Viruses have a secret, altruistic life
Quanta magazine released an article detailing the research performed by Rafael Sanjuan, a geneticist at the University of Valencia, who was conducting experiments to examine the behaviour of viral cells. The study uncovered that viral cells can interact socially with each other which can lead to “cooperation and conflict”. It refers to how some VSV virus cells (a virus related to rabies) stimulate an anti-reproductive protein known as interferons from the host which disrupts viral reproduction. However, these viral cells have adapted and they can survive these conditions of suppression (“altruists”) unless a “cheater” cell comes along. A cheater essentially reaps the rewards of the “altruistic” cells by being able to multiply more rapidly and attacking the host more vigorously despite being more susceptible to interferons. This enables the cheater cell to outcompete other types of virus cells as the altruistic cells effectively occupy the host’s defences long enough to allow for the reproduction of “cheaters”. Later in the article, Sanjuan’s research also discusses how viruses choose to attack in a cluster and overwhelm the immune responses of the host rather than diffusing and attacking multiple cells.
I believe we can begin to model and predict the different virus cells behaviour using game theory according to what types have cells have infected the body. First, we must bear in mind that the cells are working together and not against each other in their objective of trying to infect the host.
Let’s have player 1 as the “altruist” and player 2 as the “cheater”. The choices are attack and sacrifice in the game.
If the altruistic cell chooses to attack it might have a chance of survival but it will not suppress the interferons of the host making way for the reproduction of a cheater so the payoff is small.
If the altruistic cell sacrifices then it suppresses interferons and enables the cheater to reproduce and survive potentially enabling it to cluster and cause a more serious infection. A higher payoff.
If the cheater cell sacrifices it will be killed and the altruistic cells have a small chance of survival because they suppressed by interferons, so a low payoff.
If the cheater cell attacks, the altruistic cells will suppress the interferons and the infection has a greater chance of surviving and replicating, so a higher payoff.
If both sacrifice then the virus is not aggressive and the body has time to destroy the virus. Low Payoff
If both attack then the cheater will be destroyed first and the altruists are able to resist for a while until also destroyed. medium payoff
With this basic model of game theory, we can predict that altruistic cells will sacrifice and cheaters will attack because this is the combination that leads to the highest chance of successful infection. It is always best for altruists to sacrifice otherwise cheaters will be destroyed and altruists will struggle to reproduce. If cheaters sacrifice the same problem exists. Therefore the Nash Equilibrium can be defined as (sacrifice, attack) when the virus’s objective is to collaborate in a way to make the virus as aggressive as it can possibly be.
https://www.quantamagazine.org/viruses-have-a-secret-altruistic-social-life-20190415/
Good analysis.