A new multivalent B cell activation model-anti-IgD bound to FcγRI: Properties and comparison with CD40L-mediated activation

CHO cells permanently transfected with mouse FcγR1 a chain were prepared and used as a model to polyclonally activate murine B cells. The transfected CHO cells were treated with mitomycin C and placed into culture with varying quantities of anti-IgD. Using this model, murine splenic a cells (from BALB/c or C57BI/6) were activated by mouse IgG2a-anti-IgD (10.4.22 or AF3.33) in a manner that is analogous to the activation of a cells seen with highly polyvalent anti-IgD (Hδ^a/1) prepared by chemical cross-linking to dextran. Efficient B cell activation was seen with nanogram quantities of anti-IgD. In the presence of IL-4 and IL-5, IgG1 production levels were equivalent to or better than seen when stimulation was with Hδ^a/1-dextran; however, IgE induction was not seen in either situation. The Ig production capacity was compared to that seen when a cells were activated with CD40L, using either CD40L-transfected CHO or a soluble CD40L construct. In the presence of IL-4 and IL-5, once a critical threshold of B cells was present, IgE and to a lesser extent IgG1 production was inversely proportional to a cell number when CD40L was the activating agent. In contrast, with FcγRI-antiIgD, IgM and IgG1 production was directly proportional to a cell number, while IgE production was never seen. Finally, when a cells were co-activated with immobilized anti-IgD and CD40L simultaneously, the IgE production from B cells induced by CD40L was strongly inhibited, while IgG1 and IgM production were not affected. Since a cell co-activation via slg and CD40L would be a common scenario in secondary follicles, this inhibition of IgE production may be one of the reasons why serum IgE levels are much below IgG in normal immune situations.