Question

What are at least five ways that poxviruses use captured cellular genes to evade or disable the immune system?

Answer 1

Poxviruses are large DNA viruses which have enough genes to encode proteins not directly involved in replication.They often encode a repertoire of proteins involved in habitat formation and immune evasion.these proteins cover a wide range of activities reflecting the complexity of immune response that they counter in their host. The survival of virus depends on perfect strategies to conceal itself from immune system.

a)The term virokine is given to viral encoded proteins secreted from infected host cell. Virokines are powerful immune modulating proteins created by capturing and modifying genes responsible for regulating the host immune response.

b)Many cytokine ( IL-6,IL-10) and cytokine receptor (TNFR) homologs found to signficantly disrupt cytokine-signalling pathways which results in masking of the host immune system from viral infection.

c)Chemokine homologs and chemokine inhibitors were found to effect on leukocyte chemotaxis remarkably. thes virokines either help virus to evade immune detection by blocking the influx of leukocytes into area of infection or cause recruitment of leukocytes to increase the pool of new host cells to allow for better dissemination.

d)Chemokine inhibitors have been found to block the cellular influx into areas of infection. these virokines that block the innate immune system, complement system.They nnot only prevent formation of membrane attack complex (MAC) but also block complement cascade at multiple places upstream to block the formation of inflammatory factors.Thus it greatly reduces the migration of leukocytes into area of viral infection.

e)In poxviruses, some proteins act intracellularly such as serine proteinase inhibitors (serpins) help in immune modulation. These serpins alter the programmed cell death(PCD), apoptosis. By blocking the intracellular enzymes, these serpins are able to prevent TNF- and IFn-induced, as well as T-lymphocyte-mediated Fas-induced apoptosis.

By protecting the infected cell from PCD, the virus is able to replicate in high titers and continue host evasion and disable host immune response.