Immune System

Immune System

What is it?

Your immune system is what protects your body from germs, or pathogens, and has components ranging from skin to highly specialized leukocytes.

How does it work?

The 3 Lines of Defense

Line 1: Skin, Mucous, Stomach Acid, Saliva

The organs and fluids should be relatively familiar. Their job is to keep pathogens (disease causing agents) from entering your body.

Pathogens can include foreign: Proteins, Bacteria, Viruses and Fungi.

Your skin has acidic oil that can catch or denature these foreign bodies.Your skin also serves to block these pathogens from diffusing into your blood stream.

Stomach Acid and Saliva serve to denature these pathogens.

Line 2: Innate and Fast:

Cells Responsible: Macrophages, Dendritic Cells, Mast Cells, Neutrophils, Natural Killer Cells, Basophils, Eosinophils, and More.

If the first line of defense fails and your blood happens to come in contact with pathogens these general cells recognize a wide range of general pathogens and forgo phagocytosis  with essentially means eating the foreign body or they inject the cells with a kind of ‘poison’ per say.

Line 3: Adaptive/Acquired Immunity (slow):


Dendritic cells have proteins that pick up everything they eat and present them on their surface.

So to not induce unwanted immune responses, every B and T cell in your body (that hasn’t resulted from a previous infection) is unique in what pathogen it can recognize (1 Cell to 1 specific epitope (antigen binding site)).

Helper T-Cells recognize the antigen presented on the surface of the Dendritic cells and start to divide, they then go and start trying to activate B cells and Cytotoxic T cells, but only those who and specifically bind to the epitope! It is worth noting that, for a B cell to be activated, it needs to both, be exposed to the pathogen itself, and be activated by the helper T Cell by direct contact. The cytotoxic T-Cell is activated by recognizing secrete chemical signals (cytokines) which provoke it to migrate to the pathogen, once it recognizes a pathogen it begins to divide.

Cytotoxic T cells do what their name implies, kill the cells, but because your body only has a few of the specific type of T cell that will recognize said antigen, it starts to divide. The new cells will either go to fight the infection or lay dormant in preparation for that same kind of infection.

B cells divide in the same way, but instead of directly killing the cells, the make and secrete antibodies that bind to the specific epitope for which that B cell is made to respond to.

Antibodies can do many things to a pathogen.

  • Neutralization- Renders pathogen ineffective
  • Agglutination- Clumps pathogens many together
  • Precipitation- Similar to agglutination, except is facilitates a phase change dissolution.

It is important to note that this does not happen quickly (hence why it takes time to fight off an infection), because it relies on the random nature of, often times, a single cell (B cell) being exposed to 2 different and independent things, along with the cytotoxic T-cell being exposed to the cytokines released by the helper T-Cells.