You have probably read about the great discovery that spread over social media yesterday: that the brain is connected to the immune systems through small vessels and that white blood cells have been found in the brain. It implies that there may be a control system in place regarding our immune response that we have until now, known very little, or nothing about.
This is all very well, but what is the immune system really? …and what are those white blood-cells they are talking about in the article?
We live in a bacterial soup
We live in a soup of pathogens (bacteria, viruses etc…) and are so to speak, in a constant war against invaders. The body’s defenses can crudely be split into non-specific defenses such as our skin and the acid stomach-juice that kills off most germs we manage to gobble down. If the pathogens get past these defenses, they become greeted by the next line of soldiers.
We also have a more specific defense that is made up by so called white blood cells (and entourage). This part of the immune system is either innate (you were born with it) or you have to develop immunity. Immunity develops when you are exposed to a pathogen and your immune system learns how to respond. The second time around, the system directly recognizes the invader as a pathogen and you will not get sick or less sick, this time. This is the same way vaccinations (= immunizations) work. It is like a school for the immune system.
What type of defenses do we have?
There are several types of white blood cells, all with different functions: lymphocytes (form antibodies), neutrophils (engulf and destroy bacteria and fungi – your first line of defense), basophils (small cells that chemically communicate with the rest of the system. They also secrete histamines, a response that has gotten out of hand during allergic reactions), monocytes (live the longest and break down bacteria) and eosinophils (these cells can also attack parasites and cancer cells).
The lymphocytes are formed in the bone-marrow and can be B- or T-cells. The T-cells mature in the thymus, which is a very important immune-system organ, as it is here many white blood cells learns how to differentiate between the body’s own cells and invaders. The B-cells mature in the bone marrow. It is these cells that are the reason that we can develop immunity and why vaccines work so fabulously well. I will dedicate another post to explaining antibodies and how vaccines work.
If inflammation occurs, the chemicals produced at the site will attract monocytes and neutrophils that are prepared to fight against a bacterial invasion. Hence, swelling is a necessary bodily response, but not good if it gets out of hand.
The lymphatic system
The lymphatic system is a curious thing: it is a network of lymph-vessels throughout the body, interconnected through lymph nodes that act as a filter of the lymph. Otherwise, infected lymph would spread throughout the body. There are as much as 600 lymph nodes in the body localized to sites like the armpit, the groin and the neck. I bet you have felt swollen lumps in your neck at some point when you had a terrible throat-ache. The swelling of the nodes is due to an accumulation of lymphatic cells ready for war.
There are many other organs involved in the immune system, the spleen for example, which is a sort of filtering system for the blood in regard to pathogens.
You see now how incredibly it is that a vessel system has been found connecting the brain directly to this complex system in another way than just though nerves. The implications of this are great as it may help us understand some brain-related illnesses that may be of an autoimmune nature i.e. when the body starts to fight itself (for example during MS). It might also aid a targeted transport of therapies to the brain.
One last comment: It has long been known that smoking, extreme exercise (or too little exercise) and stress may increase the white blood cell count and putting an unnecessary stress on the body, which can lower your tolerance for other illnesses. Hence, if you want to get more resistant to pathogens: stop smoking, exercise moderately and relax.
Dr. Anna of The Imaginarium
Immunobiology, 5th edition: The Immune System in Health and Disease. Charles A Janeway, Jr, Paul Travers, Mark Walport, and Mark J Shlomchik. New York: Garland Science; 2001. ISBN-10: 0-8153-3642-X