Infection & Immunity Group
Ongoing Research Areas
Nitric oxide and immunopathology
| Interferon-inducible chemokines in virus
clearance | Cytokines, cell-mediated immunity
and resistance to disease | Cytokines, cytotoxic
T lymphocytes and antibody in antiviral immunity | The
innate immune response in antiviral immunity | Role
of Membrane TNF in host response to virus infection | Genetic
Control of Early Immune Responses to Poxviruses and Herpesviruses
Nitric oxide and immunopathology
We have studied the antiviral role of nitric oxide (NO) using nitric oxide
synthase (NOS) inhibitors and NOS2 deficient mice. In addition, we are
currently investigating the role of NOS2 and NO in influenza pneumonia.
Intriguingly, we have found that NO has no antiviral activity in this
virus model and that virus clearance occurred via other interferon (IFN)-gamma-mediated
pathways. This work demonstrates for the first time, 1) the definitive
role of NO in the generation of viral immunopathology, and 2) the existence
of a novel IFN-gamma-mediated antiviral pathway in NOS2 GKO mice not obvious
in wildtype animals.
Interferon-inducible chemokines in virus
clearance
IFN-gamma mediates its antiviral effects through the induction of a number
of proteins. We have looked at two IFN-inducible chemokines, namely Mig
and Crg-2, and found that they are prominently upregulated during infection
of mice with vaccinia virus (VV). This led us to speculate that Mig and
Crg-2 may, infact, mediate some of the antiviral effects of IFNs. Using
the recombinant VV approach, we have now shown that Mig and Crg-2 mediate
antiviral activity in vivo through the rapid activation and recruitment
of NK cells and T lymphocytes to the site of virus replication. Indeed,
this is the first study that has established a role for these chemokines
in antiviral immunity.
Cytokines, cell-mediated immunity and resistance
to disease
Some strains of mice (e.g. C57BL/6) are genetically resistant, while others
(e.g. BALB/c and A/J) are genetically susceptible, to mousepox. We were
interested in determining whether or not these differences in disease
susceptiblity correlated in vivo with cytokine profiles and cell-mediated
immune responses. We have shown that resistance is associated with the
capacity of mice to produce the type 1 cytokines IL-2, IFN-gamma , IL-12
and TNF-alpha and to generate a potent CTL response early after infection.
The type 2 cytokine, IL-4, is produced by both resistant and susceptible
mice. Further, the cytokine response is compartmentalised; there are clear
differences in the cytokines that are produced in the lymph node (priming
site) compared with the spleen (effector site). These studies indicate
that susceptibilty to mousepox is associated with the lack of type 1 cytokine
synthesis and a delayed cell-mediated immune response.
Cytokines, cytotoxic T lymphocytes and antibody
in antiviral immunity
We remain interested in determining the in vivo effector function
of CD8 T lymphocytes that is critical for virus clearance. There is still
some question of whether it is their cytolytic potential or their ability
to produce cytokines which is important. Indeed, it has been proposed
that recovery from infection with cytopathic viruses requires cytokines
like IFN-gamma or antibody but not CTL whereas non-cytopathic viruses
require CTL but not antibody or cytokines. Our investigations using ectromelia
virus (EV), a cytopathic virus, indicate that recovery from a primary
infection with this virus clearly requires CTL (perforin-mediated cytolysis),
IFNs (IFN-alpha , -beta and -gamma ), and most intriguingly, antibody.
In addressing the role of these immune parameters in recovery from a secondary
EV infection, we have found that only antibody is critical for protective
immunity. Our data show that the requirement for cell-mediated immunity,
cytokines and antibody for recovery from a primary viral infection is
unrelated to whether the virus is cytopathic or non-cytopathic. However,
it may be related to virulence, replication properties or mode of spread
of the virus within the host.
The innate immune response in antiviral immunity
We are also interested in the link between innate and adaptive immune
responses to viral infections. Components, such as neutrophils, not only
provide the first line of defence, but also have the ability to profoundly
influence and direct the adaptive immune response. In addition, we are
also studying the role of B cells and antibody in the control of virus
replication in a primary infection.
Role of Membrane TNF in host response to virus
infection
One unique aspect of this study involves the assessment of the membrane
form of this cytokine in vivo, during the host immune response
to a replicating infectious pathogen. The initial studies in TNF gene
knockout mice have been promising and we are in the process of extending
these to utilize the recently developed membrane TNF knockin mouse (Jon
Sedgwick, DNAX, USA).
Genetic Control of Early Immune Responses
to Poxviruses and Herpesviruses
Cmv1 controls replication of murine cytomegalovirus (MCMV) in the
spleen via regulation of NK cells. This gene is linked to a region on
the mouse chromosome 6 designated Natural killer complex (NKC). One of
3 known genes that confer resistance to mousepox (designated Rmp1)
is also linked to the NKC region and Cmv1. The B6 mouse is resistant
to MCMV and ectromelia virus (the causative agent of mousepox) infections
whereas the BALB/c mouse is susceptible to both. Dr. A.A. Scalzo (UWA)
has generated BALB/c congenic mice with B6 NKC (BALB/C.Cmv1r) and several
intra-NKC recombinants. He has also established a colony of B6 congenic
mice with the BALB/c NKC. These congenic mice are unique tools and are
not available elsewhere. The purpose of this study is to establish (i)
whether Cmv1 also confers resistance against mousepox, (ii) whether
Rmp1 and Cmv1 are the same gene, and (iii) the mechanism(s)
through which Cmv1 and/or Rmp1 regulate NK cell activity
and confer resistance.
