II. The B5 Monoclonal Human Autoantibody Binds to Cell Surface TNFα on Human Lymphoid Cells and Cell Lines and Appears to Recognize a Novel Epitope

A human IgM monoclonal antibody (B5) recognizing human TNFα was established from peripheral blood lymphocytes by transformation with Epstein-Barr virus and subsequent cell fusion. The B5 monoclonal antibody (mAb) binds to cell surface TNFα (csTNFα) on human T cells, B cells, and monocytes. In addition, this autoantibody binds to csTNFα on a variety of lymphoid and monocyte lineage cell lines of human origin, as well as astrocytomas, a breast carcinoma, and a melanoma. Interestingly, the B5 mAb also binds to chimpanzee lymphocytes and to mouse T lymphoma cell line csTNFα. Many neutralizing mouse anti-TNFα mAbs do not exhibit comparable binding to csTNFα. This is consistent with the previous demonstration that B5 recognizes an epitope on TNFα distinct from those recognized by three neutralizing mouse anti-TNFα mAbs. B5 binding to csTNFα is specific since it can be inhibited by TNFα. No inhibition of B5 binding was seen by a neutralizing mouse anti-TNFα mAb. The B5 autoantibody appears to recognize the transmembrane form of TNFα and most likely also recognizes TNFα associated with its receptor. The unique specificity of this B5 autoantibody provides some additional insight into the complex physiology of cell surface-associated TNFα.