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.

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

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

*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 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]]

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

*T cells

*[[T 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.

**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]]