MOUSE CD38 IS DOWN-REGULATED ON GERMINAL CENTER B-CELLS AND MATURE PLASMA-CELLS

Germinal center formation is the result of antigenic stimulation of B cells in a T cell-rich area. B cells cycle through the germinal center s, and a small percentage survive to become plasma cells or memory B c ells. The transformation from a mature B cell into a germinal center B cell and finally into a terminally differentiated B cell is not well understood. Human CD38 is highly expressed on both germinal center B c ells and plasma cells, and is useful in delineating these B cell subse ts and in understanding the signaling events involved in the developme nt of these B cells. To determine whether CD38 expression on activated germinal center B cells and postgerminal center B cells influences ge rminal center differentiation, we studied the expression of CD38 in th e mouse. CD38 is expressed on follicular B cells in the Peyer's patche s but is down-regulated on germinal center B cells located within the Peyer's patches. CD38(dim/-)B220(+) germinal center B cells are also f ound in the spleens of immunized but not control mice, suggesting that Ag-stimulated germinal center formation is involved in the production of CD38(dim/-)B220(+) B cells. Furthermore, mature plasma cells isola ted from in vitro LPS cultures do not express CD38, but do contain hig h levels of cytoplasmic Ig. These results are in contrast to studies i n humans in which CD38 is not found on follicular B cells but is highl y expressed on germinal center B cells and plasma cells.