnathostome vertebrates.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, T6G-2E5 Canada.
authors.forename: Holly L
authors.initials: HL
authors.lastname: Saunders
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Oko
authors.forename: Amanda N
authors.initials: AN
authors.lastname: Scott
authors.forename: Chia Wei
authors.initials: CW
authors.lastname: Fan
authors.forename: Brad G
authors.initials: BG
authors.lastname: Magor
mesh_terms: D000818:Animals; D000915:Antibody Affinity; D015415:Biomarkers / Q000378:metabolism*; D015704:CD4 Antigens / Q000276:immunology; D002460:Cell Line; D003564:Cytidine Deaminase / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D029941:Fish Proteins; D019674:Genes, T-Cell Receptor beta / Q000276:immunology; D007059:Ictaluridae; D056724:Immunity, Humoral; D007136:Immunoglobulins; D017403:In Situ Hybridization; D007668:Kidney / Q000276:immunology / Q000378:metabolism*; D008221:Lymphoid Tissue / Q000276:immunology / Q000378:metabolism*; D008543:Melanins / Q000378:metabolism; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D027041:Somatic Hypermutation, Immunoglobulin; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D015415:Biomarkers; D015704:CD4 Antigens; D029941:Fish Proteins; D007136:Immunoglobulins; D008543:Melanins; D016186:Receptor, Macrophage Colony-Stimulating Factor; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase