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Updated: Aug 8, 2026
Generation of Human CD40-activated B cells
Published on: October 17, 2009
Stimulation of B lymphocytes via CD72 (human Lyb-2)
Insights
A CD72 antibody selectively activates human B lymphocytes, enhancing responses to certain stimuli like IgM. This antibody also increases MHC class II DQ antigen expression and promotes cell cycle entry in resting B cells.
Area of Science:
- Immunology
- Cell Biology
Background:
- CD72 is a human B lymphocyte surface molecule homologous to murine Lyb-2.
- B cell activation involves complex signaling pathways influenced by various surface molecules and cytokines.
Purpose of the Study:
- To investigate the functional role of CD72 in human B lymphocyte activation.
- To characterize the signaling pathways modulated by a CD72 monoclonal antibody.
Main Methods:
- Utilized tonsillar B lymphocytes from human donors.
- Employed [3H]dThd incorporation assays to measure B cell proliferation.
- Analyzed surface antigen expression (MHC class II DQ, IgM, CD23) via flow cytometry.
- Performed co-stimulation assays with various B cell activators (IL-4, anti-CD40, phorbol ester, ionophore).
Main Results:
- CD72 antibody weakly stimulated resting B cells, with modest enhancement by IL-4 or anti-CD40.
- CD72 signaling synergistically enhanced responses to immobilized anti-IgM but not soluble anti-IgM.
- CD72 antibody increased MHC class II DQ expression and induced G0 to G1 cell cycle transition, mimicking IL-4 effects.
- CD72 antibody did not up-regulate surface IgM or CD23 expression.
- Rapidly cycling B cells were unresponsive to CD72 signaling.
Conclusions:
- CD72 antibody activates specific B cell pathways, distinct from IL-4.
- CD72 plays a role in modulating B cell responses, particularly in conjunction with BCR signaling and MHC class II expression.
- CD72 signaling influences resting B cell activation and differentiation stages.
Abstract:
A monoclonal antibody to CD72, the 45-kDa human homolog of murine Lyb-2, was found to augment selective activation pathways in tonsillar B lymphocytes. By itself, CD72 antibody provided a weak direct stimulus to resting B cells as assessed by [3H]dThd incorporation; this was modestly enhanced on the addition of interleukin 4 (IL4) or following ligation of surface CD40. CD72-delivered signals were more evident in co-stimulation assays with phorbol ester and with a synergistic combination of IL4 and CD40 antibody, but not with calcium ionophore or a CD23 antibody; rapidly cycling B cells were refractory to signaling via CD72 whether or not other co-stimuli were present. A unique feature of the CD72-delivered signal was its ability to enhance synergistically stimulations triggered with immobilized antibody to IgM, while failing to augment responses initiated by soluble anti-mu. On direct culture of resting B lymphocytes with CD72 antibody, an approximately twofold increase in the expression of major histocompatibility complex class II DQ antigen was observed, an augmentation similar to that achieved with IL 4; CD72 antibody also mimicked IL 4 in its ability to drive G0 cells into the early G1 phase of cell cycle. In contrast to IL 4-promoted stimulation, CD72 antibody failed to up-regulate the surface expression of either IgM or the CD23 antigen. CD72 expression itself was found to be weak on resting B lymphocytes and was modestly enhanced following culture with IL 4. The findings are discussed with reference to observations made on the triggering of murine B lymphocytes through Lyb-2 and within the context of previously defined human B cell activation pathways.
