Human peripheral blood null lymphocytes stimulated by Staphylococcus aureus Cowan I produce atypical acid-labile interferon in vitro.

Peripheral blood mononuclear leucocytes (PBLs) stimulated in vitro by heat-killed formaldehyde-fixed Staphylococcus aureus Cowan I (SACoI) produced acid-labile alpha interferon (IFN-alpha) and, to various extents, also IFN-gamma. The IFN producers resided in nylon wool-nonadherent cells, and monocytes suppressed SACoI-induced IFN responses. Further separation of nonadherent PBLs in accordance with expression of surface antigenic markers was performed with a 'panning' technique. The SACoI induced production of IFN in cells that carried neither surface immunoglobulins nor OKT3-defined antigens. These cells were also characterized as OKM1- and OKT10-negative. In contrast, cells with natural killer (NK) activity against K562 erythroleukaemia cells were located in both OKM1- and OKT10-positive and -negative cells. At centrifugation on Percoll density gradients, cells with NK activity and IFN response against SACoI were recovered from light gradient fractions that contained mainly large granular lymphocytes (LGL). Furthermore, the IFN producers were enriched by removal of sheep erythrocyte-rosetting T cells from the Percoll fractions. These SACoI-induced IFN-producing PBLs are LGL but lack certain antigens that are frequently found on NK cells.