Induction of Gamma Interferon by Endotoxin in “Aged” Murine Splenocyte Cultures

Abstract

Escherichia coli lipopolysaccharide (LPS) is a lymphocyte mitogen and stimulator of the immune response. It is known to induce alpha/beta interferon (IFN) in murine splenocyte cultures when added at culture initiation. However, in the present study, “aged” populations of splenocytes were seen to produce gamma IFN when stimulated by LPS. Whole spleen cell cultures, which were allowed to incubate 24, 48, or 72 hours before the addition of 10 µg/m1 endotoxin, elaborated approximately 150 units of IFN per ml of culture fluid. All but about 20% of this antiviral activity was neutralized by monoclonal antibody to gamma IFN. Furthermore, the addition of 10 µg/ml polymyxin B to 48-hour cultures resulted in the abrogation of gamma IFN and alpha/beta IFN production, demonstrating that LPS is responsible for the induction of both types of IFNs. Aged adherent spleen cell cultures produced a mixture of IFNs, the majority of which was not neutralizable by anti-IFN-gamma, suggesting that macrophages produced predominantly alpha/beta IFN in response to LPS regardless of time in culture. In other experiments, whole spleen cell cultures were depleted of T cells by treatment with anti-Thy 1.2 plus complement and then stimulated with endotoxin. The addition of LPS to T-depleted populations at the start of incubation resulted in a predominantly alpha/beta response, as expected. However, the production of gamma IFN in response to LPS in aged spleen cell cultures was abrogated by T cell depletion.