IDENTIFICATION OF A NOVEL SUBPOPULATION OF GERMINAL CENTER B-CELLS CHARACTERIZED BY EXPRESSION OF IGD AND CD70

CD27, which belongs to the tumor necrosis factor receptor family, is e xpressed on germinal center (GC) but not on naive B cells, suggesting an important function of this molecule in the regulation of the GC rea ction. We described here the expression of CD70, which is the ligand f or CD27. We observed that in most tonsils, CD70 is only expressed on p art of the IgD(-). CD38(-) B cell population, which have been describe d as memory B cells. However, in 10% of the tonsils tested, CD70(+)IgD (+) GC were found. The CD70(+) GC B cells were small cells that also e xpressed CD44 and CD39, but were CD10(-) and CD38(-), suggesting that they represent very recent immigrants that are in the process of formi ng a GC. The concordant expression of CD27 and its ligand CD70 on this primordial subset of GC B cells suggests an important role for CD27/C D70 interaction at this stage of GC formation.