Methods for preventing or treating an antibody-mediated diease in a patient are presented, the methods comprising administration of a monoclonal antibody capable of binding to a human CD40 antigen located on the surface of a human B cell, wherein the binding of the antibody to the CD40 antigen prevents the growth or differentiation of the B cell. Monoclonal antibodies useful in these methods, and epitopes immunoreactive with such monoclonal antibodies are also presented.