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Mystery Rays from Outer Space
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| “How to avoid influenza: Gargle Daily” |
Every virus that infects a vertebrate, has to be able to deal with the vertebrate immune system. The virus’s ancestors that infected vertebrates must have been able to deal with the vertebrate immune system. Those viruses that couldn’t handle an immune response are extinct.
Some of the ways viruses handle immunity, we don’t think of as really “specific”. Rapid replication, for example, has benefits for the virus that extend past just beating the immune system to the punch. But just about every virus, even the smallest ones, also have some form of specific immune evasion gene — some way of blocking, dodging, diverting, or confusing the immune system.
In spite of this nearly universal presence, we don’t really have a good grasp of precisely what viral immune evasion genes do, as far as supporting viral pathogenesis. (For that matter, it’s only for a handful of viruses that we really have much understanding of the pathogenesis in general.) Some viruses have a huge number of genes that are clearly immune evasion genes, others apparently only have one or two. Sometimes you can knock out an immune evasion gene and virtually destroy the virus’s ability to infect; sometimes the knockout only has a modest effect; sometimes there’s no effect at all, or it may even make the virus more, rather than less, virulent.
Viruses are so different from each other1 that there are probably few if any general rules for immune evasion. Still, we’re not even at a point yet where we have non-general rules, so the more we learn the more likely we are to see patterns.
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| Physicians expressing their thanks to influenza. Coloured etching attributed to Temple West, 1803. |
Influenza, of course, has its own set of immune evasion genes. The most important one is the NS1 gene.2 NS1 blocks the interferon pathway, and to the extent that we can generalize, it seems that blocking interferon is one of the most critical things any virus can do. Almost every virus has some way of meddling with the interferon pathways, whether by …