Booklet 5: Immunity and Host Defense Flashcards
Define: Immunity
The body’s ability to resist disease
What are the two branches of immunity?
Innate - non-specific
Adaptive - acquired and specific
Describe innate immunity
- Protects humans from most infectious diseases
- Exists at birth and always present
- Natural host resistance
- NO MEMORY
- Can be specific for tissue
- Chemical and physical barriers, special immune system cells, physiological processes and molecular defences
T or F: susceptibility to pathogens varies from species to species
True
Example: Anthrax: Fatal blood infection in cattle vs cutaneous in humans
Why do pathogens prefer a specific body site to initiate infection?
Nutritional and metabolic needs.
Example: Clostridium tetani: ingested vs. deep wounds
How does the skin act as a chemical and physical barrier for infection?
- Prevents invasion by microbes
- Protective protein - keratin
- Slightly acidic - pH = 5
- High NaCl concentration (periodic drying)
Describe mucous membranes
-Mucous traps microbes
-Contains antimicrobial secretions
Examples:
- Lysozyme - cuts B-1,4, glycosidic bonds in peptidoglycan
- Defensins - antimicrobial peptides that poke holes in bacterial cell membranes
How does the gastrointestinal tract act as a chemical and physical barrier for infection?
Stomach: -Strong acidity (pH = 2) -Proteolytic enzymes -Destroys most microbes Small intestine: -Rapid change in pH -Pancreatic enzymes -Bile All of those help to destroy microbes
How does the respiratory tract act as a chemical and physical barrier for infection?
Known as the mucocilliary escalator:
- Ciliated cells line the mucous membranes of the airways
- Sweeping acton moves mucous and microbes away from the lungs
How does the large intestine act as a chemical and physical barrier for infection?
Has normal microbiota:
- Microbes that already reside in and on the human body
- Take up attachment sites
- Limit available nutrients
- Make antimicrobial compounds
How does the genitourinary tract act as a chemical and physical barrier for infection?
-Urine - metabolic waste products, toxic to many microbes
-Flushing action - mechanical removal of microbes
-Normal microbiota
Ex.-Vaginal epithelial cells produce glycogen. Then Lactobacillus acidophilus ferments the glucose to lactic acid which has a pH of about 3 or 5
What is the lymphatic system?
A collection of tissues that bring specialized cells (lymphocytes) into contact with foreign material (antigens)
What is the lymphatic system made up of?
- Lymph vessels that carry fluid (lymph)
- Lymphoid organs.
-Lymph is similar to blood containing white blood cells (leukocytes) but without red blood cells
What are primary lymphoid organs and what happens in them?
- Bone marrow
- Thymus
Leukocytes are produced and mature.
What are secondary lymphoid organs and what happens in them?
- Lymph nodes
- Spleen
- MALT
Contains leukocytes arranged to filter out microbes and antigens.
What is MALT?
Mucosa associated lymphoid tissue.
Leukocytes constantly sample their surroundings by phagocytosis looking for foreign material.
What are leukocytes and what are they involved in?
- They are white blood cells.
- They are cells that circulate in the blood and lymph, and reside in lymphoid organs
- Involved in both branches of immune response (innate and immunity).
What are they types of leukocytes?
- Granulocytes:
- Basophils and mast cells
- Eosinophils
- Neutrophils - Monocytes:
- Macrophages
- Dendritic cells - Lymphocytes
- B cells
- T cells
- NK cells
What are granulocytes?
- Cytoplasm contains granules filled with reactive chemicals
- Can kill microbes
- Signal other components of immunity
Granulocytes differentiate into:
- Basophils and mast cells
- Eosinophils
- Neutrophils
Describe basophils and mast cells.
- Non-phagocytic
- Circulate the blood (basophils) or reside in mucosal tissue (mast cells)
- Can be triggered to degranulate
- Release vasoactive mediators:
- Trigger inflammation
- Ex. histamine - involved in the allergic response
Granulocytes differentiate into:
- Basophils and mast cells
- Eosinophils
- Neutrophils
Describe eosinophils.
- They are granules stained with acidic dyes
- Non-phagocytic
- Can leave the blood and enter tissues of inflammation
- They attack large parasites such as protozoa and parasitic worms
- Release reactive oxygen intermediates that destroy parasite from the outside:
- O2, H2O2, and OH
Granulocytes differentiate into:
- Basophils and mast cells
- Eosinophils
- Neutrophils
Describe neutrophils.
- Granules filled with digestive enzymes such as lysozyme or defensins
- Circulate the blood and migrate to infection sites
- Highly phagocytic (they “eat” invading bacteria)
- Central component of innate immunity!
What are monocytes?
- They circulate the blood and then migrate into tissues.
- Differentiate into macrophages and dendritic cells.
- Strongly phagocytic cells involved in antigen presentation.
Monocytes differentiate into:
- Macrophages
- Dendritic cells
Describe macrophages.
- Reside in tissues such as lungs, liver, spleen, connective tissues.
- Specific surface molecules recognize pathogens - Toll Like Receptors
What are examples of Toll Like Receptors?
- LPS
- Peptidoglycan
- Fungal Cell Walls
They induce phagocytosis.
Monocytes differentiate into:
- Macrophages
- Dendritic cells
Describe dendritic cells.
- Reside in tissues that serve as common entry points for pathogens such as:
- skin
- mucous membranes of the nose, lungs and intestines
- They constantly sample surroundings by phagocytosis
- Migrate to lymphoid organs
- They then present foreign antigens on their surface to B and T lymphocytes which trigger the specific (adaptive) immune response.
What are lymphocytes?
- Specialized leukocytes involved primarily in the adaptive immune response.
- Circulate through the blood and reside in the lymphoid organs.
What are the 3 types of lymphocytes?
- B lymphocytes
- T lymphocytes
- Natural killer cells
Lymphocytes differentiate into:
- B cells
- T cells
- NK cells
Describe B cells.
- Antibody producing cells
- Involved in the humeral immune response
Lymphocytes differentiate into:
- B cells
- T cells
- NK cells
Describe T cells.
-Involved in the cell mediated immune response
Lymphocytes differentiate into:
- B cells
- T cells
- NK cells
Describe NK cells.
- Destroy abnormal body cells such as:
- Cancer cells
- Cells infected by a bacteria or a virus
Describe: innate immunity
- The innate ability to destroy a pathogen that has never been encountered before.
- Involves phagocytic leukocytes (neutrophils and macrophages) that recognize pathogen-associated molecular patterns
- lipopolysaccharide
- lipoteichoi acid
- flagellin
What is the major downfall of innate immunity?
NO MEMORY
What do phagocytes have?
Toll-Like Receptors which interact with a PAMP and trigger phagocytosis
Explain phagocytosis.
- Phagocytes engulf and destroy invading microbes
- Cell membrane invaginate around a foreign particle
- Engulfs it into a phagosome
- Phagosome fuses with a lysosome to form a phagolysosome
What is a phagolysosome filled with?
- Lysozyme and defensins
- Proteases (degrade proteins)
- Lipases (degrade phospholipids)
- Nucleases (degrade nucleic acids)
T or F: phagocytosis is a form of oxygen independent killing
True
Describe oxygen dependent killing
- Activated phagocytes produce reactive oxygen compounds
- Kill ingested microbes by oxidizing cell components
What happens once invaders have been killed?
Neutrophils perform exocytosis and fragments are expelled from the cell.
Macrophages and Dendritic cells become antigen presenting cells and fragments of the intruder are presented on the cell surface to trigger an adaptive immune response.
What is inflammation?
General non-specific reaction to pathogens, toxins, or tissue damage.
What are the 5 cardinal signs of inflammation?
- Redness
- Warmth
- Pain
- Swelling
- Loss of function
In response to an infection, what do injured tissue and leukocytes release?
Pro inflammatory cytokines
-blood vessels dilate and more leukocytes to the area
During inflammation, vessel walls become more _______ ?
Permeable.
Which allows leukocytes to squeeze into tissues (extravasation) and attack invading pathogens.
How does the temperature increase involved in inflammation affect the body?
Temperature increase may slow the growth of pathogens
What is the purpose of a blood clot?
Prevents movement of pathogens.
Describe the adaptive immune response.
- Acquired and Specific
- Acts against a specific intruder
- Acquired when a pathogen is encountered for the first time
- HAS MEMORY - responds more vigorously the second time a particular pathogen is encountered
What are the two branches of adaptive immunity?
- humoral (antibody mediated)
- cellular (cell-mediated)
What are antibodies (Ab) also called?
Immunoglobulins (Ig)
Glycoproteins are composed of 4 subunits.
What are they?
- 2 identical heavy chains
- 2 identical light chains
What does each antibody have?
- 2 identical antigen binding sites (Fab)
- 1 Fc site - can interact with other components of the immune system
- 5 classes of antibodies
Describe IgG (Immunoglobulin G)
- A monomer (aglutonates 2)
- Most abundant antibody in blood and tissues
- Most important for combating a pathogen
Describe IgM
- A pentamer (aglutonates 10)
- First antibody made when a new antigen is encountered
- Excellent at agglutination
- Does not leave blood and enter tissues
Describe IgA
- A dimer
- Secreted into saliva, tears, mucous
- Helps to protect mucosal surfaces
Describe IgD
- A monomer
- Found on surface of B cells
- Plays a role in activating B cells to respond against an antigen
Describe IgE
- A monomer
- Found of the surface of mast cells and basophils
- Causes them to release granules of histamine which triggers an allergic response
Antibodies have 5 major functions, what are they?
- Neutralization
- Osponization
- Agglutination
- Antibody mediated cytotoxicity
- Complement activation
Describe neutralization
- Ab stick to antigens on a foreign particle and block attachment sites
- Stops bacteria, viruses, and toxins from entering host cells.
Descrive opsonization
- Ab stick to a pathogen’s surface and flag down phagocytes
- Phagocyte interacts with the Fc region and engulfs the pathogen
- Greatly increases rate of phagocytosis
Describe agglutination
- Ab can stick to two identical antigens
- Bridges particles together in clumps
- Can be phagocytized more easily
Describe antibody mediated cytotoxicity
- Ab binds to antigen on the surface of a parasite
- Fc can interact with eosinophils
- Eosinophils release enzymes and reactive oxygen intermediates to attack the parasite
Describe complement activation
- Ab bound to a bacterial cell can activate complement (a set of proteins in the blood that assist other components of the immune system)
- Results in the membrane attack complex (MAC)
- Insert into bacterial membranes
- Forms a pore
- Cell leaks an dies
Adaptive response has 2 properties: Acquired and Specific. Describe them.
Acquired - a pathogen must be encountered before the adaptive immune response is mounted
Specific - can mount a directed attack against a specific pathogen. (Immunity of one pathogen does not confer immunity to another).
Define: memory
Once a specific pathogen has been encountered, immune system cells multiply and produce long living memory cells. If the pathogen is encountered again, the memory cells will mount a faster, stronger response.
Define: tolerance
Inability to mount an adaptive immune response against self-antigens. Immune system cells that recognize self-antigens are destroyed during development.
Define: primary response
The first time a new pathogen is encountered, the adaptive immune response is weak. The major result is the production of immunologic memory.
Define: secondary response
The next time that the pathogen is encountered, memory cells are ready to respond. Response can be so quick that the pathogen is unable to cause disease.. I.e. Immunity!!
Define: Immunogen
Any foreign particle that can induce an adaptive immune response. Normally large molecules such as proteins, polysaccharides, some lipids.
Define: antigen
Any substance that can react with antibodies or receptors on adaptive immune system cells.
Define: antibody
Protein made by the immune system that can bind to, and inactivate foreign antigens
Define: epitope (antigenic determinant)
- The actual part of the antigen that can bind to an antibody.
- The more epitopes on an antigen, the more immunogenic it will be and the more diverse population of antibodies that can be generated agains it.
Define: Hapten
Low molecular weight compound too small to be immunogenic on it’s own, but can be highly antigenic.
What is an example of a hapten?
Penicillin- is small and non-immunogenic on its own.
- Can bind to proteins in the blood forming a strong immunogen
- Antibodies are formed against it, leading to an allergic response
What are the 2 types of T lymphocytes?
- Tc cells (T-Cytotoxic cells)
- Th cells (T-Helper cells)
Describe Tc cells
- Destroy abnormal body cells (ex. cells infected by viruses)
- Involved in cell mediated response
Describe Th cells
- Help B and Tc cells prepare for an immune response
- Humoral and cell mediated
