Effects of interferon on the lymphocyte subset in the blood and lymphoid organs in mice

STAT2 Knockout Syrian Hamsters Support Enhanced Replication and Pathogenicity of Human Adenovirus, Revealing an Important Role of Type I Interferon Response in Viral Control

Human adenoviruses have been studied extensively in cell culture and have been a model for studies in molecular, cellular, and medical biology. However, much less is known about adenovirus replication and pathogenesis in vivo in a permissive host because of the lack of an adequate animal model. Presently, the most frequently used permissive immunocompetent animal model for human adenovirus infection is the Syrian hamster. Species C human adenoviruses replicate in these animals and cause pathology that is similar to that seen with humans. Here, we report findings with a new Syrian hamster strain in which the STAT2 gene was functionally knocked out by site-specific gene targeting. Adenovirus-infected STAT2 knockout hamsters demonstrated an accentuated pathology compared to the wild-type control animals, and the virus load in the organs of STAT2 knockout animals was 100- to 1000-fold higher than that in wild-type hamsters. Notably, the adaptive immune response to adenovirus is not adversely affected in STAT2 knockout hamsters, and surviving hamsters cleared the infection by 7 to 10 days post challenge. We show that the Type I interferon pathway is disrupted in these hamsters, revealing the critical role of interferon-stimulated genes in controlling adenovirus infection. This is the first study to report findings with a genetically modified Syrian hamster infected with a virus. Further, this is the first study to show that the Type I interferon pathway plays a role in inhibiting human adenovirus replication in a permissive animal model. Besides providing an insight into adenovirus infection in humans, our results are also interesting from the perspective of the animal model: STAT2 knockout Syrian hamster may also be an important animal model for studying other viral infections, including Ebola-, hanta-, and dengue viruses, where Type I interferon-mediated innate immunity prevents wild type hamsters from being effectively infected to be used as animal models.

Seven days of low-dose orally administered murine type I interferon does not cause priming in vivo

In vivo, low-dose orally administered type I interferon (LDOA IFN) therapy has been shown to provide beneficial effects in a number of diseases. These diseases vary in nature (viral, autoimmune, and neoplastic), yet LDOA IFN therapy is able to provide effective treatment. Despite the growing knowledge of the efficacy of such treatment and ongoing human clinical trials, the mechanism by which LDOA IFN acts remains largely unknown. In this study, we examined the phenomenon known as "priming" as a potential mechanism by which LDOA IFN effects may be mediated. Priming is a phenomenon in which pretreatment of cells or entire organisms with type I IFN causes significantly enhanced IFN production after induction of the endogenous IFN system by virus or polyI:C. This phenomenon of priming has been exploited in commercial industry for the mass production of type I IFN for medical and research use. It was found that LDOA IFN treatment did not cause priming in vivo.

Characterization of extrathymic T cells induced by recombinant murine interferon-beta in the peritoneal cavity of nude mice

The effects of recombinant murine interferon-beta (rMuIFN-beta) on extrathymic lymphocyte formation in the peritoneal cavity of BALB/c athymic nude mice and tumor-bearing nude mice were examined for comparison with BALB/c normal euthymic mice. The 7 days of administration of 1 x 10(5) IU rMuIFN-beta caused the number of these cells to increase remarkably in the peritoneal cavity as a unique subset of asialoGM1+CD4+CD8-TcR alpha beta+ T cells. The asialoGM1+CD4+ T cells produced IL-2 and IFN-gamma in primary culture without stimulant but did not proliferate. Thus, extrathymic T cells can be induced easily in the peritoneal cavity in addition to the thymus for host defense systems.

Changes in mononuclear peripheral blood cells in cattle with foot-and-mouth disease

The percentages and absolute numbers of mononuclear peripheral blood cells (MNC) were studied in vaccinated (Vac) and non-vaccinated (control) cattle, challenged with foot-and-mouth disease virus (FMDV). All Vac cattle but none of the controls resisted challenge. Cell populations were studied immediately before and one week after challenge, by direct and indirect immunofluorescence, using polyclonal and monoclonal antibodies against different bovine markers. Total B-lymphocytes, as assessed with polyclonal anti-IgG (H + L) antisera, as well as total mononuclear cells, were normal before and after infection, and did not change in Vac or control groups. Before challenge Vac cattle had higher numbers of ILA-29+ (a putative marker for null cells or, alternatively, for gamma delta T-cells) than control cattle. After challenge, in control cattle, the number of total T-cells, BoT4-bearing (helper) T-cells and BoT8-bearing (cytotoxic/suppressor) T-cells were decreased, while IgM-bearing B-lymphocytes, as well as monocyte/macrophage cells were increased. The number of IL-A29-bearing T-cells did not change after infection in either group. After challenge, Vac cattle also showed increased numbers of IgM-bearing B-lymphocytes and monocyte/macrophage cells, whereas T-subpopulations did not change significantly.

Inhibition of lymphocyte recirculation by murine interferon: effects of various interferon preparations and timing of administration

The effects of highly purified and/or recombinant interferon (IFN)-alpha/beta, IFN-alpha, IFN-beta, IFN-gamma, and the IFN-inducer, poly(I):poly(C), on the circulation of peripheral blood leukocytes (PBL) and thoracic duct lymphocytes (TDL) of (BALB/cJ x C57Bl/6J)F1 mice were examined. Although all IFN classes could depress significantly the number of circulating PBL and TDL when given at sufficient doses, IFN-alpha appeared to be the most potent. Phenotypic analysis of lymphocytes in the blood and lymph during the decrease induced by IFN suggests that IFN-alpha/beta and IFN-alpha preferentially decrease the Lyt-2+, or suppressor/cytotoxic, subset. Timing of IFN administration was found to be an important factor. Repeated administration of IFN-alpha/beta once a day for 3 days produced continuous suppression of the number of circulating PBL. Administration of either IFN-alpha/beta or IFN-gamma in the evening resulted in a longer and more extensive inhibition of PBL circulation than when IFN was administered in the morning. Our results suggest that the leukopenia observed in many patients undergoing IFN therapy may, in part, be attributed to decreased lymphocyte recirculation, and that the timing of IFN administration may be important in maximizing its therapeutic index.

Interferon-induced inhibition of lymphocyte circulation: lack of effect on humoral immune responses to T-dependent or T-independent antigens

We have previously demonstrated that interferon (IFN) transiently inhibits the number of recirculating thoracic duct lymphocytes (TDL), while other researchers have demonstrated similar decreases in lymphocytes in peripheral blood. In the present study we examined whether or not this decreased lymphocyte recirculation contributes to IFN's suppressive effects on antibody formation. Immunizing at varying times during the period of maximal decrease in lymphocyte recirculation, there are no significant differences in the number of plaque-forming cells (PFC) or antibody titers generated to either a T-dependent antigen, sheep erythrocytes (SRBC) or a T-independent antigen, Type III pneumococcal polysaccharide (SSS-III). These results suggest that: (i) the suppressive effects of IFN on antibody responses are not related to changes in lymphocyte recirculation and (ii) lymphocyte circulation is not required during the early phases of the humoral immune response to antigens.