Human Immunoglobulin (Ig)M+IgD+ Peripheral Blood B Cells Expressing the CD27 Cell Surface Antigen Carry Somatically Mutated Variable Region Genes: CD27 …

U Klein, K Rajewsky, R Küppers - The Journal of experimental medicine, 1998 - rupress.org
U Klein, K Rajewsky, R Küppers
The Journal of experimental medicine, 1998rupress.org
Immunoglobulin (Ig) M+ IgD+ B cells are generally assumed to represent antigen-
inexperienced, naive B cells expressing variable (V) region genes without somatic
mutations. We report here that human IgM+ IgD+ peripheral blood (PB) B cells expressing
the CD27 cell surface antigen carry mutated V genes, in contrast to CD27-negative IgM+
IgD+ B cells. IgM+ IgD+ CD27+ B cells resemble class-switched and IgM-only memory cells
in terms of cell phenotype, and comprise∼ 15% of PB B lymphocytes in healthy adults …
Immunoglobulin (Ig)M+IgD+ B cells are generally assumed to represent antigen-inexperienced, naive B cells expressing variable (V) region genes without somatic mutations. We report here that human IgM+IgD+ peripheral blood (PB) B cells expressing the CD27 cell surface antigen carry mutated V genes, in contrast to CD27-negative IgM+IgD+ B cells. IgM+IgD+CD27+ B cells resemble class-switched and IgM-only memory cells in terms of cell phenotype, and comprise ∼15% of PB B lymphocytes in healthy adults. Moreover, a very small population (<1% of PB B cells) of highly mutated IgD-only B cells was detected, which likely represent the PB counterpart of IgD-only tonsillar germinal center and plasma cells. Overall, the B cell pool in the PB of adults consists of ∼40% mutated memory B cells and 60% unmutated, naive IgD+CD27 B cells (including CD5+ B cells). In the somatically mutated B cells, VH region genes carry a two- to threefold higher load of somatic mutation than rearranged Vκ genes. This might be due to an intrinsically lower mutation rate in κ light chain genes compared with heavy chain genes and/or result from κ light chain gene rearrangements in GC B cells. A common feature of the somatically mutated B cell subsets is the expression of the CD27 cell surface antigen which therefore may represent a general marker for memory B cells in humans.
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