IMMUNOBIOLOGY A novel human B cell subpopulation representing the initial germinal center population to express AID

We have identified a novel mature hu-man B-cell subpopulation in the human tonsil that has characteristics of both naive B cells and germinal center B cells including the expression of activa-tion-induced cytidine deaminase (AID), which is essential for the process of immunoglobulin somatic hypermuta-tion and class-switch recombination. These cells are clearly somatically hy-permutated, albeit modestly. Their phe-notype (IgDCD38CD23FSChiCD71) is unique and suggests they may be intermediate between both naive and germinal center cells. Morphologically they are also distinct from other B-cell subpopulations. The evidence presented suggests these cells may be the founder cells of the germinal center reaction (a pro-GC cell) and may be the normal counterpart of the mantle cell lym-phoma cell. (Blood. 2007;109:2545-2552) © 2007 by The American Society of Hematolog