Human monoclonal antibodies produced by Epstein-Barr virus transformed cell lines bind protein A

Epstein-Barr virus (EBV) is a polyclonal T-independent activator of viral receptor positive human B lymphocytes. Lymphocytes infected in vitro with the virus are transformed into immortalized cell lines [Nilsson, K. and Klein, G. (1982) Adv. Cancer Res. 37, 319]. In this way human cell lines that secrete specific IgM, IgG and IgA monoclonal antibodies are established. Protein A is also a polyclonal T-independent B cell activator [Langone, J. J. (1982) Adv. Immunol. 32, 157], the targets of which are surface immunoglobulin and C3d receptor positive cells, as are the targets of EBV. We found that almost all (16 out of 17) of the specific monoclonal antibodies (IgM, IgG and IgA) produced in vitro by EBV cell lines bind protein A. Unlike these in vitro produced antibodies, a substantial fraction of the immunoglobulins in human serum does not bind protein A. Thus, those plasma cells which in vivo secrete protein A nonbinding immunoglobulins originate from precursors of B cell that were EBV noninfective. Alternatively, during in vivo B differentiation some immunoglobulins undergo a change from protein A binding to protein A nonbinding molecules.