Endogenous IFN-gamma Production Research Articles

Interferon-gamma and resistance to bacterial infections.

Since its initial description as an antiviral, it has become clear that Interferon-gamma (IFN-gamma) has potent immunoregulatory and cell growth regulatory activities. As a result of these additional activities, it is now apparent that IFN-gamma plays a major role in regulation of bacterial infections. IFN-gamma can be both induced by bacteria and bacterial products; endogenous IFN-gamma production has been shown to play a protective role in the natural host response to several bacterial infections; and administration of exogenous IFN-gamma is effective in the prevention and treatment of bacterial infections in numerous animal model systems. Although it is now clear that IFN-gamma plays a role in regulation of bacterial infections, the mechanisms of its anti-bacterial effects in vivo remain to be established due to the pleiotropic nature of IFN-gamma activity.

Endogenous tumor necrosis factor, interleukin-6, and gamma interferon levels during Listeria monocytogenes infection in mice

Mice were infected intravenously with a sublethal dose of Listeria monocytogenes cells and then levels of tumor necrosis factor (TNF), interleukin-6 (IL-6), and gamma interferon (IFN-gamma) in the bloodstreams, spleens, and livers were monitored. The maximum level of TNF was detected at 72 h in the spleens and livers, but TNF was never detected in the bloodstreams. IL-6 appeared in the bloodstreams and spleens and peaked at 48 h. The maximum level of IFN-gamma could be detected in all three specimens, and the highest titer was shown in the spleens. Endogenous TNF production was suppressed by in vivo administration of anti-CD4 monoclonal antibody (MAb) or anti-asialo GM1 antibody but not by anti-CD8 MAb, whereas none of these antibodies suppressed endogenous IL-6 production. Endogenous production of neither IL-6 nor IFN-gamma was inhibited in rabbit anti-recombinant mouse TNF-alpha antibody-treated mice. Similarly, production of TNF and IL-6 did not decrease in anti-mouse IFN-gamma MAb-treated animals, but TNF production was augmented in these animals. These results suggest that the these endogenous cytokines are produced by different mechanisms in L. monocytogenes infection.

Endogenous gamma interferon-independent host resistance against Listeria monocytogenes infection in CD4+ T cell- and asialo GM1+ cell-depleted mice

The effects of in vivo administration of antibodies against T-cell subsets and asialo GM1 (ASGM1)-bearing cells on endogenous gamma interferon (IFN-gamma) production and host defense in Listeria monocytogenes-infected mice were investigated. Endogenous IFN-gamma titers in the bloodstreams and spleen extracts of mice on day 2 of infection were partially suppressed by administration of rabbit anti-ASGM1 antibody, but not by anti-CD4 monoclonal antibody (MAb) or anti-CD8 MAb. Of the different combinations of these three antibodies, the most suppressive effect on IFN-gamma production was observed after administration of anti-CD4 Mab and anti-ASGM1 antibody, although anti-CD8 MAb combined with anti-CD4 MAb partially inhibited IFN-gamma production. In contrast, antilisterial resistance was suppressed by the administration of anti-CD8 MAb but not by anti-CD4 MAb or anti-ASGM1 antibody. Antilisterial resistance in mice in which both CD4+ cells and ASGM1+ cells had been depleted was performed as efficiently as in normal mice in spite of the fact that endogenous IFN-gamma production was markedly suppressed. Furthermore, these mice also eliminated L. monocytogenes cells efficiently from the spleens even when they were pretreated with anti-mouse IFN-gamma MAb. These results indicate that CD4+ T cells, CD8+ T cells, and ASGM1+ cells are all responsible for endogenous IFN-gamma production and that antilisterial resistance and endogenous IFN-gamma production are not absolutely correlated.

Analysis of the time course of IFN-gamma mRNA and protein production during primary murine listeriosis. The immune phase of bacterial elimination is not temporally linked to IFN production in vivo.

IFN-gamma clearly plays an important role in the murine host response against Listeria monocytogenes, but the time course of its production and its precise role in immunity remain controversial. To address these issues, we sequentially monitored IFN production and bacterial accumulation in vivo in C57B1/6 mice during primary listeriosis. IFN-gamma mRNA levels (measured by Northern blot analysis of freshly isolated splenic RNA) and serum IFN (measured by ELISA) were both maximal on day 1 of infection, decreasing steadily after day 2 to barely detectable levels by days 4 to 6. Significantly, there was no direct relationship between IFN levels and listericidal activity in vivo. Between days 1 and 3, the period of maximal IFN production, host bacterial load (assessed by quantitating live L. monocytogenes/spleen) increased approximately 10- to 50-fold. On the other hand, during the immune phase of infection (between days 5 and 7), a period when both IFN mRNA and protein were barely detectable, the host bacterial load decreased 1,000- to 10,000-fold. The paucity of IFN production in vivo during the immune phase was unexpected in light of previous reports demonstrating abundant in vitro lymphokine release by splenocytes isolated during the same time period. By direct comparisons of IFN production in vivo and in vitro, however, we could show that the late (days 6-7) peak of IFN release observed in Ag-stimulated cultures was an in vitro artifact. By contrast the pattern of spontaneous IFN release (obtained when freshly isolated cells were incubated in the absence of Ag) conformed more closely to that observed in vivo. Because listerial Ag stimulated vigorous lymphokine release in vitro, we sought to determine whether an analogous effect could be observed in vivo. In fact, even the infusion of very large doses of live bacteria (5-20,000,000/mouse) did not stimulate endogenous IFN-gamma production in mice infected for 6 to 7 days. These studies suggest three major conclusions: 1) IFN production in vivo occurs primarily during the early phase of listeriosis; 2) the dramatic decrease in bacterial numbers observed late in infection cannot be directly attributed to increased IFN production by LM-immune T cells; 3) although Ag-driven cultures of freshly isolated cells can provide useful information about the potential lymphokine-producing capabilities of Ag-specific T cells, these results have limited relevance in understanding patterns of T cell lymphokine production in vivo.

EVALUATION OF CYTOKINES AND CYTOKINE-INDUCED SECONDARY MESSAGES IN SERA OF PATIENTS AFTER LIVER TRANSPLANTATION

The study objective was first to investigate serum levels of tumor necrosis factor alpha, interleukin 1 beta, interferon gamma, interferon alpha, interleukin 2, beta-2-microglobulin (B2M), and urinary neopterin in patients after orthotopic liver transplantation; and second to relate their levels to clinical complications. The design used was the prospective observation study, and the setting used was the transplant unit of a university medical center. Serum samples were collected from 20 patients every alternate day from transplantation until discharge. The measurements and main results were as follows: concentrations of cytokines, B2M, and neopterin were performed using commercially available radioimmuno-assays. In seven out of nine patients with acute cellular rejections, elevated levels of TNF-alpha, IFN-gamma, IL-1, B2M, and neopterin were detected. The highest absolute levels of TNF-alpha were observed in patients with CMV disease. Increments in bacterial infections were comparable to those seen in the above-mentioned groups with the exception of IFN-gamma, which remained stable. IL-1 serum levels showed a different pattern with peak concentrations measured in sera before transplant and during rejection, while in the case of CMV disease levels gradually decreased. No detectable levels of IFN-alpha or IL-2 were observed. Our results indicate that enhanced endogenous production of TNF-alpha and IFN-gamma accompanied by elevated levels of B2M and neopterin represent a regular feature of inflammatory complications after liver transplantation. Serum cytokine levels however were not useful in distinguishing between rejection and infection. Evaluation of neopterin was more sensitive than cytokine or B2M measurement for the detection of inflammatory complications.

Murine B cells expressing Thy-1 after in vivo immunization selectively secrete IgE.

IL-4 induces Thy-1 expression and IgE secretion by LPS--and T cell-stimulated murine B cells in vitro. IFN-gamma inhibits both of these IL-4-mediated effects. IL-4 and IFN-gamma are often exclusively produced by different CD4+ T cell subsets. Injection of mice with a polyclonal goat anti-mouse IgD antibody (GaM delta) stimulates large increases in the serum concentration of IgE through the production of IL-4. Neutralization of endogenous IFN-gamma production in GaM delta-injected mice leads to further increases in serum IgE levels. We show that IL-4 and IFN-gamma, produced after GaM delta injection, respectively, stimulate and inhibit the number of splenic B cells expressing Thy-1 in vivo. Increased numbers of Thy-1-expressing B cells are observed concomitantly with the onset of enhanced IgE secretion. These Thy-1-expressing B cells are highly and selectively enriched for IgE-secreting cells.