Specific Immunity: the body’s 3rd line of defense

The Immune System is the Third Line of Defense Against Infection

Specific Immunity Basics… Specific Immunity- the body’s way of attacking a specific type of pathogen Mechanisms involved do not attack everything that’s bad These mechanisms are considered your body’s 3rd line of defense Specific Immunity cells in your body use the “lock & key” method of identification- distinguish “self” from “not self (pathogen)”

TO BE IMMUNE TO A PATHOGEN, YOU MUST HAVE CONTACT W/ THE ANTIGEN FROM THE PATHOGEN AFTER CONTACT= IMMUNITY Must meet or be primed by specific pathogen before it can protect the body

Specific Immunity Naturally Acquired Active- Body generates an immune response to antigens. Immunity may be lifelong (chickenpox or mumps) or temporary (influenza or intestinal infections). B. Passive- Antibodies pass from mother to fetus via placenta or breast feeding (colostrum). No immune response to antigens, short lived

Specific Immunity Artificially Acquired A. Active Antigens are introduced in vaccines (immunization). Body generates an immune response to antigens. Immunity can be lifelong (oral polio vaccine) or temporary (tetanus toxoid) B. Passive Immunity: Preformed antibodies (antiserum) are introduced into body by injection. Snake antivenom injection from horses or rabbits. Immunity is short lived (half life three weeks). Host immune system does not respond to antigens.

Specific Immunity Basics… - Antigens and Ligands are like “flags” Almost all of your body cells have Ligands, protein markers attached to their plasma membrane these are “self” marker proteins Foreign pathogens have Antigens on their surface -these are “not self” marker proteins Auto Immune Diseases

Specific Immunity Basics Continued… Important cells involved include: Macrophages T-Lymphocytes (T-Cells) Helper T-cells Cytotoxic T-cells Memory T-cells B –Lymphocytes (B-Cells) -Plasma B-cells -Memory B-cells

Specific Immunity Basics… Resistance=Immunity Happens AFTER the first exposure to pathogen Memory cells will launch a faster, more massive, attack Quicker Response because-Memory cells “remember” pathogen from before and attack it immediately Reason for vaccinations

Antibody Response After Exposure to Antigen

Specific Immunity: B cells (3rd line of defense continued)

Antibodies are Produced by B Lymphocytes

How do B cells respond to foreign Invaders? AntiBody-Mediated Response- “humors”- fluid of blood or lymph B cells mature in red bone marrow extracellular, bind to bacteria, toxins, free viruses Before they enter cells useless against viruses, TB, other invaders that slip into cells B cells create plasma cells which release antiBodies, antibodies are receptors Mark cells for phagocytes to attack Your body make 100 million lymphocytes/day If the same # does not die, you can develop leukemia

Antibody Mediated Response cont. Apoptosis Programmed cell death (“Falling away”). Human body makes 100 million lymphocytes every day. If an equivalent number doesn’t die, will develop leukemia. B cells that do not encounter stimulating antigen will self-destruct and send signals to phagocytes to dispose of their remains. Many virus infected cells will undergo apoptosis, to help prevent spread of the infection.

Clonal Selection of B Cells is Caused by Antigenic Stimulation

How do B cells respond to foreign Invaders? Steps of B cell response Pathogen (foreign antigen) enters tissue. 2. macrophage engulfs foreign pathogen and displays antigen 3. Helper T cell joins with antigen through “lock and key” and releases cytokines

4. B cell becomes activated (turn on robot and program it to kill one thing/pathogen) because of chemical signals 5. B cell proliferates. (clone robots to kill a bunch of the same thing/pathogen) 6. B cells differentiate into plasma cells and memory cells. (split your army)

7. Plasma cells secrete antibodies to attack the pathogen and stop the reproduction (why we call it antibody mediated response) 8. Memory cells will circulate through the body ready for a 2nd attack (why is this advantageous?) https://askabiologist.asu.edu/b-cell

How do T cells respond to foreign invaders? Cell-mediated Immunity - Cell to cell contact, lymphocyte response Genes are receptors, NOT antibodies T- cells mature in Thymus More diverse and complex Virus infected, bacteria infected, cancer cells, and cells of foreign grafts are destroyed, inside of cells Destroy/lyse cells infected or cancerous

Cell Mediated Immunity is Carried Out by T Lymphocytes

How do T cells respond to foreign invaders? Steps for T cell response: Pathogen (foreign antigen) enters tissue 2. Macrophage phagocytizes pathogen 3.Macrophage displays foreign antigen on cell surface.

(reference your diagram) Steps… 4. Helper T cell joins with antigen through lock and key (puzzle pieces fit) 5. Helper T cell secretes cytokines (sprinkles)

(reference your diagram) Steps… T cell becomes activated- enzymes activate lymphocyte response T cells proliferate- make more of themselves T cells differentiate into cytotoxic T cells and memory T cells Some sytoxic T cells are not activated on 1st exposure, it might take another exposure

Steps… 9. Cytotoxic T cells bind with pathogen and release substances that destroy pathogen. cyto= toxic= 10. Memory cells will circulate through the body ready for a 2nd attack/exposure

Overview of the Immune Response