I. A Novel Monoclonal Human IgM Autoantibody which Binds Recombinant Human and Mouse Tumor Necrosis Factor-α

Several monoclonal human IgM antibodies to recombinant human tumor necrosis factor-α (rhTNFα) have been generated and partially characterized. The F78-1A10-B5 monoclonal antibody (mAb) (B5) binds to rhTNFα with a titer comparable to three high-affinity neutralizing mouse mAbs, when tested by ELISA. However, the B5 mAb binds relatively weakly to soluble rhTNFα. It appears to bind to epitopes on rhTNFα distinct from those bound by the mouse mAbs for three reasons. First, preincubation of plate-bound rhTNFα with mouse mAbs does not decrease or compete subsequent B5 mAb binding. Second, rhTNFα complexed to the mouse mAbs can still be bound by B5 mAb. Third, the mouse mAbs neutralize TNFα cytotoxicity whereas the B5 mAb does not. Binding analyses indicate that this human IgM autoantibody binds to both human and mouse recombinant TNFα but not to other antigens commonly recognized by polyreactive natural IgM autoantibodies. The high level of amino acid identity between the human and mouse TNFα molecules suggest that the B5 mAb is monospecific for a given epitope shared by these two forms or TNFα. This spectrum of characteristics makes B5 a novel mAb.