Although I am an omnivore, I must have dairy butter on my morning sandwich, otherwise I lose my appetite. Similarly, the Norwegian dulce de leche type spread “Hapå” is according the Nestlé advertisment an effective means to get the kids to eat their sandwiches.
The macrophages behave a bit in the same way. They eat everything, but it helps a lot if a bacterium is covered with “Hapå”. It then goes down a lot faster.
It is the antibodies, one of the immune system’s main weapons, which act as “Hapå” for the macrophages.
Antibodies are produced by B cells and are identical to the immune receptors of the B-cells, except that they are no longer attached to the cell membrane. Instead they are being released from the B cells and are distributed with the blood stream to the entire body.
An antibody may bind especially well to a particular bacterium. However, the first time a bacterium enters the body, generally there are not many antibodies present that can bind to the bacterium.
Still, there may be some B-cells that have a receptor that can bind. Binding to a bacterium stimulates the B cells to produce more antibodies, and actually over time also better antibodies (how it happens, I will come back to).
Therefore, the next time the same microbe emerge, the body will be well prepared. The bacteria are quickly covered with antibodies, macrophages get increased appetite and engulf the bacteria before they have been able to make much damage to the body. In a short time hopefully the bacteria have been defeated and the danger is over.
The macrophages enjoy bacteria with “Hapå” so much because they have some particular Fc receptors on their surface. These receptors bind to the antibodies that are attached to the bacteria. One could imagine these receptors almost like some kind of tentacles. The signals from these arms ensures that the macrophages finish their “sandwiches”.
So next time you want to trick your “Indian kids” into eating their lunch by the help of Hapå, why not offer to “opsonize” their toasts. For this is the term used for this phenomenon in relation to antibodies and macrophages.
Blogpost written by Anne Spurkland, 09/20/12
Translated from Norwegian 5th March 2016