Honors Biology - Immune System Test

microbe

any microscopic living organism (something you need a microscope to see)

• indicates → size and living status

• does not indicate → helpful or harmful

• ex. Bacteria, viruses, fungi (like yeasts and molds).

pathogen

any biological agent that causes disease

• indicates → harmful

• not indicated → size or living status

• Examples

  • bacteria

  • fungi (some microscopic, some not)

  • protists,

  • viruses → not living (no cells) → not microbes

  • prions → infectious proteins (not living → not microbes); misfolded proteins that cause brain disease

  • multicellular parasites (tapeworms, etc.)

allergens

substance that causes an allergic (immune) response

• Specific molecules, such as food proteins and pollen grains, which noninfectious, but the immune system mistakenly recognizes them as threats and reacts like they are dangerous invaders.

innate immune response

• The body’s first line of defense against an invader

• non-specific → the response is independent of the type of invader (same for all)

• born with innate response

adaptive (aquired) immune response

• A specific immune response that develops over time after exposure to a pathogen

• Occurs when the innate response is insufficient

• slower, but more efficient

• It involves the activation of lymphocytes (T cells and B cells) that target specific antigens. mature by developing receptors on cell surface on last page of lesson 2

• Arises b/c exposure to antigen

  • natural exposure (active immunity) → sick, infected by pathogen

  • artificial exsposure (active immunity) → vaccines

• can also get passive immunity from breast milk or antivenom

innate external barriers (physical, chemical, biological)

• prevents pathogens from entering the body

  • Ex. mechanical barriers, chemical barriers, biological barriers

Mechanical barriers

• external barriers like skin and hair

• mucous membranes → line internal surfaces that are open to the enviroment (urinary, digestive, etc.)

  • mucus provides protection for cells below the mucus → prevents progress of foreign invader

  • in respatory system → cilia allow for mucus w/ particles/invaders to be brought to pharynx

Chemical barriers

chemicals near openings and on inner linings that protect non-specifically

• mucus-producing cells also make antibacterial enzymes

• in digestive system: gastic juice (low pH → acidic)

• in urinary system: uring (acidic)

  • in reproductive system: vaginal secretion (acidic)

biological barriers

living organisms that destroy invaders non specifically

• good bacteria in digestive tract + reproductive system → keep invaders from proliferating b/c have to complete with good bacteria

innate internal defense

• if first part of the innate defense (external) is breached and foreign invader enters the body, the internal defenses are used to prevent further infection

• Ex. innate immune cells, defensive proteins, inflammatory response, and fever response

innate immune cells (types of white blood cells)

• part of innate internal defenses and work non specifically (before the adaptive response)

• Phagocytes

  • nuetrophils (circulate in blood)

  • macrophages (circulate in interstitial fluid)

  • target foreign invaders with phagocytosis (engulf substances from enviroment → with food vacuoles and lysosomes)

• Natural Killer Cells (NKCs)

  • kill infected body cells (virus, cancerous) non-specifically

  • scan the body for cells that are missing their “ID tags”

  • not invaders but infected/damaged cells “self cells”

defensive proteins

function non-specifically - before the adaptive response gets activated

• interferons (proteins)

  • infected cell detecrs infection → makes interferon (secretory protein) → go to another cell → causes production of antiviral proteins

• complement system of proteins → help mark pathogens for destruction and enhance inflammatory response.

inflammatory response

• Purpose: to disinfect and clean injured tissues

• Step 1 → Tissue injury; signaling molecules are released from mast cells and macrophages that cause nearby capillaries to dilate (goal to get more blood)

  • The presence of bacteria causes the activation of two types of white blood cells

  • macrophages produce signaling molecules → bring fluid to the infecred area (more blood flow to the area)

  • mast cells → release histamines that cause blood capillary dialation (widens) → larger diameter needed for more blood + capillaries become leaky

• Step 2 → Materials are released from the blood through the widened and leaky vessels

  • Materials (below) are released from the blood through the widenend and leaky vessels

  • plasma → fluid in blood

  • clotting proteins → aid in clotting

  • platelets → makes clot; cell fragments

  • activated complement proteins attract phagocytes from blood (nuetrophils)

  • Results in swelling, warmth, and redness

• Step 3 → Bacteria are englufed by nuetrophils

  • pus → dead cell debris

  • Nuetrophils eventually die or are destroyed

fever

• raise the set point (ideal temp)

• a response to a systematic (widespread, whole body) infection

antigen

• any molecule or particke that elicits an immune response

• ex. proteins on the capsule of bacteria and viruses as well as venom

• adaptive immunity remember the antigen

• They can be bound to a pathogen or be free floating.

lymphatic system (two functions)

• network of tubes, tissues, and organs that help maintain fluid balce in the body and supports immune function.

• Circulatory Function → to return fluid back to the circulatory fluid

  • 20 L (plasma) leaked into interstitial fluid → 17L reabsorbed → 3L become lymph (absorbed into lymphatic capillaries)

  • plasma (when in capillaries) → interstitial fluid (interstial spaces) → lymph (lymphatic vessels)

• Immune Funtion → to filter interstitial fluid to remove/destroy invaders

  • lymphatic capillaries are intertwined with blood capillaries to collect fluid that exits the blood

  • eventually returned to the blodstream (lymph nodes = filtering)

• Sturucture

  • Tubes

lymphatic system structure (tubes and tissues)

• Tubes → transport of lymph/fluids through lymphatic capillaries and vessels

• Tissues → concentrations/groupings of immune cells that are not organized into a defined organ but work together to protect a region of the body

  • ex. Peyers patches (cluster of lymphocytes found in mucous layer of small intestine)

  • ex. tonsils = clusters of lymphocytes found in the oral cavity

lymphatic system structure (organs)

• primary lymphoid organs → where lympocytes develop and mature

  • red bone marrow → where blood cells are produced, lymphocytes (including NKCs) are made, and where B-cells (B for bone marrow) mature

  • thymus → location where T cells (T for thymus) mature 

• secondary lymphoid organs → where lymphocytes mount their immune response; contain B and T cells and macrophages to detect and attack invaders

  • lymph nodes → lymph nodes filter the lymph that flow through it. Contain masses of lymphocytes and macrophages

  • spleen → filters the blood that flows through it

  • mucosa-associated lymphoid tissue (MALT) → collection of lymphatic system tissues located in the mucous membranes that line body passages open to the outside enviro.

    • Ex. tonsils, appendix, and Peyer’s Patches

B-cells (humoral immune response) overview

• antibody proteins used to attack foreign invaders in body fluid, removing them from it

• located in secondary lymphatic tissues

• millions of different B-cell b/c of different antigen receptors (born with)

T-cells (cell-mediated immune response) overview

• cells (cytotoxic T-cells) used to attack foreign invaders located in body cells; kill body cells infected with pathogens

• located in secondary lymphatic tissues

• 2 types cytotoxic T-cell and helper T-cells

antigen receptor vs. antibody

• An antigen receptor is the same as an antibody except that the antigen receptor is bound in the membrane of a B or T cell while an antibody is free floating.

• Antibodies and Antigen receptors have Antigen-binding sites that match specific epitopes.

Epitope

• Regions of an antigen with a specific shape.

• Associated with antibodies’ antigen receptor

B cell clonal selection (diagram)

	Many B-cells with different antigen receptors are waiting in a secondary lymphoid organ/tissue.
⬇
	Antigen binds to a B-cell that has corresponding antigen receptors.
⬇
	Once the B-cell receives signaling molecules for a helper T-cell the B-cell becomes activated (it makes identical cells specialized against the antigen that triggered the response)
↙                                    ↘
Some B-Cells differentiate into memory cells, which remain in the lymph nodes.			Some B-Cells differentiate into effector cells/plasma cells that secrete antibodies into the blood and lymph.
⬇			⬇
Wait to help activate the immune system upon subsequent infection.			Effector cells have extra RER so they can make more antibodies (secretory proteins) which bind with the antigen.
			⬇
			Antigens bound by antibodies are marked for destruction (Phagocytosis) by macrophages.

Cell Differentiation

Memory Cells vs. Effector Cells

• Memory Cells: 

  • Help activate the immune system upon subsequent infections

  • Last for decades

• Effector Cells:

  • Are highly effective at combating an existing infection.

  • Last for only 4 or 5 days before dying off

Antibodies

• Structure:

  • Y-shaped proteins made of multiple polypeptides

  • protein is stablized by disulfide bridges (covalent bonds)

  • Heavy chain → Interior polypeptide chains

  • Light chain → Exterior polypeptide chains

  • Disulfide Bridges

    • Stabilized by disulfide bridges

    • Covalent bonds -> Stronger than IMF’s

    • Cannot be denatured -> can go to many parts of the body with different environments

  • Variable Region → Is specific for antigen binding (bind to epitopes)

  • Constant Region → Shared by all antibodies

• Function:

  • Antibody binds to an antigen and inactivates the antigen by:

    • Neutralization (blocks viral binding sites; coats bacteria)

    • Agglutination (clumps viruses and cells together)

    • Precipitation (clumps of soluble antigens come out of solution)

    • Activation of complement proteins (free floating complement proteins are activated and form membrane complexes)

  • Neutralization, Agglutination, and Precipitation enhance…

    • Phagocytosis (foreign particles and cells are engulfed and digested)

  • Activation of complement proteins → Cell lysis (rupture of invading cell) aka. cell dies

T cells (types)

• Helper T-cells

  • Activate the humoral response by activating B-cells.

  • Activate cytotoxic T-cells

• Cytotoxic T-cells

  • Kill infected body cells

Anitgen Presenting Cells (APCs)

• can be macrophages or b-cells

• located in Interstitial Space and secondary lymphoid organs/tissues.

• Where are the Helper T-cells located in secondary lymphoid organs/tissues when contacted by apc

• What happens that causes cells to present antigens to the helper T-cell?

  • An APC ingests a microbe through a vacuole.

  • The storage vacuole combines with a lysosome.

  • The microbe is broken down into its antigens (nonself molecule)

  • The nonself molecule is combined with a self protein (which the APC makes) to form a Self-nonself complex.

  • The Helper T-cell with that specific antigen receptor identifies the antigen and binds to it.

The APC finally sends signaling molecules to activate the Helper T-cell.

so helper T needs signaling proteins and antigen thru self non self complex

Activated Helper T-cell

The activated Helper T-cell releases signaling molecules that do three things:

• Stimulate helper T-cell division (memory helper T-cells and effector helper T-cells)

• Activate B-cells (begins Humoral immune response)

Activates cell-mediated immune response (clonal selection: memory cytotoxic T-cells and effector cytotoxic T-cells)

Cytotoxic T-cells

• Kill infected cells

  • Bind to an infected cell

  • Perforin molecules make holes in membrane

    • Enzymes that promote apoptosis (programmed cell death) enter

  • Infected cell is lysed (destroyed)