Binding of the Epstein-Barr virus major envelope glycoprotein gp350 results in the upregulation of the TNF-alpha gene expression in monocytic cells via NF-kappaB involving PKC, PI3-K and tyrosine kinases.

Epstein-Barr virus (EBV) is a human herpesvirus that interacts with various immunocompetent cells that carry the EBV receptor (CD21/CR2). EBV binds to CR2 through its major envelope glycoprotein 350 (gp350). Previously we had demonstrated that EBV and other human herpesviruses are capable of modulating cytokine synthesis through the deregulated expression of cytokine genes interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interleukin-2 (IL-2). Here we show that, in contrast to infectious EBV, purified recombinant gp350 upregulates TNF-alpha gene expression in human monocyte/macrophages (M/M) as well as in a monocytoid cell line, U937. Our results also demonstrate that this increased expression is due to both enhanced transcription and stability of TNF-alpha mRNA in gp350-treated cells. The specificity of this effect is evidenced by the fact that pre-incubation of cells with anti-CR2 monoclonal antibody OKB7, which blocks binding of gp350 to CR2, inhibits the above mentioned effects of gp350. Furthermore, we demonstrate that activation of TNF-alpha by gp350 is mediated by NF-kappaB through signal transduction pathways involving PKC, PI3-K and tyrosine kinases. To our knowledge this is the first report describing the modulation of TNF-alpha gene expression by the EBV-gp350 molecule following its interaction with the viral receptor CR2 on cells of the monocytic lineage.