EBV infects human B lymphocytes and induces them to proliferate, to produce Ig, and to give rise to immortal cell lines. Although the mechanisms of B cell activation by EBV are largely unknown, the continuous proliferation of EBV-immortalized B cells is dependent, at least in part, upon autocrine growth factors produced by the same EBV-infected B cells. In the present studies we have examined the influence of monocytes on B cell activation by EBV and found that unlike peripheral blood T cells and B cells, monocytes enhance by as much as 30- to 50-fold virus-induced B cell proliferation and Ig production. Upon activation with LPS, monocytes secrete a growth factor activity that promotes both proliferation and Ig secretion in EBV-infected B cells and thus reproduces the effects of monocytes in these cultures. Unlike a number of other factors, rIFN-beta 2/B cell stimulatory factor 2 (BSF-2)/IL-6 stimulates the growth of human B cells activated by EBV in a manner similar to that induced by activated monocyte supernatants. In addition, an antiserum to IFN-beta that recognizes both IFN-beta 1 and IFN-beta 2 completely neutralizes the B cell growth factor activity of activated monocyte supernatants. These findings demonstrate that IFN-beta 2/BSF-2/IL-6 is a growth factor for human B cells activated by EBV and suggest that this molecule is responsible for B cell growth stimulation induced by activated monocyte supernatants. We have examined the possibility that IFN-beta 2/BSF-2/IL-6 might also be responsible for B cell growth stimulation by supernatants of EBV-immortalized B cells and thus may function as an autocrine growth factor. However, IFN-beta 2/BSF-2/IL-6 is not detectable in supernatants of EBV-immortalized B cells by immunoprecipitation. Also, an antiserum to IFN-beta that neutralizes IFN-beta 2/BSF-2/IL-6 fails to neutralize autocrine growth factor activity. This suggests that autocrine growth factors produced by EBV-immortalized B cells are distinct from IFN-beta 2/BSF-2/IL-6. Thus, the continuous proliferation of EBV-immortalized B cells is enhanced by either autocrine or paracrine growth factors. One of the mediators with paracrine growth factor activity is IFN-beta 2/BSF-2/IL-6.

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