Characterization of the common acute lymphoblastic leukaemia antigen (CD10) as an activation molecule on mature human B cells.

Distinct expression pattern of CD10 molecules during B cell activation was analysed using in vivo and in vitro systems. By two-colour flowcytometrical analysis, CD10 was found to be expressed at a specific stage of in vivo activating B cells. The expression of CD10 during B cell activation appeared to be unique from that of other activation-related B cell antigens including L29, MA6, OKT9 and OKT10. Although the expression of CD10 was associated with that of the activation-related B cell antigens, CD10+ B cells could be separated in the distinct fractions to those expressing other activation-related B cell antigens when fractionated by cell gravity. In particular, certain CD10+ B cells were detected positive for the resting B cell antigen, L30. In vitro studies revealed that CD10+ B cells arose from CD10- B cells at an early step of B cell activation, and disappeared lately when activated by Staphylococcus aureus Cowan I. Collectively, CD10 was an antigen transiently expressed at an early phase of B cell activation process. Expression of CD10 and other antigens on Burkitt's lymphomas (15 cases) was studied next. All cases were CD10+, and 87% (13 cases) were also L30+. In addition, six of CD10+ L30+ cases were L29+. This observation suggested that Burkitt's lymphomas were phenotypically similar to the B cells at an early phase of activation, those expressing CD10 and L30, simultaneously. The present study has dissected a precise expression pattern of CD10 on mature B cell activation in vitro and in vivo, and could be implicated for the histogenesis of one of the poorly characterized B cell lymphoma, namely Burkitt's lymphoma.