Expression of Interleukin-4 by Recombinant Respiratory Syncytial Virus Is Associated with Accelerated Inflammation and a Nonfunctional Cytotoxic T-Lymphocyte Response following Primary Infection but Not following Challenge with Wild-Type Virus

Abstract

The outcome of a viral infection or of immunization with a vaccine can be influenced by the local cytokine environment. In studies of experimental vaccines against respiratory syncytial virus (RSV), an increased stimulation of Th2 (T helper 2) lymphocytes was associated with increased immunopathology upon subsequent RSV infection. For this study, we investigated the effect of increased local expression of the Th2 cytokine interleukin-4 (IL-4) from the genome of a recombinant RSV following primary infection and after a challenge with wild-type (wt) RSV. Mice infected with RSV/IL-4 exhibited an accelerated pulmonary inflammatory response compared to those infected with wt RSV, although the wt RSV group caught up by day 8. In the first few days postinfection, RSV/IL-4 was associated with a small but significant acceleration in the expansion of pulmonary T lymphocytes specific for an RSV CD8 ؉ cytotoxic T-lymphocyte (CTL) epitope presented as a major histocompatibility complex class I tetramer. However, by day 7 the response of tetramer-positive T lymphocytes in the wt RSV group caught up and exceeded that of the RSV/IL-4 group. At all times, the CTL response of the RSV/IL-4 group was deficient in the production of gamma interferon and was nonfunctional for in vitro cell killing. The accelerated inflammatory response coincided with an accelerated accumulation and activation of pulmonary dendritic cells early in infection, but thereafter the dendritic cells were deficient in the expression of B7-1, which governs the acquisition of cytolytic activity by CTL. Following a challenge with wt RSV, there was an increase in Th2 cytokines in the animals that had previously been infected with RSV/IL-4 compared to those previously infected with wt RSV, but the CD8 ؉ CTL response and the amount of pulmonary inflammation were not significantly different. Thus, a strong Th2 environment during primary pulmonary immunization with live RSV resulted in early inflammation and a largely nonfunctional primary CTL response but had a minimal effect on the secondary response.

Delivery of Cytokines by Recombinant Virus in Early Life Alters the Immune Response to Adult Lung Infection

“…A similar phenotype of reduced viral load was observed with a recombinant RSV that expresses IL-18; in this case, replication occurs normally in vitro but is reduced in vivo (17). It is possible that both RSV recombinants have impaired growth in vivo but that IL-4 expression leads to an impaired antiviral defense and enhanced viral replication that matches the impaired growth caused by gene insertion (6). However, the simplest explanation is that IFN-␥ expression decreased the viral load because it augments antiviral immunity.…”

“…RSV (strain A2) was obtained from the ATCC, and recombinant RSV expressing mouse IFN-␥ (RSV/IFN-␥) or IL-4 (RSV/IL-4) or wild-type recombinant virus (RSV/wt) was made as described previously (5,6). Time-mated pregnant BALB/c mice (Harlan, Iscoed, United Kingdom) were purchased at Ͻ14 days of gestation, and pups were weaned at 3 weeks of age.…”

“…These viruses grow in both human and mouse cell lines with kinetics similar to those of wild-type viruses (data not shown). In adult BALB/c mice, RSV/IL-4 grows at wild-type levels, while RSV/IFN-␥ is attenuated approximately 10-fold (5,6,16). To assess the effect of these viruses on neonates, mice less than 1 week of age were infected with 8 ϫ 10 4 FFU RSV/wt, RSV/IFN-␥, or RSV/IL-4 intranasally (i.n.).…”

“…In contrast, the coexpression of IL-4 by RSV (RSV/IL-4) causes defective T-cell responses but does not affect viral clearance (6). Upon challenge, RSV/IFN-␥-primed adult mice show enhanced CD8 T-cell recruitment, leading to immunopathology, while RSV/ IL-4-primed mice showed enhanced eosinophilia (16).…”

Interleukin 18 Coexpression during Respiratory Syncytial Virus Infection Results in Enhanced Disease Mediated by Natural Killer Cells

“…In the presence of IL-12, IL-18 is also capable of preventing IgE production (34), but in the absence of IL-12 (or with an abundance of IL-2 or IL-4), it promotes the differentiation of Th2 cells and induces nonspecific IgE production (33, 35). Increased RSV titers are seen in IL-18 knockout mice (2), and polymorphisms in the IL-18 promoter are associated with increased risk of severe bronchiolitis (23).To enhance and redirect immune responses upon RSV infection, we inserted various cytokine genes into the RSV genome for coexpression during infection in vitro and in vivo (3)(4)(5)(6)(7)13). In the present study, we used this technique to investigate whether the potent immune-modulating capacity of IL-18 could be used to boost virus-specific immunity as a vaccine candidate; in addition, we aimed to examine how IL-18 expression influenced lung immune responses and disease severity.…”