Immune SystemImmune System

Review

What is an immune system? The system in the body responsible for maintaining

homeostasis by recognizing harmful from non harmful organisms and by producing an appropriate response

What is immunity? The ability of the body to fight infection and/or foreign

invaders by producing antibodies or killing infected cells Different types: Natural Active, Natural Passive, Artificial

Active, Artificial Passive

How does the body fight infection/foreign invaders?

The Body’s THREE lines of DefenseFirst Line of Defense – The Skin

• Provides Physical and Chemical barriers Physical – hard to penetrate, made of indigestible keratin Chemical – tears, sweat, saliva and mucous (chemicals and

enzymes in body fluids)

First Lines of DefenceFirst Lines of Defence

skin prevents entry

tears antibacterial enzymes

saliva antibacterial enzymes

stomach acid low pH kills harmful microbes

mucus linings traps dirt and microbes

“good” gut bacteria

White Blood Cells (Leukocytes)

1. Granulocytes (50-60%) (basophil, eosinophil, neutrophil) release powerful granules that have chemicals inside that

attack an intruder *Basophil produce histamine (high during allergic reactions)*Eosinophil (high in parasitic invasion) *Neutrophil (aid in phagocytosis, high during bacterial

infection)

2. Monocytes (7 %) When activated become macrophages that engulf antigens

3. Lymphocytes (30-40 %) T- Cells and B-Cells (Viral infections)***All WBC are produced in the bone marrow as stem cells – T-

cells migrate to the thymus – that’s where they mature ***WBC are found in lymph nodes, spleen & liver

Second Line of Defense – Nonspecific Immune Response

These are defenses the body uses no matter what the invader may be. These defenses include: Phagocytosis – done by Macrophages Inflammation - caused by release of

Histamine from leukocytes Fever – caused by histamines. The fever

(high temp) kills invaders by denaturing their proteins.

PhagocytosisPhagocytosis

Stages in phagocytosis1. Phagocyte detects chemicals released

by a foreign intruder (e.g. bacteria)2. Phagocyte moves up the concentration

gradient towards the intruder3. The phagocyte adheres to the foreign

cell and engulfs it in a vacuole by an infolding of the cell membrane.

4. Lysosomes (organelles which are rich in digestive enzymes & found in the phagocytes cytoplasm) fuse with the vacuole & release their contents into it.

PhagocytosisPhagocytosis

5. The bacterium is digested by the enzymes, and the breakdown products are absorbed by the phagocyte.

During infection, hundreds of phagocytes are needed.

Injury

Chemical signals are released by the foreign invader Chemicals cause capillaries to dilate thus increasing blood

flow Basophils flow through the blood stream and gather to the

site of infection and release histamine (histamine cause inflammation and increase blood flow)

This brings neutrophils and monocytes to the site Neutrophils release chemicals that engulf and kill antigens

* they have a short lifespan but are constantly supplied * dead neutrophils form pus macrophages engulf and kill antigens and dead neutrophils

***Inflammation response (swelling, heat, redness & pain) TREATMENT???

Fever

The hypothalamus responds to a chemical signal caused by the presence of a pathogen

The signal makes the hypothalamus increase the normal set point for normal temperature in the body from 37◦C t0 ~39◦C (Optimal)

WHY? Some hypothesize that immune cells function more

effectively at that temperature Invaders/pathogens are not so equipped with dealing

with heat (High temp. denatures their proteins)

***This is a specific response to a specific pathogen/antigen.

The response involves lymphocytes and the creation of Antibodies.

There are 2 types of lymphocytes :

***T-cells – identify and attack foreign substances, regulate B-cell production and stop the immune response

***B-cells – produce antibodies and are

programmed to respond to a specific antigen

Third Line of Defense – Specific Immune Response

AntigensAntigens

all cells have surface markers called antigens.

body can recognize these as self or non-self (foreign)

Specific responseSpecific response

Lymphocytes detect presence of foreign antigens

Stimulated to produce specific proteins called antibodies.

How an antibody operates/works?

Deactivation of a bacterium by an antibody.

The Pathway of Specific Immune Response

Pathogens

Pathogens eaten by Macrophage

Displays portion of Pathogen on surface

Helper-T cell recognizes Pathogen

Step 1

Step 2

Step 3

Activates B- CellActivates Cytotoxic

T- Cell

Memory B-CellMemory T-Cell

Kills Infected CellsAntibodies

Immune Response Explained

1. Antigen infects cells.2. Macrophage ingests antigen and displays portion on its

surface.3. Helper T- Cell recognizes antigen on the surface of the

macrophage and becomes active.4. Active Helper T-Cell activates Cytotoxic T-Cells and B-Cells.5. Cytotoxic T-Cells divide into Active Cytotoxic T-cells and

Memory T – Cells.6. Active Cytotoxic T-Cells kill infected cells.7. At the same time, B-Cells divide into Plasma Cells and

Memory B- Cells.8. Plasma cells produce antibodies that deactivate pathogen.9. Memory T and Memory B cells remain in the body to speed

up the response if the same antigen reappears.10. Supressor T-Cells stop the immune response when all

antigens have been destroyed.

Cellular Immunity .vs. Antibody Immunity

Carried out by T-Cells Infected cells are killed by

Cytotoxic T –Cells.

Carried out by B-cells Antibodies are produced

and dumped into blood stream.

Antibodies bind to antigens and deactivate them.

Cellular Immunity Antibody or Humoral Immunity

Immune Response Summary

Antigen

Macrophage

Helper T - Cell

Active Cytotoxic T-Cell Active B - Cell

Kills Infected Cells Memory T- Cell Plasma Cell Memory B-Cell

Antibodies

Deactivates Antigens

Displays copy of antigen on surface of cell

Cellular ImmunityAntibody Immunity

What happens during an allergic reaction?Anaphylaxis or anaphylactic shock:

This is the sudden and severe allergic reaction to a substance that can cause death.

During an allergic reaction, antibodies cause histamines to be released from certain cells. In addition blood vessels dilate which causes a decrease in blood pressure and heart rate.

Histamines cause:a. Swelling of tissuesb. Release of fluids (runny noses and eyes)c. muscle spasms (some cases)

Treatments for Allergies1. Avoidance of material – especially food.2. Epinephrine – “epi – pen”3. Antihistamines -- benadryl