Decreased frequency of functional natural interferon-producing cells in peripheral blood of patients with the acquired immune deficiency syndrome

Deficient in vitro production of interferon-α (IFN-α) in response to herpes simplex virus (HSV) occurs in patients infected with the human immunodeficiency virus (HIV), with the most deficient responses associated with opportunistic infections (OI). The peripheral blood mononuclear cells (PBMC) which produce IFN-α in response to HSV are light density, HLA-DR⁺ cells lacking any unique surface markers and have been termed “natural interferon-producing cells” (NIPC). In this study, IFN-α responses were measured and the ELISpot assay was utilized to determine the frequency of NIPC in response to HSV. As expected, HIV-infected patients had depressed IFN-α production. In the ELISpot assay, healthy controls had a mean frequency of 1:703 NIPC among PBMC; each NIPC made approximately 2 international units (IU) of IFN-α. HIV-infected patients on average had fourfold less NIPC than controls and produced 1 IU IFN-α/NIPC; the plaque size for patient samples was often smaller than that for controls. NIPC frequency and IFN-α production were lowest in patients with a history of OI. In conclusion, deficient IFN-α production by AIDS patients results from reductions in both the frequency and the activity of NIPC, probably reflecting a gradual turning off of IFN-α production.