Meet the Cells of the Immune System

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A couple of weeks ago I talked to you about my project. However, it was (rightly) pointed out that maybe I should introduce the parts of the project little by little. So let's start with the cells I work with.

First a quick introduction. Our immune system (IS) includes not only cells, but also tissues and molecules that allow the system to recognize and respond to disease from the common cold (a viral infection) to tuberculosis (a bacterial one). Now, the IS can be divided in two: the innate and the adaptive system. The first one, also known as the non-specific system, can be found pretty much on any animal. Plants and fungus also have similar innate system. However, only beginning with jawed fishes (unlike lampreys for example) and going to the rest of vertebrates, have what it's known as adaptive immune system. The main difference is that, as the name implies, the second one is capable of discriminating the type of ailment that the organism is encountering and respond accordingly, whereas the innate will just attack anything that is foreign. Another cool feature about the adaptive system is immune memory: it will remember encountering a certain type of infection and that is how next time you get a similar infection, your body will be able to respond faster and more efficiently.

Today I will only talk about the cells involved in the innate system, mainly because the cells that I work with are part of it. But if you guys are interested I will talk about the cells of the adaptive system later on. For now we are going to talk about Mast Cells, Natural Killer Cells, Granulocytes and the cells I work with, Phagocytes.

Mast Cells are mostly known for their roles in allergies. Yeap, these buddies produce histamine, a molecule that is involved in inflammation (which causes the inflammation of sinuses, hence the stuffy nose, watery eyes, etc). But don't be mad at them. This same inflammation is important to call more cells to the infection cells (more troops to respond!) and in this way regulate the response to the infection.

Natural Killer cells (NK) have a very appropriate name. They are ready to destroy cells that have been infected, when said cells cannot defend themselves. They also produce a molecule that serve as a calling signal for the macrophages to come fight!

Granulocytes receive their name because when seen with a microscope you can see tiny dots (granules) in them. There are divided in two main groups: basophil, with very low numbers and just like the mast cell, contains histamine hence also having a say in your allergic reactions and inflammation; and eosinophils, who play a big role in the elimination of worm infections, but they will also participate in allergies.

Finally the phagocytes, cells that eat or rather engulf. They can ingest other cells (a dying cell for example), parasites and particles. They all have the ability of extending their membranes, like a reaching hand, to grab their target and get it inside them. We mostly talk about 3 main phagocytes: Neutrophils, believed to be the one of the first cell types to arrive to an infection site and triggering the response; then we have dendritic cells (DC), this beautiful cells that look a bit like and octopus or a medusa with long "arms", their main role is to present fragments of whatever was engulfed (parasite or dying cell) to let other cells around what type of action should be taken; and last but not least "my" cell, the macrophage: now these fellas can internalize several parasites at a time, or large particles which is why they got the "macro" part. Once inside, the internalized item will be "digested" to be presented, just like I mentioned DC do. Together DC and macrophages are also known as Professional Antigen Presenting cells.

That ends our little introduction to innate immune cells. Please let me know in the comments if it was clear, if you want more information on each cell, or anything you feel like sharing really. Next week, we will talk about proteins!