Ligation of CD80 provides stimulatory signals in normal and clonal B cells distinct from CD40

The proliferative capacity of B-CLL cells in vitro is impaired in experimental systems which otherwise provide sufficient stimulation of normal B cells, including the CD40 pathway. We observed that this defect can be overcome by coculturing B-CLL cells in direct contact with activated T helper cells. We reasoned that additional antigen-independent signals besides the CD40 pathway might contribute to T cell-mediated stimulation. To investigate the role of ligation of T cell-associated molecules in normal and clonal B cells we used Cdw32 transfected murine L cells to present several antibodies to B cells in combination with IL-2. The most striking effects were observed upon stimulation with CD80 antibodies. Induction of cytokine secretion, such as IL-6, IL-8 and TNF-α, was seen in the majority of samples from B-CLL patients and normal controls. IL-6, in particular, was more effectively induced by CD80 mAB + IL-2, as compared to CD40 mAB + IL-2. In addition, a proliferative response was obtained by CDSOmAB + IL-2 in CLL patients, which was equivalent or higher to stimulation by CD40. In normal peripheral blood B cells, proliferation was observed using CDSOmAB, as well, although at a lower level. Secretion of IgM was stimulated by CD80 and further enhanced by the combination with CD40, whereas IgG and IgA production was not affected. We conclude that ligation of CD80 induces significant biological responses in normal and clonal B cells, suggesting an alternative pathway of antigen-independent stimulation by accessory T cells.