Acute Phase Of Viral Infection Research Articles

Analysis of the immune response and viral evolution during the acute phase of SIV infection

Development of an effective vaccine against human immunodeficiency virus (HIV) will require knowledge of the immune responses that correlate with protection. During the acute phase of HIV infection the host immune responses appear to control viral replication. It is thought that virus-specific cellular immunity is intimately involved in this viral control. We have developed a model system to measure the entire T cell response and viral evolution in the face of this onslaught in rhesus macaques during the acute phase of infection with molecularly cloned simian immunodeficiency virus (SIV). We used intracellular cytokine staining (ICS) of peripheral blood mononuclear cells (PBMCs) from animals during the acute phase of viral infection stimulated with peptides spanning the entire protein sequence of SIV to determine which peptides were recognized by CD8 and CD4 positive T cells. Furthermore, we sequenced the entire virus during the acute phase of infection. This approach has proved highly effective for measuring acute phase T cell responses and viral evolution in SIV-infected rhesus macaques and might facilitate the definition of cellular immune responses in HIV-infected humans during the acute phase.

Dominance of CD8 responses specific for epitopes bound by a single major histocompatibility complex class I molecule during the acute phase of viral infection.

Cytotoxic T-lymphocyte (CTL) responses are thought to control human immunodeficiency virus replication during the acute phase of infection. Understanding the CD8(+) T-cell immune responses early after infection may, therefore, be important to vaccine design. Analyzing these responses in humans is difficult since few patients are diagnosed during early infection. Additionally, patients are infected by a variety of viral subtypes, making it hard to design reagents to measure their acute-phase immune responses. Given the complexities in evaluating acute-phase CD8(+) responses in humans, we analyzed these important immune responses in rhesus macaques expressing a common rhesus macaque major histocompatibility complex class I molecule (Mamu-A*01) for which we had developed a variety of immunological assays. We infected eight Mamu-A*01-positive macaques and five Mamu-A*01-negative macaques with the molecularly cloned virus SIV(mac)239 and determined all of the simian immunodeficiency virus-specific CD8(+) T-cell responses against overlapping peptides spanning the entire virus. We also monitored the evolution of particular CD8(+) T-cell responses by tetramer staining of peripheral lymphocytes as well as lymph node cells in situ. In this first analysis of the entire CD8(+) immune response to autologous virus we show that between 2 and 12 responses are detected during the acute phase in each animal. CTL against the early proteins (Tat, Rev, and Nef) and against regulatory proteins Vif and Vpr dominated the acute phase. Interestingly, CD8(+) responses against Mamu-A*01-restricted epitopes Tat(28-35)SL8 and Gag(181-189)CM9 were immunodominant in the acute phase. After the acute phase, however, this pattern of reactivity changed, and the Mamu-A*01-restricted response against the Gag(181-189)CM9 epitope became dominant. In most of the Mamu-A*01-positive macaques tested, CTL responses against epitopes bound by Mamu-A*01 dominated the CD8(+) cellular immune response.

Hepatitis C virus core protein inhibits human T lymphocyte responses by a complement-dependent regulatory pathway.

Complement proteins are involved in early innate immune responses against pathogens and play a role in clearing circulating viral Ags from the blood of infected hosts. We have previously demonstrated that hepatitis C virus (HCV) core, the first protein to be expressed and circulating in the blood of infected individuals, inhibited human T cell proliferative response through interaction with the complement receptor, globular domain of C1q receptor (gC1qR). To investigate the mechanisms of HCV core/gC1qR-induced inhibition of T cell proliferation, we examined the effect of core protein on the early events in T cell activation. We found that HCV core inhibited phosphorylation of extracellular signal-regulated kinase (ERK) and mitogen-activated ERK kinase (MEK). HCV core-induced impairment of ERK/MEK mitogen-activated protein kinase resulted in the inhibition of IL-2 and IL-2Ralpha gene transcription, which led to the inhibition of IL-2 production and high-affinity IL-2R expression. Importantly, the ability of anti-gC1qR Ab treatment to reverse HCV core-induced inhibition of ERK/MEK phosphorylation reveals that the interaction between HCV core and gC1qR is linked to the interference of ERK/MEK mitogen-activated protein kinase activation. These results imply that HCV core-induced blockage of intracellular events in T cell activation by a complement-dependent regulatory pathway may play a critical role in the establishment of HCV persistence during the acute phase of viral infection.

Enhanced expression of cytokine genes in spleen macrophages during acute infection with infectious bursal disease virus in chickens

We examined the effects of infectious bursal disease virus (IBDV) on splenic T cells and macrophages. In acute IBDV infection, splenocytes responded poorly to Con A stimulation. However, when T cells were isolated from whole spleen cells, purified T cells responded normally to Con A. This result indicated that functional T cells were present in the spleen but mitogen-induced proliferation of T cells was being suppressed by other cells. Previous studies indicated that soluble factors from suppressor cells may mediate this inhibition of T cell mitogenesis. We thus examined the effects of IBDV on spleen adherent cells. Reverse transcriptase–polymerase chain reaction (RT–PCR) was used to quantitate the expression of several cytokine genes in splenic macrophages. In acute IBDV infection, splenic macrophages exhibited enhanced gene expression of type I interferon (IFN), chicken myelomonocytic growth factor (cMGF), an avian homolog of mammalian IL-6, and 9E3/CEF4, an avian homolog of mammalian IL-8. Mitogen-stimulated spleen cell cultures also produced elevated levels of nitric oxide. The elevation of cytokine gene expression by macrophages occurred transiently during the acute phase of viral infection and coincided with in vitro inhibition of T cell mitogenic response of spleen cells.

Enhancement of feline immunodeficiency virus (FIV) infection after DNA vaccination with the FIV envelope.

Despite intensive experimentation to develop effective and safe vaccines against the human immunodeficiency viruses and other pathogenic lentiviruses, it remains unclear whether an immune response that does not afford protection may, on the contrary, produce adverse effects. In the present study, the effect of genetic immunization with the env gene was examined in a natural animal model of lentivirus pathogenesis, infection of cats by the feline immunodeficiency virus (FIV). Three groups of seven cats were immunized by intramuscular transfer of plasmid DNAs expressing either the wild-type envelope or two envelopes bearing mutations in the principal immunodominant domain of the transmembrane glycoprotein. Upon homologous challenge, determination of plasma virus load showed that the acute phase of viral infection occurred earlier in the three groups of cats immunized with FIV envelopes than in the control cats. Genetic immunization, however, elicited low or undetectable levels of antibodies directed against envelope glycoproteins. These results suggest that immunization with the FIV env gene may result in enhancement of infection and that mechanisms unrelated to enhancing antibodies underlay the observed acceleration.

Enhanced responsiveness to nuclear factor kappa B contributes to the unique phenotype of simian immunodeficiency virus variant SIVsmmPBj14

Infection with a variant of simian immunodeficiency virus, SIVsmmPBj14, leads to severe acute disease in macaques. This study was designed to investigate the functional significance of previously described mutations in the viral long terminal repeat (LTR) and to elucidate their contribution to the unique phenotype of SIVsmmPBj14. LTR-directed transcription was measured by using luciferase reporter constructs that were transiently transfected into cultured cells. In a wide range of cell types, the basal transcriptional activity of the LTR from SIVsmmPBj14 was found to be 2- to 4.5-fold higher than that of an LTR from a non-acutely pathogenic strain. These LTRs differ by five point mutations and a 22-bp duplication in SIVsmmPBj14, which includes a nuclear factor kappa B (NF kappa B) site. Transcriptional differences between these LTRs were further enhanced by two- to threefold upon treatment of cells with phorbol ester or tumor necrosis factor alpha or by cotransfection with plasmids expressing NF kappa B subunits. Mutagenesis studies, and the use of a reporter construct containing an enhancerless promoter, indicate that these transcriptional effects are due principally to the 22-bp sequence duplication and the NF kappa B site contained within it. Finally, infectious virus stocks that were isogenic except for the LTR were generated. The LTR from SIVsmmPBj14 was found to confer an increase in the kinetics of virus replication in cultured cells. Inclusion of this LTR in recombinant SIVs also resulted in a two- to threefold rise in the extent of cellular proliferation that was induced in quiescent simian peripheral blood mononuclear cells. These studies are consistent with the hypothesis that LTR mutations assist SIVsmmPBj14 in responding efficiently to cellular stimulation and allow it to replicate to high titers during the acute phase of viral infection.

Viral illnesses and sports performance.

SummaryViruses are ubiquitous and cause numerous infections in humans. These may vary from asymptomatic infection to severe debilitating illness. Viruses enter the host cells to replicate, using host synthetic mechanisms, and, thus, are resistant to conventional antibiotics. The human body responds to viral infection by synthesising specific antibody which can be used to aid diagnosis. Infectious mononucleosis (glandular fever) commonly affects the 15 to 30 years age group. It may produce severe debility which may last a month or more. Coxsackie virus infection can produce symptoms of the common cold but may also invade heart muscle and produce myocarditis, a potentially serious disease. Other viruses also produce a wide spectrum of disease.Recent evidence has shown that people undergoing severe mental or physical stress may have reduced immunity to viral infections. There are risks associated with strenuous physical activity during the acute phase of viral infection, and there are reports of sudden death and serious complications occurring in previously fit young adults who undertake vigorous exercise when in the acute phase of a viral illness. Abnormalities of skeletal muscle have been demonstrated in patients with viral infection and this may explain the loss of performance experienced by athletes after upper respiratory tract infection.As a general rule, for all but mild common colds, it is advised that the athlete avoids hard training for the first month after infection.