The Human Immune System

What is the Immune System?

The Immune System is a complex system that is responsible for protecting us against infections and foreign substances.

Immune System : 2 branches

The Innate Immune System = Present at the time of birth or that develops during

maturation.

The Adaptive Immune System = Which is acquired as a result of prior experience with

a foreign substance.

Cells of Immune System

Steam Cell: An undifferentiated cell of a multicellular organism which is capable of giving rise to indefinitely more cells of the same type and from which certain other kinds of cell arise by differentiation.

Lymphoid Steam Cell: Lymphoid stem cells give rise to the lymphocytes, which specifically identify foreign molecules and cells.

Myeloid Progenitor: Myeloid cells include monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, dendritic cells and megakaryocytes or platelets. Lymphoid cells include T cells, B cells, and natural killer cells.

Neutrophil: Neutrophil (also known as neutrophils or occasionally neutrocytes) are the most abundant type of granulocytes and the most abundant (40% to 75%) type of white blood cells in most mammals. They form an essential part of the innate immune system.

Eosinophil: A white blood cell containing granules that are readily stained by eosin.

Basophil: A basophilic white blood cell.  Basophils contain anticoagulant heparin, which prevents blood from clotting too quickly. They also contain the vasodilator histamine, which promotes blood flow to tissues.

Mast Cell: A cell filled with basophil granules, found in numbers in connective tissue and releasing histamine and other substances during inflammatory and allergic reactions.

Memory Cell: A long-lived lymphocyte capable of responding to a particular antigen on its reintroduction, long after the exposure that prompted its production.

Plasma Cell: Plasma cells, also called plasma B cells, plasmocytes, plasmacytes, or effector B cells, are white blood cells that secrete large volumes of antibodies. 

Viruses

Viruses and bacteria are everywhere. Some of them want to invade our body.

Viruses enter body cells, hijack their organelles, and turn the cell into a virus making-factory. The cell will eventually burst, releasing thousands of viruses to infect new cells.

Cell before infection… …and after.

How does our body defend itself against Viruses and Bacteria?

Defense Against Disease

If these barriers are penetrated,the body responds with

If the innate immune response is insufficient,the body responds with

Adaptive Immune ResponseCell-mediated immunity, Humoral immunity

Nonspecific External BarriersSkin, Mucous membranes

Innate Immune ResponsePhagocytic and natural killer cells,

Inflammation, Fever

3 lines of defense

1.First 2. Second 3. Third

Line Line Line

First line of defense

Skin

- The dead, outer layer of skin, known as the Epidermis, forms a shield against invaders and secretes chemicals that kill potential invaders .

- We shed between (40 – 50) thousand

skin cells every day.

- As we breathe in, foreign particles and bacteria bump into Mucus throughout our respiratory system and become stuck.

- Hair-like structures called Cilia sweep this mucus into the throat for coughing or swallowing.

Mucus and Cilia

- Swallowed bacteria are broken down by incredibly strong acids ( HCl , NaCl , KCl ) in the stomach that break down our food.

- The stomach must produce a coating of special mucus or this acid would eat through the stomach.

Stomach Acid

White Blood Cells

- If invaders actually get within the body, then our white blood cells (WBCs) begin their attack.

- WBCs normally circulate throughout the blood, but will enter the body’s tissues if invaders are detected.

These white blood cells are responsible for eating foreign particles by engulfing them.

Once engulfed, the phagocyte (a type of cell within the body capable of engulfing and absorbing bacteria and other small cells and particles) breaks the foreign particles.

T-Cells

T-Cells, often called “Natural killer” cells, recognize infected human cells and cancer cells.

T-cells will attack these infected cells, quickly kill them and then continue to search for more cells to kill.

Antibodies- Antibodies are large Y-shaped

protein molecules created by the immune system to identify and neutralize foreign objects and pathogens, such as bacteria, viruses, fungi, parasites, and toxins. Also known as immunoglobulin.

- Antibody defends the body against a specific type of antigen ( foreign particles).

- It is estimated that humans are capable of generating about 10-billion different kinds of antibodies.

Antibody Production

- WBCs gobble up invading particles and break them up.

- Antibodies are manufactured by white blood cells called B-lymphocytes, or B-cells.

Antibodies function:

They bind directly to antigens, effectively coating the surface of the invader, in order to prevent pathogens from entering or damaging healthy body cells. Antibodies can also stimulate other parts of the immune system (e.g. complement proteins) to destroy the pathogens. And antibodies can mark pathogens through a process called ’Opsonization’ so that the pathogens can be identified and neutralized by other immune cells.

Role of the antibodies:

What is immunity?

- Resistance to a disease causing organism or harmful substance.

- Two types- Active Immunity- Passive Immunity

Types of Immunity

Active Immunity

- WE produce the antibodies- Our body has been exposed to the antigen in the past

either through:- Exposure to the actual disease causing antigen – we

fought it, we won, we remember it.- Planned exposure to a form of the antigen that has been

killed or weakened – we detected it, eliminated it and remember it.

VaccineAntigens are deliberately introduced into

the immune system to produce immunity.Because the bacteria has been killed or

weakened, minimal symptoms occur.Have eradicated or severely limited

several diseases from the face of the Earth, such as polio and smallpox.

How long does active immunity last?

It depends on the antigen.

Some disease-causing bacteria multiply into new forms that our body doesn’t recognize, requiring annual vaccinations, like the flu shot.

Booster shot - reminds the immune system of the antigen.

Others last for a lifetime, such as chicken pox.

Passive Immunity

We don’t produce the antibodies. A mother will pass

immunities on to her baby during pregnancy through placenta.

These antibodies will protect the baby for a short period of time following birth while its immune system develops.

Immune DisordersAllergies

- Immune system mistakenly recognizes harmless foreign particles as serious threats.

- Launches immune response, which causes sneezing, runny nose, and watery eyes.

- Anti-histamines block effect of histamines and bring relief to allergy sufferers.

Acquired Immune Deficiency Syndrome (AIDS)

Caused by the Human Immunodeficiency Virus.

Discovered in 1983.Specifically targets and

kills T-cells.Because normal body

cells are unaffected, immune response is not launched.

AIDS

- The HIV virus doesn’t kill us – it cripples our immune system.

- With our immune system shut down, common diseases that our immune system normally could defeat become life-threatening.

- Can show no effects for several months all the way up to 10 years.

Autoimmune Diseases

Our body's immune system protects us from disease and infection. But if we have an autoimmune disease, our immune system attacks healthy cells in our body by mistake. Depending on the type, an autoimmune disease can affect one or many different types of body tissue. It can also cause abnormal organ growth and changes in organ function.

There are as many as 80 types of autoimmune diseases. 

Causes of Autoimmune Diseases:

The cause of autoimmune disease is unknown. There are many theories about what triggers autoimmune diseases, including:

bacteria or virusdrugschemical irritantsenvironmental irritants

Common Autoimmune Diseases:

Rheumatoid Arthritis: inflammation of joints and surrounding tissues.

Systemic Lupus Erythematosus: affects skin, joints, kidneys, brain, and other organs.

Type 1 Diabetes: destruction of insulin producing cells in the pancreas.

Reactive Arthritis: inflammation of joints, urethra, and eyes, may cause sores on the skin and mucus membranes.

How are Autoimmune Diseases treated?

eat a balanced and healthy dietexercise regularlyget plenty of resttake vitamin supplementsdecrease stressMedical interventions include:hormone replacement therapy, if necessaryblood transfusions, if blood is affectedanti-inflammatory medication, if joints are affectedphysical therapy