Phenotypic and molecular characterization of human peripheral blood B-cellsubsets with special reference to N-region addition and J kappa-usage in Vkappa J kappa-joints and kappa/lambda-ratios in naive versus memory B-cellsubsets to identify traces of receptor editing processes

We identified a population of IgM(+)IgD(+) B-cells in the peripheral blood (PB) of humans that express somatically mutated V-region genes like classic al class switched or IgM-only memory B-cells and comprise around 15% of PB B-cells in adults. Mutated IgM(+)IgD(+) cells differ from unmutated naive I gM(+)IgD(+) cells in that they express the CD27 cell surface antigen. In ad dition, a very small subset of IgD-only B-cells was identified in the PB th at carried rearranged VH-genes with an extremely high load of somatic mutat ions (up to 60 mutations per gene). A common characteristic of the four som atically mutated subsets, which altogether comprise 40% of PB B-lymphocytes in adults, is the surface expression of CD27. This antigen may thus repres ent a general marker for memory B-cells in the human. Somatically mutated a nd unmutated PB B-cell subsets were analyzed for N-region addition and J ka ppa-usage in V-joints, and in addition for the respective dh-ratios: N-nucl eotides could be identified in a large fraction of V kappa-regions of all B -cell subsets, indicating that N-region insertion already occurs in the pre -germinal center (GC) phase of B-cell development. Both the J kappa-usage i n expressed V kappa J kappa-joints and the kappa/lambda-ratio from somatica lly mutated B-cells do not differ substantially from those of the unmutated cells, so that in terms of these parameters, a contribution of secondary V kappa J kappa-rearrangements in shaping the memory B-cell repertoire is no t detectable.