Defence against viruses

Besides being explored as an antiviral tool, the crustacean RNAi machinery is now widely used for manipulating gene expression in crustaceans (see an overview by Hirono et al., 2011). Gene specific silencing is in most cases readily achieved by injecting dsRNA into to hemolymph and this technique has in a few years become an indispensable tool in crustacean research (Watthanasurorot et al. 2010). 

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Waterhouse, P.M., Wang, M.B., and Lough, T. (2001). Gene silencing as an adaptive defence against viruses. Nature 411 834-842. 

The complement system belongs to the non-specific humoral defence system. It plays an important part in antigen processing and is involved in the defence against viruses and tumors. Activation of complement leads to increased destruction and lysis of cells that possess a lipoprotein membrane, i.e. bacteria, viruses, and tumor cells. Conversely, complement is partly responsible for some inflammatory processes that occur in a state of hyper-reactivity and is able to eliminate immune aggregates. The complement system can be subdivided into the classical and alternative activation pathway. The classical pathway is dependent on antibodies (IgM and IgG), whereas the alternative pathway can be activated by microorganisms on their own or in combination with IgA antibodies. 

Two major advantages stem from the use of live vaccines. Firstly, the immunization mimics a natural infection such that only a single exposure is required to render an individual immune. Secondly, the exposure may be mediated through the natural route of infection (e.g. oral) thereby stimulating an immime response that is appropriate to a particular disease (e.g. secretory antibody as primary defence against poliomyelitis virus in the gut). 

Anti-viral drugs use mechanisms that interfere with nucleic acid and protein synthesis, inhibiting their attachment to and penetration of host cells. Because the viruses frequently adapt their structures, their elimination is difficult. A research team in Cambridge19 are looking at what they call a mutator protein . This protein is made by our own cells and is released to sneak inside certain viruses and cause chaos and mutations in their genome. Unfortunately the AIDS virus has evolved a defence against this process, but it is useful for other viruses. 

Murray, A. G. (1995). Phytoplankton exudation Exploitation of the microbial loop as a defence against algal viruses.Plankton Res. 17(5), 1079—1094. 

Interferons are a group of pleiotropic cytokines with important proinflammatory functions required in defence against infections with bacteria, viruses and multicellular parasites along with fundamental functions in other processes such as cancer immuno-surveiUance, immune homeostasis and immunosuppression [209]. IFNs are classified into type I and type II IFNs [210]. Type I IFNs comprise multiple alpha IFNs (IFN-a), and single IFN-, -e, -k, - and -oo subtypes, all encoded by different genes. Type IIIFN consists of a single IFN-y gene. 

Adaptive immunity provides a defence against some of the pathogens that avoid the innate immune system and can mount an attack against the evolving and ever changing characteristics of disease-causing organisms, e.g., different strains of bacteria and viruses, such as those that cause influenza. 

Another example concerns the potentiation of a virulence factor of vaccinia virus, the strain used for smallpox vaccinations.3 In this case a property (factor) of the virus was engineered to more effectively eliminate an essential component of the innate immune system, which acts as the first line of defence against an infection. 

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