Physiological mechanisms of production and action of interferons in response to viral infections

Pharmacokinetics and pharmacodynamics of IFN-beta 1a in healthy volunteers

The pharmacokinetics of recombinant human interferon-beta1a (IFN-beta1a) (Rebif, Ares-Serono, Geneva, Switzerland) were investigated in healthy volunteers following intravenous (i.v.) administration of increasing single doses of the drug (22 microg/6 million international units [MIU], 44 microg/12 MIU, and 66 microg/18 MIU); i.v., intramuscular (i.m.), and subcutaneous (s.c.) administration of a 66-microg dose; and repeated s.c. administration of four 66-microg doses at 48-h intervals. The disposition of IFN-beta1a followed triexponential decay after i.v. administration (half-lives 3 min, 42 min, and 22 h, respectively). After s.c. and i. m. administration, absorption was the rate-limiting factor in the terminal phase. The median absolute bioavailabilities were 30% and 27%, respectively. The accumulation ratio after repeated s.c. injections was 2.4, and a terminal half-life of 66 h was observed. Intracellular 2-5A synthetase activity and serum neopterin and beta2-microglobulin concentrations increased after all IFN-beta1a injections and remained elevated following every-other-day administration. The local tolerance was good, and the systemic tolerance was satisfactory.

Genetic differences in the age-associated decrease in inducibility of natural killer cells by interferon-alpha/beta

Natural killer (NK) cells, which are important in viral infections and anti-tumor activity, show reduced cytotoxicity in aged mice. The mechanism(s) for this age-related decline in NK activity has not been clearly established. We assessed changes in NK cytotoxicity in splenocytes and peripheral blood mononuclear cells after interferon (IFN)-alpha/beta stimulation in adult (6 months) and aged (22-26 months) C57Bl/6, Balb/c, and (Balb/c x C57Bl/6)F1 mice. Aged C57Bl/6 and Balb/c mice had a significantly reduced IFN-alpha/beta-stimulated NK cytotoxicity compared to adult mice. In contrast, adult and aged F1 mice showed similar NK cytotoxicity after IFN-alpha/beta induction. The decreased ability of NK cells of aged mice to respond to induction by IFN-alpha/beta was not due to a requirement for an increased amount of IFN or for a longer period of treatment with IFN. Further, this decreased response did not appear to be the result of suppressive activity of adherent cells or T cells. While the percentage of NK cells (NK1.1+) was similar in adult and aged mice, the (CD8+ NK1.1+) subset of NK cells was significantly increased in aged mice. Importantly, the percentage of CD8+ NK1.1+ cells was inversely related to the cytotoxicity observed after IFN-alpha/beta treatment.

Endotoxin induces increased intracellular cathepsin B activity in THP-1 cells

Macrophage cathepsin B (CB) is implicated in tissue injury in inflammatory diseases. Lipopolysaccharide (LPS) is an activator of macrophages whose effect on CB is unknown. This study was undertaken to investigate the potential of macrophages as a source of increased CB and to determine if exposure to LPS might stimulate CB levels. As a model we chose the macrophage-like tumor line, THP-1. Incubation with LPS led to a time and dose-dependent increase in CB activity. LPS potentiated interferon-gamma (IFN-gamma)-induced elevations of CB and led to an additive increase in CB activity. Pretreatment of the cells with LPS not only caused a marked stimulation of CB activity over that seen with IFN-gamma alone, but also decreased the concentration and exposure time to the cytokine necessary to achieve maximum induction of the enzyme. The LPS and IFN-gamma induced CB increases were abolished by cycloheximide or actinomycin D in the cultures, indicating that the increases in CB required increased RNA transcription and de novo protein synthesis. Direct measurement of CB mRNA showed increases. These data indicate that although LPS alone appears to induce the production of CB in THP-1 cells, it augments IFN-gamma induced increases, suggesting that two signals are necessary for maximum CB induction in this system.

Interferon-gamma induced increases in intracellular cathepsin B activity in THP-1 cells are dependent on RNA transcription

Interferon-gamma (IFN-gamma) treatment of human macrophages induces increased intracellular levels of cathepsin B (CB), a lysosomal cysteine proteinase which is implicated in inflammatory tissue injury. To determine the mechanism of the increase, we studied the macrophage-like cell line, THP-1. Dose and time dependent increases in intracellular CB were seen when cells primed with phorbol ester (PMA) were cultured with IFN-gamma. To determine whether protein synthesis was required for the increase, PMA primed cells were cultured in the presence of IFN-gamma and cycloheximide: The expected increase was inhibited. To determine whether RNA synthesis was required for the IFN-gamma induced increases, PMA primed cells were cultured in the presence of IFN-gamma and actinomycin D. Again the expected increases were not seen. Direct measurement of CB mRNA levels showed increases in cells not treated with inhibitors. These results suggest that the IFN-gamma induced increases in THP-1 cell CB are dependent on RNA and protein synthesis.

Autoantibodies before, during and after administration of recombinant interferon-alpha for chronic viral hepatitis

This study was undertaken to investigate the presence of autoantibodies in patients with chronic viral hepatitis B and C, before, during and after interferon-alpha (IFN-alpha) therapy and to study their relation to dose and type of IFN-alpha and response to treatment. Fifty patients with chronic hepatitis were divided in two groups, a control-group of 21 patients (10 type B and 11 type C) who were followed for 6 months without treatment and an IFN-group consisting of 29 patients (8 type B and 21 type C) who received IFN therapy for 6 months. Serum samples were tested for a range of antibodies at the start of the study, during therapy and at the end of the 6 month period. Antibodies tested for included: antinuclear, smooth muscle, antimitochondrial, parietal cell and thyroid microsomal. Four (8%) of the total patient group had autoantibodies at the beginning of the study (two in each group). During the follow-up period no patient in the control group developed antibodies compared with 3 (11%) patients in the treatment group. Autoantibodies developed in patients treated with higher doses of IFN and were found in those patients who tended to show a poor response to IFN-therapy. Further studies are needed to establish the relationship between poor response to IFN-alpha and development of autoantibodies.

The interferons: a biological system with therapeutic potential in viral infections

Successful medical use of interferon for chronic viral infections is increasingly dependent on understanding the biologic and molecular mechanisms of the interferon system. Interferon (IFN) is one of the body's natural defenses. Production of IFN is a defensive response to foreign components of microbes, tumors and antigens. This IFN response begins with the production of the IFN proteins (alpha, beta and gamma) which then induce antiviral, antimicrobial, antitumor, and immunomodulatory actions. Thus, the initial production or administration of IFN(s) does not protect directly but instead reacts with specific receptors on cell surfaces to activate cytoplasmic transduction signals that then enter the nucleus to stimulate cellular genes encoding a number of effector proteins which lead to the defensive actions. The known molecular, humoral and cellular mechanisms by which these effector proteins exert their antiviral activities are presented. In addition, the pathogenesis of chronic infections is overviewed in the context of the interferon defenses.

Resistance of lymphocytic choriomeningitis virus to alpha/beta interferon and to gamma interferon

The susceptibility to alpha/beta interferon (IFN-alpha/beta) or to gamma interferon (IFN-gamma) of various lymphocytic choriomeningitis virus (LCMV) strains was evaluated in C57BL/6 mice and in various cell lines. Anti-IFN-gamma treatment in vivo revealed that the LCMV strains Armstrong, Aggressive, and WE were most susceptible to IFN-gamma whereas Traub, Cl 13-Armstrong, and Docile were resistant. The same pattern of susceptibility to recombinant IFN-gamma was observed in vitro. In vivo treatment with anti-IFN-alpha/beta showed a sizeable increase in replication of Aggressive, Armstrong, and WE; effects were less pronounced for Docile, Cl 13-Armstrong, or Traub. Correspondingly, WE, Armstrong, and Aggressive were all relatively sensitive to purified IFN-alpha/beta in vitro, and Cl 13-Armstrong, Docile, and Traub were more resistant. Overall, there was a good correlation between the capacity of LCMV strains to establish a persistent infection in adult immunocompetent mice and their relative resistance to IFN-gamma and IFN-alpha/beta.