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?

You essentially have 3 lines of defense to prevent disease.

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





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: T Cells:

If the first line of defense fails and your blood happens to come in contact with pathogens these general cells this forgo phagocytosis  with essentially means eating the foreign body.

Line 3: B Cells:

If for some reason the T Cells cannot seem to beat this pathogen these specialized Leukocytes will produce antibodies to help them out. What are antibodies? Read on to learn more about the immune response.

Before we talk about the inflammatory response lets define a few terms.

Leukocyte: Also called phagocyte, antigen presenting cell, or generally white blood cell help defend your body from pathogens.

Immune Response: Also called inflammatory response.

Types of Leukocytes

Neutrophil- Attacks Bacteria and Fungi

Eosinophil-Attacks Large Parasites and Allergens

Basophil-Attacks Releases Histamine (Attracts other leukocytes)

Lymphocyte- B Cells and T Cells

B Cells- Release Antibodies

T Cells

CD4+Regulate B Cells and T Cells

CD8+ Attack Virus infected Cells


Monocyte-Specialized T cells by tissue i.e. Kupffer Cells in Liver

Relationship between Antibodies and Antigens

Antigens: Part of a Cell or Molecule capable of binding to an Antibody (the part it binds to is called the epitope)

Antibody: A molecule that binds to an Antigen

Antibodies will bind to Antigens on cells or molecules, if a cell or molecule has an antigen that binds with an antibody that you possess it is considered foreign by your leukocytes and will subsequently be attacked by your Phagocytes.

Antibodies can do many things to a pathogen besides marking it as a foreign body like

  • Neutralization- Renders pathogen ineffective
  • Agglutination- Clumps Pathogens many together
  • Precipitation- Similar to agglutination

Immune Response to Viruses

Now that we have defined some terms lets go into the specific immune response for viruses in order to understand vaccines.

You essentially have two types of immune responses that interact with each other.

Specific and Nonspecific


Adaptive and Innate

Nonspecific refers to Leukocytes and Phagocytes reacting to something because it has some sort of abnormality and essentially eating it.

Your adaptive immune response has to do specifically with your Lymphocytes and are what concerns vaccinations.

We already know that Lymphocytes can be divided into B Cells and T Cells, but how do they interact? And what are their roles?

Both cell types are made in the bone marrow, but T cells are differentiated in the thymus.

B Cells are associated with the Humoral Response.

T Cells are associated with the Cell Mediated Response.

The Humoral response refers to pathogens that are exterior to your cells, in the Humoral fluid of your body. Cell mediated is when the pathogen enters a cell and the cell itself must be destroyed.

First lets go over the Humoral Response:

Your B cells have membrane bound antibodies.

Each B Cell has thousands of the same membrane bound antibody and some B cells have different antibodies than others.

That means there are likely millions of different B Cells in your body at this given moment. Each that respond to a different foreign pathogen.

When you are exposed to a pathogen it may take a long time for it to run into the specific B Cell that can bind to it. This time allows the pathogen to reproduce and become threatening.

However once it binds to the right B cell that B Cell reproduces into effector B cells or plasma Cells and memory B Cells.

The effector B Cells begin producing antibodies and the memory B cells stay around in larger numbers in case that same virus comes back your body will be prepared to fight it.

But it is important to remember that the Humoral response is usually just a reaction to the nonspecific response.

What I mean by this is your nonspecific response is simply phagocytes going around and eating foreign bodies.

But once the do this, inside the phagocyte it will ligate or break apart this foreign body and present part of it on the outside of its cell membrane on something called the MHC II complex.

B Cells will usually bind to this in stead of the actual pathogen itself. This allows for B cell differentiation even if your Innate response is adequate.

It is important to note that this is mediated by CD4+ T Cells.

The too will bind to this MHC II complex.

And like B cells they differentiate into effector T Cells and Memory T Cells.

Again this prepares your body for another encounter with the same pathogen.

Essentially what these CD4+ T Cells do is release cytokines that tell other leukocytes to come to the location of that pathogen.

Leukocytes like phagocytes that will eat the pathogen, CD8+ T Cells that will poison the pathogen, and B Cells that will release antibodies to opsonize the pathogen.