*Authors note: this presentation was not made for school purposes

By Tai Kao-Sowa

Immunology

The Immune system The immune system is the integrated body system of organs,

tissues, cells, and cell products such as antibodies that differentiates self from non-self and neutralizes pathogenic organisms and substances.

This definition involves both the innate immune system and the adaptive immune system. Both of these will be covered more later.

Specific immunity (aka acquired/adaptive immunity) employs components of the immune response that specifically recognize and selectively eliminate microorganisms and molecules perceived as foreign by the host.

Nonspecific immunity (aka innate immunity) utilizes the basic resistance to disease that a species possesses and makes up the first line of defense.

Innate Immune System The innate immune system is the first defense of the body

against invasive pathogens. They respond in a generic, non specific way, unlike the adaptive immune system.

The innate immune system is the dominant immune system found in plants, fungi, insects, and primitive multicellular organisms.

Mast cells and Leukocytes (most of which are phagocytes) make up the innate immune system.

The main phagocytes are Macrophages.

Mast cells Mast cells are in many different tissues and contain many

granules rich in histamine and heparin.

Mast cells are best known for their role in allergies and anaphylaxis, but they play an important part in communicating with the immune system in the early stages of infection.

Mast cells decide on the potency of the infection and whether or not to activate immune cells to destroy the pathogen or inhibit them to prevent an excessive immune system reaction.

Macrophages and the Innate Immune System

Macrophage: A type of white blood that ingests foreign material. Macrophages are key players in the immune response to foreign invaders such as infectious microorganisms.

Blood monocytes migrate into the tissues of the body and there evolve into macrophages.

Macrophages help destroy bacteria, protozoa, and tumor cells using phagocytosis. They also release substances that stimulate other cells of the immune system.

Neutrophils Neutrophils are a type of aggressive white blood cell. They

are the most numerous white blood cells in animals (they account for 70% of all leukocytes/white blood cells) and are essential to the bodies innate immune system.

Neutrophils are one of the first cells to come to a site of inflammation, and they are the hallmark of acute swelling.

Neutrophils are phagocytes, which means they can ingest microbes or particles. They extend two pseudopods around their target and then connect them at the end (a type of endocytosis). Once inside the neutrophil, the microbe is killed by the means of an oxidative burst, which is the neutrophils way of making sure the microbe doesn’t replicate inside it and burst the cell.

Neutrophil Transportation

Neutrophils follow pathogens by sensing chemicals. This process is called chemotaxis. However, until it reaches the area the pathogen is in it has to rely on signals from mast cells. There are 4 main steps to get to the pathogen.

1. Rolling adhesion (the neutrophil sticks and rolls to the side of the blood vessel it is in).

2. Tight binding (the neutrophil sticks more and stops rolling).

3. Diapedesis (the neutrophil squeezes through the cells lining the artery).

4. Migration (the neutrophil moves to the site of inflammation).

Large white blood cells that attack cells that have been infected by pathogens, not the pathogen themselves. They are particularly effective in killing cancer cells and cells infected with viruses.

A Natural Killer Cell punctures the cell membrane of its target cell, allowing water to rush into the cell, causing the cell to burst.

Natural Killer Cells

Note: Natural Killer Cells do not need to recognize antigens to kill infected cells.

Acquired Immune System Vaccination – term used to explain how healthy subjects are inoculated

with weakened strains of pathogens to induce acquired protection.

The acquired immune system is the identification of pathogens and the elimination of them by small lymphocytes. (A type of white blood cell). Small lymphocytes have memory (They can recognize pathogens).

Koch’s postulates show that disease is caused by one of the four major groups of pathogens:

Viruses Bacteria Pathogenic fungi Parasites

Small lymphocytes are broken into two categories:

T-cells

B-cells

The Immune Response involves several organs, as well as White Blood Cells in the Blood and Lymph. These include the BONE MARROW, THYMUS, LYMPH NODES, TONSILS, ADENOIDS, AND SPLEEN.

Each organ of the immune system plays a different role in defending the body against pathogens.

Bone Marrow manufactures the billions of WBC needed by the body every day.  Some newly produced WBC remain in the bone marrow to Mature and Specialize, while others travel to the Thymus to Mature.

Lymph Nodes Filter Pathogens from the Lymph and expose them to White Blood Cells

The Spleen, a fist-sized organ located behind the stomach, Filters Pathogens from the Blood.  It is stocked with WBC that respond to the trapped pathogens.

Where is it?

Lymphatic vessels

Lymph nodes

Thymus

Spleen

Tonsils andadenoids

Bone marrow

Appendix

Peyer’s patches

Primary lymphoidorgans

Secondary lymphoidorgans

T-cells (Thymus cells)

There are two main types of T-cells: Helper T-cells and Cytotoxic T-cells.

Antigen: A toxin or other foreign substance that induces the production of antibodies. (Antibody generating)

Antibodies: A blood protein produced in response to and counteracting a specific antigen.

Thymus cells originate in the thymus, hence the name thymus cell. T-cells have a special receptor on their outer membrane called T cell receptors. These distinguish T-cells from other lymphocytes.

Helper T-cells Helper T-Cells assist other white blood cells in

immunological processes, including the maturation of B-cells into plasma cells and the activation of cytotoxic T cells and macrophages. They also coordinate immune responses in your body.

Cytotoxic T-cells

Cytotoxic T-cells destroy infected cells, tumor cells, and other damaged/dysfunctional cells by inducing apoptosis (programmed cell death).

These cells are essential because they can also eliminate virus infected cells, helping to prevent the spreading of the virus.

Cytotoxic T-cells and Natural Killer Cells have a similar function. The main difference is that NK cells are non-specific and cytotoxic T-cells are specific- that is they recognize viral antigens ona cell before killing it.

Stimulating a B-cell When a macrophage or B-cell finds a pathogen, it ingests it

using phagocytosis, a type on endocytosis. It then semi-digests the cell, and then class 2 MHC proteins bind with the antigen fragments and bring it up to the surface of the macrophage to display. The macrophage is now called an antigen presenting cell.

Once a Helper T-cell connects with this antigen presenting cell, a series of chemicals stimulate T-cells to clone/reproduce.

If a B-cell becomes an antigen presenting cell, and if the antigen is the same antigen as the one that the macrophage presented to the T-cell, then when the B-cell connects with the T-cell, the T-cell stimulates B cells by inserting cytokines into the B cell, stimulating clonal selection (replication). These “clones” are plasma cells, which produce antibodies and release them into the blood stream. The antibodies then destroy or inhibit any pathogen that has the same antigen as the one that was recognized by the B-cell.

B-cells

The principle function of B-cells is to make antibodies against antigens.

Once a B-cell is activated by a T-cell, it transforms into a plasma cell. A number of changes accompany this, including cytoplasm and endoplasmic reticulum expansion, an active increase of transcription in organelles, and the secretion of antibodies.

Once a B-cell has produced an antibody for an antigen, it will remember that antigen in the future and produce antibodies quicker.

This is why B-cells are part of the learned immune system.

B-cells are produced in the bone marrow of most animals.

oops…

In some cases, a virus can have an antigen that is similar to the bodies antigen.

When this happens, your body produces antibodies that attack itself.

Until recently, this proved to be fatal. Luckily, with new technology there is only a 13% death rate.

The treatment involves plasma centrifuge and most likely dialysis, depending on the antigen targeted.