title: A new memory CD27-IgG+ B cell population in peripheral blood expressing VH genes with low frequency of somatic mutation.
abstract: In humans, up to 40% of peripheral B cells express CD27 and have hypermutated variable regions in their Ig genes. The CD27+ B cells are considered to be derived from germinal center following specific antigenic stimulation. Actually, somatic hypermutation in Ig genes and CD27 expression are hallmarks of memory B cells. However, the blood IgM+ IgD+ CD27+ B cells were recently associated to splenic marginal zone B cells and proposed to be a subset distinct from germinal center-derived memory B cells showing premutated Igs. The results presented herein further weaken this bona fide association because B cells expressing surface IgG, but not CD27, were found in human blood. Representing 1-4% of all peripheral B cells and approximately 25% of the IgG+ blood B cells, this population expressed mutated IgG genes showing antigenic selection characteristics but with lower mutation frequencies than that of CD27+ IgG+ B cells. However, their morphology and phenotype were similar to that of CD27+ IgG+ cells. Interestingly, the proportion of IgG2 over IgG3 transcripts was opposite in CD27- IgG+ and CD27+ IgG+ cells, suggesting distinct functions or origins. Overall, these findings extend the memory B cell reservoir beyond the CD27+ compartment and could provide further insights into B cell disorders of unknown etiology.
authors.affiliation: Héma-Québec, Recherche et Développement, Sainte-Foy, Quebec, Canada.
authors.forename: Jessie F
authors.initials: JF
authors.lastname: Fecteau
authors.forename: Geneviève
authors.initials: G
authors.lastname: Côté
authors.forename: Sonia
authors.initials: S
authors.lastname: Néron
mesh_terms: D018941:Antigens, CD19 / Q000097:blood; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D002478:Cells, Cultured; D005787:Gene Frequency / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000096:biosynthesis* / Q000097:blood / Q000235:genetics; D007143:Immunoglobulin Heavy Chains / Q000096:biosynthesis / Q000097:blood / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000096:biosynthesis / Q000097:blood / Q000235:genetics*; D007156:Immunologic Memory / Q000235:genetics*; D027041:Somatic Hypermutation, Immunoglobulin; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7 / Q000096:biosynthesis / Q000097:blood*
chemical_list: D018941:Antigens, CD19; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7