Changes

==Innate immunity==

==Innate immunity==

This becomes active during the early stages of infection. Defences include:

This becomes active during the early stages of infection. Defences include:

*Interferon (IFN)- typically stimulates the inhibition of viral replication. There are three known types:

*[[Cytokines|Interferon (IFN)]] - typically stimulates the inhibition of viral replication. There are three known types:

**Infection of a cell by a virus stimulates production of IFN-alpha and IFN-beta, which activate genes in neighbouring cells. One of these genes, for example, codes for a protein kinase that blocks translation of proteins. Another activates an endonuclease that degrades viral RNA.  

**Infection of a cell by a virus stimulates production of IFN-α and IFN-β, which activate genes in neighbouring cells. One of these genes, for example, codes for a protein kinase that blocks translation of proteins. Another activates an endonuclease that degrades viral RNA.  

**IFN-γ increases the expression of MHC I and II, enhancing the function of the adaptive immune response. It also activates macrophages and NK cells.

**IFN-γ increases the expression of MHC I and II, enhancing the function of the adaptive immune response. It also activates macrophages and NK cells.

*Natural killer (NK) cells- one of the main mediators of antibody-dependent cell-mediated cytotoxicity

*[[Natural Killer cells|Natural killer (NK) cells]] - one of the main mediators of antibody-dependent cell-mediated cytotoxicity

*For more on [[Innate Immunity to Viruses|Innate immunity to viruses]], see here.

*For more on [[Innate Immunity to Viruses|Innate immunity to viruses]], see here.

==Adaptive immunity==

==Adaptive immunity==

The importance of the adaptive immune system in responding to viral infections can be demonstrated using athymic 'nude' mice, which lack mature T cells. These mice show particular vulnerability to the herpes simplex virus, resulting in death when infection reaches the CNS. However transfer of antigen-specific T cells to the mice shortly after infection leads to recovery.

The importance of the adaptive immune system in responding to viral infections can be demonstrated using athymic 'nude' mice, which lack mature T cells. These mice show particular vulnerability to the herpes simplex virus, resulting in death when infection reaches the CNS. However transfer of antigen-specific T cells to the mice shortly after infection leads to recovery.

*Antibodies- these are particularly important in preventing the spread of the virus in the bloodstream

*[[Immunoglobulins|Antibodies]] - these are particularly important in preventing the spread of the virus in the bloodstream

**[[IgA]] production is increased at mucosal surfaces- helps prevent reinfection

**[[IgA]] production is increased at mucosal surfaces- helps prevent reinfection

**Although antibodies that target any viral protein can be produced, only those directed against proteins found in the virion envelope or infected cell membrane will be effective

**Although antibodies that target any viral protein can be produced, only those directed against proteins found in the virion envelope or infected cell membrane will be effective

**When targeted against free virus particles, antibodies are effective at preventing them binding and entering the cell and uncoating.

**When targeted against free virus particles, antibodies are effective at preventing them binding and entering the cell and uncoating.

**When targeting virus-infected cells, they aid antibody-dependent cell-mediated cytotoxicity by NK cells, macrophages and [[Neutrophils|neutrophils]]

**When targeting virus-infected cells, they aid antibody-dependent cell-mediated cytotoxicity by NK cells, [[Macrophages|macrophages]] and [[Neutrophils|neutrophils]]

*Complement- although not considered a major factor in defence against viruses, complement is able to damage the virion envelope (virolysis)

*[[Complement]] - although not considered a major factor in defence against viruses, complement is able to damage the virion envelope (virolysis)

**Coupled with antibody, complement is also able to:

**Coupled with antibody, complement is also able to:

***block the virus receptor

***block the virus receptor

***aid lysis of infected cells

***aid lysis of infected cells

***aid opsonisation of free virus or infected cells for phagocytosis

***aid opsonisation of free virus or infected cells for phagocytosis

 

[[Image:T Cell viral response.jpg|thumb|right|200px|T Cell Immunity to Viruses - B. Catchpole, RVC 2008]]

*[[T cells]]

[[Image:T Cell viral response.jpg|thumb|right|150px|T Cell Immunity to Viruses - B. Catchpole, RVC 2008]]

**CD8⁺ cytotoxic T cells are particularly important as nearly all the cells in the body express MHC class I. They tend to focus at the site of viral replication and destroy virus-infected cells.

**CD8+ cytotoxic T cells are particularly important as nearly all the cells in the body express MHC class I. They tend to focus at the site of viral replication and destroy virus-infected cells.

**CD4⁺ T cells are important in the recruitment of macrophages, using cytokines such as IFN-γ and TNF, and the induction of CD8⁺ cytotoxic T cells

**CD4+ T cells are important in the recruitment of macrophages, using cytokines such as IFN-γ and TNF, and the induction of CD8+ cytotoxic T cells

**The presence of CD4⁺ T cells is also vital for the antibody response, i.e. class-switching and affinity development

**The presence of CD4+ T cells is also vital for the antibody response, i.e. class-switching and affinity development

*For more on the adaptive response to viruses, see [[Adaptive Immunity to Viruses]]

*For more on the adaptive response to viruses, see [[Adaptive Immunity to Viruses]]