Interferons and the Colony‐Stimulating Factors IL‐3 and GM‐CSF Enhance the IFN‐α Response in Human Blood Leucocytes Induced by Herpes Simplex Virus

Human peripheral blood mononuclear cells (PBMC) were stimulated to produce interferon-alpha (IFN-alpha) by glutaraldehyde-fixed Herpes simplex virus type 1 (HSV)-infected WISH amnion cells in vitro. Different cytokines were included during the stimulation and tested for their ability to enhance the IFN-alpha response which occurs in the natural IFN-alpha producing (NIP) leucocytes. The total production of IFN-alpha and the numbers of IFN-alpha producing cells (IPCs) were increased by interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF). Their most marked effect was to reduce the time required for induction of the IPC by the HSV-infected cells, thereby causing both an earlier peak of IPC numbers and secretion of IFN-alpha. Addition of IFN-alpha 2b did not alter the kinetics of the IFN-alpha response in the same way as the two CSFs, but instead generally increased the IPC numbers and the production of IFN-alpha. The IL-3 and GM-CSF, especially in combination with IFN-alpha, had the most pronounced enhancing effects on IPC numbers when PBMC were induced at low cell concentrations. The cytokines IL-1, IL-2, IL-4, IL-6 or tumour necrosis factor-alpha (TNF-alpha) had no detectable effects on the IFN-alpha response. The results suggest that cytokines such as the CSFs and IFNs may be involved in the regulation of NIP cell functions.