Functional activity of CD40 antibodies correlates to the position of binding relative to CD154

In this study we describe the characterization of a panel of 12 anti-mouse CD40 monoclonal antibodies (mAb). Characterization was performed in terms o f antibody-binding site relative to the CD154 ligand, and the relationship between position and functional outcome of binding. The antibodies divided into three groups. The first were strong inhibitors of CD154 binding, and i nduced strong proliferative and activation signals to B cells. Two antibodi es gave intermediary inhibition and comparable levels of activation. The re maining antibodies were found to bind outside the CD154 binding site and we re poor inducers of B-cell activation. Data presented show a strong correla tion between location of mAb binding and the resultant activation signal de livered. This correlation is shown to be independent of the isotype of the antibody involved and of its affinity. Implications of these findings are d iscussed.