Formation of tubuloreticular inclusions in mitogen-stimulated human lymphocyte cultures by endogenous or exogenous alpha-interferon.

Tubuloreticular inclusions (TRI) were induced in normal blood lymphocytes after incubation with Staphylococcus aureus Cowan 1 (STA), but they were not induced by pokeweed mitogen (PWM), as we reported previously. TRI were also induced in Raji cells when grown in the medium of STA culture. Alpha-interferon (alpha IFN) was detected only in the medium of STA culture and not in PWM culture. The cells of PWM cultures formed TRI when exposed to various concentrations of human leukocyte alpha IFN. The incidences of TRI-positive cells in the presence of 50-500 IU/ml of alpha IFN were 3-5% on day 2 and increased to 10% on day 7. On days 5-7 of the PWM cultures, plasmacytoid cells containing TRI were seen not infrequently. In the presence of a high concentration of alpha IFN (10,000 IU/ml), which was sufficient to inhibit cell growth and differentiation, the growth of the TRI region was not altered and the incidence of TRI-positive cells was 9% on day 2 and increased to 15% on day 7. Our observations suggest that the TRI formation in STA culture is attributable to the alpha IFN produced endogenously by STA-stimulated cells and that some relationship might exist between the incidences of TRI-positive cells in these mitogen-stimulated cultures and the biologic functions of IFN.