Immune 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 Defense First 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 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.

Phagocytosis Stages in phagocytosis 1. Phagocyte detects chemicals released by a foreign intruder (e.g. bacteria) 2. Phagocyte moves up the concentration gradient towards the intruder 3. 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.

Phagocytosis 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

Antigens Antigens all cells have surface markers called antigens. body can recognize these as self or non- self (foreign)

Specific 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- Cell Activates Cytotoxic T- Cell Memory B-Cell Memory T-Cell Kills Infected Cells Antibodies 

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-CellActive B - Cell Kills Infected CellsMemory T- CellPlasma CellMemory B-Cell Antibodies Deactivates Antigens Displays copy of antigen on surface of cell Cellular Immunity Antibody 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 tissues b. Release of fluids (runny noses and eyes) c. muscle spasms (some cases) Treatments for Allergies 1. Avoidance of material – especially food. 2. Epinephrine – “epi – pen” 3. Antihistamines -- benadryl