In vivo and in vitro stimulation of mouse spleen leukocytes by BL-20803, a low-molecular-weight interferon inducer.

BL-20803, a low-molecular-weight compound, although able to elicit circulating interferon in the mouse, failed to protect cultured cell lines in vitro from infection by interferon-sensitive viruses. Of the tissues analyzed for interferon content after oral administration of the drug to mice, spleen and lung contained the largest amounts of the virus inhibitor. Spleen cells from such dosed animals when isolated into in vitro cultures elaborated small amounts of interferon into the culture medium. The time sequence of acquisition by spleen cells of the ability to produce interferon closely correlated with the kinetics of development of the circulating interferon response in the intact mouse. When spleen cells were separated on the basis of adherence or nonadherence to a plastic surface, the bulk of the interferon activity was found to be associated with the adherent cells. Upon exposure to BL-20803 in cell culture, adherent cells and, to a lesser extent, nonadherent cells from untreated mice were stimulated to produce interferon-like activity. The biological behavior of BL-20803 is shown to have striking similarities with that of the structurally different low-molecular-weight inducer tilorone hydrochloride.