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-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.  

**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.

[[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]]

*[[Immunoglobulin|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)