Interferon-α-dependent and -independent participation of accessory cells in natural killer cell-mediated lysis of HSV-1-infected fibroblasts

Human natural killer (NK) cells require an HLA-DR⁺ accessory cell (AC) population to lyse herpes simplex virus-type 1 (HSV-1)-infected fibroblasts (HSV-Fs) but not K562 target cells. It has been postulated that ACs may function by producing interferon-α (IFN-α), which stimulates NK cells. Using a sequential enrichment protocol, ACs were found to coenrich with the interferon-producing cells (IPCs). Treatment of the ACs with a protein synthesis inhibitor, emetine, inhibited both their IFN production and AC function, results that support a central role for IFN in AC activity. In contrast, when the arginine analogue canavanine was added to NK assays, no IFN-α was produced and NK(HSV-Fs) activity was only partially inhibited. Consistent with IFN-independent AC function, treatment with either polyclonal sheep or bovine anti-IFN-α neutralized all the IFN-α produced during the NK assays but caused either no or partial reduction of NK(HSV-Fs) activity, respectively. However, when limiting numbers of ACs were used, the bovine antiserum neutralized both IFN-α and NK(HSV-Fs) activity. We further found that HLA-DR⁺ cells are required for cell clustering, suggesting a role for cell contact. Finally, fixation of activated ACs prevented the accessory function. Together, these results demonstrate that ACs can provide help to NK cells in both IFN-α-dependent and -independent manners.