Klein U, Rajewsky K, Küppers R
Institute for Genetics, University of Cologne, 50931 Cologne, Germany.
J Exp Med. 1998 Nov 2;188(9):1679-89. doi: 10.1084/jem.188.9.1679.
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 approximately 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 approximately 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 Vkappa genes. This might be due to an intrinsically lower mutation rate in kappa light chain genes compared with heavy chain genes and/or result from kappa 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.
免疫球蛋白（Ig）M+IgD+B细胞通常被认为代表未接触过抗原的幼稚B细胞，其表达的可变（V）区基因无体细胞突变。我们在此报告，与CD27阴性的IgM+IgD+B细胞相反，表达CD27细胞表面抗原的人IgM+IgD+外周血（PB）B细胞携带突变的V基因。IgM+IgD+CD27（+）B细胞在细胞表型方面类似于类别转换的仅IgM记忆细胞，在健康成年人中约占PB B淋巴细胞的15%。此外，还检测到极少量（<PB B细胞的1%）高度突变的仅IgD B细胞，它们可能代表仅IgD扁桃体生发中心和浆细胞的PB对应物。总体而言，成年人PB中的B细胞池约由40%的突变记忆B细胞和60%未突变的幼稚IgD+CD27（-）B细胞（包括CD5（+）B细胞）组成。在体细胞突变的B细胞中，VH区基因的体细胞突变负荷比重排的Vκ基因高两到三倍。这可能是由于κ轻链基因与重链基因相比固有突变率较低和/或由于GC B细胞中κ轻链基因重排所致。体细胞突变的B细胞亚群的一个共同特征是CD27细胞表面抗原的表达，因此它可能代表人类记忆B细胞的一个通用标志物。
