Generation of lipopolysaccharide-induced interferon in spleen cell cultures. I. Genetic analysis and cellular requirements

Interleukin-18 Regulation of Interferon γ Production and Cell Proliferation as Shown in Interleukin-1β–Converting Enzyme (Caspase-1)-Deficient Mice

Interleukin-18 (IL-18) is a costimulatory factor for interferonγ (IFNγ) production. Processing of pro–IL-18 by IL-1β–converting enzyme (ICE) leads to the release of bioactive IL-18. Compared with wild-type (WT) mice, splenocytes from ICE-deficient mice produced low IFNγ after lipopolysaccharide (LPS) or zymosan (50% and 80% reduction). In contrast, IFNγ production was unimpaired in ICE-deficient mice using Concanavalin A (Con A). Comparable results were obtained when endogenous IL-18 was blocked with a neutralizing antibody. LPS-induced IFNγ was also reduced by an ICE inhibitor. Exogenous IL-18 augmented zymosan-induced IFNγ production in WT mice. In ICE-deficient cells, IFNγ production was only partially restored by IL-18. The reduced levels of IFNγ in ICE-deficient mice were not due to a lack of IL-12, because zymosan induced IL-12 equally in WT and in ICE-deficient mice. IFNγ is an important regulator of cell proliferation. In accordance, splenocytes from ICE-deficient mice proliferated more when stimulated with LPS, but not with Con A. Furthermore, in ovalbumin-sensitized ICE-deficient mice, proliferation of lymph node cells in response to the specific antigen was not altered. Exogenous IFNγ inhibited, whereas blockade of endogenous IFNγ or IL-18 increased, LPS induced splenocyte proliferation both in WT and in ICE-deficient mice. Our results show that IL-18 is an IL-12–independent regulator of IFNγ production and of cell proliferation induced by microbial stimuli. However, ICE-dependent processing of IL-18 is not needed for response to mitogens or antigens.

Interleukin-18 Regulation of Interferon γ Production and Cell Proliferation as Shown in Interleukin-1β–Converting Enzyme (Caspase-1)-Deficient Mice

Interleukin-18 (IL-18) is a costimulatory factor for interferonγ (IFNγ) production. Processing of pro–IL-18 by IL-1β–converting enzyme (ICE) leads to the release of bioactive IL-18. Compared with wild-type (WT) mice, splenocytes from ICE-deficient mice produced low IFNγ after lipopolysaccharide (LPS) or zymosan (50% and 80% reduction). In contrast, IFNγ production was unimpaired in ICE-deficient mice using Concanavalin A (Con A). Comparable results were obtained when endogenous IL-18 was blocked with a neutralizing antibody. LPS-induced IFNγ was also reduced by an ICE inhibitor. Exogenous IL-18 augmented zymosan-induced IFNγ production in WT mice. In ICE-deficient cells, IFNγ production was only partially restored by IL-18. The reduced levels of IFNγ in ICE-deficient mice were not due to a lack of IL-12, because zymosan induced IL-12 equally in WT and in ICE-deficient mice. IFNγ is an important regulator of cell proliferation. In accordance, splenocytes from ICE-deficient mice proliferated more when stimulated with LPS, but not with Con A. Furthermore, in ovalbumin-sensitized ICE-deficient mice, proliferation of lymph node cells in response to the specific antigen was not altered. Exogenous IFNγ inhibited, whereas blockade of endogenous IFNγ or IL-18 increased, LPS induced splenocyte proliferation both in WT and in ICE-deficient mice. Our results show that IL-18 is an IL-12–independent regulator of IFNγ production and of cell proliferation induced by microbial stimuli. However, ICE-dependent processing of IL-18 is not needed for response to mitogens or antigens.

Interferon gamma (IFN-gamma) production by gut-associated lymphoid tissue and spleen following oral Salmonella typhimurium challenge

Although IFN-gamma has been shown to play an important role in protection against a systemic S. typhimurium challenge, the in vivo and in vitro production of this cytokine following S. typhimurium infection of the gastrointestinal tract has not been investigated. In this study, IFN-gamma production by gut-associated lymphoid tissue and spleen was investigated in mice following oral challenge with S. typhimurium. Cells obtained from the Peyer's patches (PP), mesenteric lymph nodes (MLN) and spleen (Sp) of mice orally challenged with S. typhimurium were assessed for levels of IFN-gamma mRNA after varying times following in vivo infection. RNA obtained from the above tissues was subjected to reverse transcription followed by PCR amplification using primers specific for murine IFN-gamma. Elevated levels of IFN-gamma mRNA were first detected in the PP at 6 h post-challenge. Elevated levels of IFN-gamma mRNA were then detected in the MLN at 24 h and in the spleen at 4 days post-challenge. These in vivo results were in agreement with the ability of these lymphoid tissues to produce IFN-gamma upon in vitro stimulation with killed S. typhimurium. Neutralization of endogenously produced IFN-gamma by administration of mAb to IFN-gamma completely abrogated resistance to an oral challenge of S. typhimurium. A significant difference in the percent mortality was observed between the antibody-treated and control groups. Evaluation of bacterial spread in the antibody treated group versus the control group at 4 days following oral challenge revealed higher numbers of bacteria in the spleen and liver of antibody treated mice. These results clearly show that IFN-gamma is rapidly produced by gut-associated lymphoid tissue and spleen following oral S. typhimurium infection, and that endogenous production of IFN-gamma is essential in host resistance to S. typhimurium.

Local interferon induction by bacterial lipopolysaccharide in mice after pretreatment with Corynebacterium parvum

C57BL/6 mice were injected intraperitoneally (i.p.) with Corynebacterium parvum and subsequently, after an interval of 7-10 days, i.p. with lipopolysaccharide (LPS). The peritoneal wash-fluid was recovered at various times after injection of LPS. Marked interferon (IFN) titers were observed between 2 and 10 h after injection of LPS, whereas no IFN was detected in mice injected with either C. parvum or LPS alone. Very low doses of LPS (0.1 microgram/mouse) were sufficient to cause IFN production in the double-stimulation protocol. The IFN produced was neutralized by an antibody against IFN-alpha/beta. In additional experiments, mice were treated by C. parvum alone; the peritoneal exudate cells (PEC) were recovered and stimulated in vitro by LPS. Again substantial titers of IFN were induced by small concentrations of LPS, whereas untreated PEC did not produce IFN. The cell producing IFN in these cultures was not a T lymphocyte, as experiments with a monoclonal anti-thy 1.2 antibody showed.

Role of interferon in the resistance of C3H/HeJ mice to infection with herpes simplex virus

C3H/HeJ mice known to be defective in their responses to bacterial lipopolysaccharides, are more resistant to infection with herpes simplex virus (HSV) than the closely related strain C3HeB/FeJ. The increased resistance is reflected in higher early local interferon titers after HSV infection. However, NK cell activation by HSV is not correlated with resistance, since the NK cell response of C3H/HeJ mice was significantly lower than that of the control strain.