health

Scientists look beyond antibodies in virus immunity hunt

5 Comments
By Paul RICARD

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© 2020 AFP

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No, because almost all people have had common cold and flu in their lives, yet some are reacting to coronavirus badly as if they had zero immunity to it.

That is irrelevant, the results from experiments show that only some people have cross reactivity of the T cells against covid19 antigens, that means the cells recognize the virus and put forward an immune response but only of those people. If your explanation were true then every single person would have that reaction because everybody has had colds (influenza has absolutely no role here), but this does not happen.

The reality is that not everybody gets sick from the same strains of viruses, and some of those strains can have antigens much closer to covid19 than others, cross neutralization is not a on/off thing but something that happens by degrees, this explains much better why some people have very high levels of viruses in the tissues, but never get more than a mild disease, or no disease at all.

It's something else, like how active ACE2 receptors are in human cells. Some have very active ACE2 receptors in large quantity ready to bond with COVID19 virus, while others do not or have the ACE2 receptor functionality disabled by enzymes.

ACE2 receptors fulfill no role on the reactivity of memory T cells, so once again this misunderstood explanation does not explain the differences. It also fails to explain how the receptor expression values are not correlated with disease severity (two people with approximately same ACE2 expression but wildly different disease).

You are confused between factors that modify virus replication and factors that modify the immune response against the infection, they are not the same thing.

3 ( +3 / -0 )

Current T-cells in most humans have no memory of this COVID19. They only start producing immune response after being exposed to COVID19 coronavirus in a few days.

No, that only means you have not understood the article at all. The results of the study prove that even if the person have never been exposed to covid19 sometimes the T cells produce an immune response as soon as they are in contact with the virus. Not in a few days, immediately after being exposed.

That means that the cells are able to recognize covid19 as a pathogen by a phenomenon called cross-reactivity, this happens because other coronaviruses share parts of the proteins of the virus, so when the person was infected by those other coronaviruses (common colds) their cells "learned" to recognize these proteins and use this to also recognize covid19. The study points towards those other common cold coronaviruses acting like a natural vaccine that allows for some people to respond very quickly to the infection, as if they had it before.

Your explanation about ACE2 receptors is irrelevant for this. As I explained before, it is perfectly possible to examine how much of the receptor are being expressed on the cells, but this does not explain cases where two people have approximately the same levels but one have extremely serious complications while the other is completely asymptomatic. The explanation for this can be the cross-reactivity of their T-cells, one person having it while the other don't.

3 ( +3 / -0 )

A very complex virus. As with many other viruses, such as the poliovirus, most people either show no symptoms or are only mildly ill. But also as with many other viruses, a significant percentage of infected suffer horribly and die. This is not a virus that it is wise to ignore.

2 ( +2 / -0 )

@virusrex

Let me explain.

Current T-cells in most humans have no memory of this COVID19. They only start producing immune response after being exposed to COVID19 coronavirus in a few days.

In the meanwhile, the severity of COVID19 infection depends on ACE2 receptor quantity and quality. Some people have lots of ACE2 receptors on their cells that have not been blocked off by enzymes, so these people will produce severe COVID19 infections, while people with fewer ACE2 receptors or whose ACE2 receptors have been blocked off by enzymes will produce mild infections.

-2 ( +0 / -2 )

One hypothesis is that these T cells might help give people a level of cross-immunity protection from COVID-19 because they "remember" previous infections by other viruses in the same family, four of which cause common colds.

No, because almost all people have had common cold and flu in their lives, yet some are reacting to coronavirus badly as if they had zero immunity to it.

It's something else, like how active ACE2 receptors are in human cells. Some have very active ACE2 receptors in large quantity ready to bond with COVID19 virus, while others do not or have the ACE2 receptor functionality disabled by enzymes.

-3 ( +0 / -3 )

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