In vitro cytokine production and growth inhibition of lymphoblastoid cell lines by CD4+ T cells from Epstein-Barr virus (EBV) seropositive donors.

Abstract

In vitro stimulation of peripheral blood lymphocytes (PBL) from healthy Epstein-Barr Virus (EBV) seropositive individuals with autologous lymphoblastoid cell lines (LCL) gives rise to CD4+ and CD8+ T cells both of which are cytotoxic for autologous lymphoblastoid cells. Activated EBV-specific CD4+ T cells are cytotoxic towards autologous LCL but, paradoxically, CD4+ T cells have also been shown to enhance tumour formation in SCID/Hu mice. Here, we show that despite being cytotoxic, CD4+ T-cell lines from different donors show considerable variation in their ability to inhibit the long-term growth of autologous LCLs in vitro. Following re-stimulation in vitro with PMA and ionomycin, CD4+ T cells produced IFNgamma, TNFalpha, TNFbeta, IL-2, IL-4, IL-10 and IL-13. TNFalpha, TNFbeta and IL-10 production were also detected in LCL. IL-6 was only detected in trace amounts in either cell type. The ratio of IFNgamma to IL-4 production varied between the CD4+ T-cell lines, indicating differences in the Th1/Th2 balance of the response. When CD4+ T cells were re-stimulated using autologous LCL as antigen-presenting cells, they produced more IL-4 and less IFNgamma or IL-13 when compared with cells re-stimulated by phorbol myristate acetate (PMA) and ionomycin. Using two colour cytokine staining, we showed that many individual CD4+ T cells produced IFNgamma along with either IL-4 or IL-13. Purified CD4+ T cells completely inhibited the outgrowth of autologous LCL in five out of nine cases, and partially inhibited outgrowth in the remaining four. There was no correlation between the pattern of CD4+ T-cell cytokine production and the capacity to inhibit outgrowth of autologous LCL. The killing of LCLs was contact-dependant and not mediated by soluble factors. We conclude that the ability of CD4+ T cells to inhibit autologous LCL growth is not directly related to T-helper cell cytokine production, but may depend on cytoxicity through surface ligands such as CD95L (FasL) and TNFalpha-related apoptosis-inducing ligand (TRAIL).