CM1, a possible novel activation molecule on human lymphocytes

CMI (centrocyte/-blast marker 1) defined by a mAb developed against concana valin-A activated PBMC, is expressed specifically on some tonsillar germina l center (GC) B cells. In single flow cytometric analysis, the bone marrow did not express these molecules nor did the PBMC or the thymocytes. The per ipheral B lymphocytes showed more than 90% positive, while the peripheral T lymphocytes showed approximately 60% positive at 48 h after activation by PMA/ionomycin, respectively. A western blot analysis and an immunoprecipita tion for CM1 showed a band at 70 kDa. Cross-linking of CM1 with anti-CM1 mA b induced apoptosis of the GC B cells (CD38(+)IgD(-)). Immunohistochemical staining revealed that the CM1 molecule is distributed over the entire area except the proximal dark zone of the tonsillar germinal centers. These res ults suggest that the CM1 molecule might be involved in differentiation of the germinal center B cells as one of the novel centrocyte markers. (C) 200 0 Elsevier Science B.V. All rights reserved.