One of the cosiest things I like to do before Christmas is to make pomander balls. Their smell of cloves and orange is so pleasant. They are easy to make, also for those with less well-developed fine motor skills. In addition, the orange balls with brown dots looks lovely, hanging in the window frame. In fact, they have some resemblance to virus particles.
Virus consist of a shell built by one or a few different proteins, which is reused repeatedly, just like the cloves piercing the orange skin. Hidden within the shell is the virus’ genetic material. By binding to the surface of a body cell, the virus can empty its genes into the cell, and thus get more virus particles produced.
Even if the killer cells of the immune system can detect and remove virus-infected body-cells, it is also important if possible, to stop the virus from penetrating into the body-cells in the first place. The task is not trivial, since it is not known how the virus will look like. It is simply a sea of possible virus-proteins that we need to defend ourselves against.
It is here that the immune system’s lottery reveals its real genius. By randomly combining a few gene motives in many different ways, the body is equipped with several million B cells that each has a defined receptor. Some few of these B cells have receptors that bind to the “cloves” in a given virus particle. B cells that has bound to a virus, will be stimulated to divide and after a while produce receptors that are secreted into the blood. These free receptors are called antibodies. The “cloves” that the antibody may bind to are called “antigens”.
Now comes a point that I find particularly intriguing. Antibodies consist of two identical arms that can bind antigens. The arms are bound together by a common part, which largely is identical for all antibodies. When an antibody binds to a viral particle, each of the two arms may bind to two “cloves” on the same virus. Equally likely is it that one of the arms of an antibody binds to one virus particle and the other arm binds to another virus particle. In this way a large “lump” of virus particles and antibodies may be formed. The virus particles are neutralized, and can no longer infect the body cells. And since the entire lump is covered by antibodies, can it be recognized and eaten by macrophages.
And voila, the virus is nearly eliminated. The few that slips away and nevertheless infect the body cells will be taken care of by the killer cells.
Just like the killer cells, it takes unfortunately several days before the B cells have managed to divide and make sufficient antibodies to eliminate an invading virus. So the first time one is infected with a given virus, one may get quite sick before the immune system gets to control the situation. Next time the same virus returns, will we have both antibodies and killer cells ready. Often times we therefore do not notice what we have been infected again, that quickly is the virus eliminated.
Blogpost by Anne Spurkland, published 9th November 2018
Originally published in Norwegian 20th October 2012