Unit5 Understanding - Immunology & Vaccines

Question 1

Explain how physical and chemical barriers protect us from infection.

Answer 1

Physical barriers, such as skin and mucous membranes, defend the body from microorganisms being able to enter or neutralize them before infection can begin. Chemical barriers, such as the secretions of glands, remove organisms if they are able to enter the body or combat them while inside the body and attempt to slow or contain infections.

Question 2

List and describe 4 characteristics of skin that protect us from microbial invasion.

Answer 2

The skin and its antimicrobial features is the most important defense. It is thick, with closely packed cells, forming a continuous layer and the dermis is interwoven with connective tissue. Keratin is tough protein that is packed in bundles and indigestible to most microbes. The skin sheds with the surface layer (epidermis) drying, dying and falling off. Lastly, the pH of the skin is between 3 to 5 due to fatty acid and lipid secretion. This low pH is inhibitory for most microbes, especially gram-negative microbes.

Question 3

Describe the role of normal flora in protecting us from infection.

Answer 3

The normal flora is not part of the innate immune system but they provide incredible protection and resistance to disease. Normal flora have a competitive advantage over pathogenic microbes in competing for nutrients and space because they are well adapted to a number of attachment sites in which they live. They also produce substances that inhibit or kill pathogens. The development of the immune system is reliant on the presence of microbiota even before birth.

Question 4

What is lysozyme? Where is it found, and what is its function?

Answer 4

Lysozyme is a large enzyme capable of breaking down cell walls of mostly G+ bacteria and some G- bacteria. It is found almost all secretion such as tears, saliva, nasal secretions, tissue fluids, perspiration, breast milk and urine. Lysozyme’s ability to break the peptide bonds between the sugars of peptidoglycan destroys cell walls of mostly G+ bacteria because their peptidoglycan layer is exposed.

Question 5

Be able to describe the organs and cells that make up the immune system.

Answer 5

The key primary lymphoid organs of the immune system include the thymus and bone marrow, as well as secondary lymphatic tissues including spleen, tonsils, lymph vessels, lymph nodes, adenoids, skin, and liver. Bone marrow contains stem cells which give rise to all blood cells; B cells mature in bone marrow. The thymus is the site of T cell maturation. The lymph node contains large amounts of lymphocytes and phagocytic cells and the lymph vessels carry antigens and cell to the lymph node to activate an immune response. Tonsils perform similar tasks by draining to nearby lymph nodes.The spleen contains lymphocytes and macrophages to monitor blood for microbes and impurities. Peyer Patches are lymphoid tissue of the small intestine that performs antigen sampling.

Question 6

List and describe the functions of the cells that make up the immune system.

Answer 6

Neutrophils phagocytize and engulf bacteria and fungi. Eosinophils participate in inflammatory reaction and kill parasite with oxidative burst. Basophils release histamine and other inflammation-inducing chemicals. Monocytes phagocytize and digest engulfed materials. They are the precursor to macrophages. Macrophages can be fixed or wandering and they perform phagocytosis and and cause inflammation.

Question 7

What are lymph nodes and why are they important for immune system function?

Answer 7

Lymph nodes are small, round organs that filter out bacteria, waste and other toxins. They are the major site of B and T cells, lymphatic vessels and the site where antibodies bind to antigens. They are important for proper function of the immune system acting as filters for foreign particles and cancer cells. They become inflamed or enlarged in response to various infections.

Question 8

Explain Peyer Patches.

Answer 8

Peyer Patches, or GALT, are large aggregations of gut-associated lymphoid tissue in the small intestine. They perform antigen sampling to help keep the immune system ready to respond to an infection quickly. They also constantly sample the normal flora so the body learns to tolerate it and doesn’t attack it.

Question 9

What is hematopoiesis?

Answer 9

Hematopoiesis is the production of all of the cellular components of blood and blood plasma. It occurs within the hematopoietic system, which includes organs and tissues such as the bone marrow, liver, and spleen. Simply, hematopoiesis is the process through which the body manufactures blood cells.

Question 10

Describes the steps in phagocytosis.

Answer 10

The first step is chemotaxis where phagocytic cells are recruited to the site of injury or infection by cytokines, C5a, microbial molecules and cellular debris. Second is adherence in which microbes attach to Toll-like receptors on the surface of phagocytic cells, initiate phagocytosis, produce cytokines and recruit more phagocytes. Engulfment is when the microbe is endocytosed forming the membrane-bound phagosome in the process. In digestion, phagosomes and lysosomes merge exposing the microbe to acid, hydrolytic enzymes and toxic oxygen product. The resulting waste is expelled via exocytosis.

Question 11

What are Toll-like receptors and how do they work?

Answer 11

Toll-like receptors are “pattern recognition” receptors on cells that detect common microbial molecules to induce phagocytosis and to cause the cell to produce cytokines that recruit more phagocytes.

Question 12

Describe the stages of inflammation including the cells and molecules involved

Answer 12

1. Damage to tissues or cells or detection by toll-like receptors causes release of cytokines.
   
   2. TNF-alpha stimulates production of acute-phase proteins produced by the liver.
   3. Chemokines and proinflammatory molecules attract phagocytic cells to the site of injury (chemotaxis).
   4. Clotting can be utilized to localize and contain the injury by blocking vessels and sealing off the wound.
   5. Phagocytic cells (neutrophils and monocytes) stick to the capillary walls near the injured area (margination).
   6. The phagocytes squeeze through the capillary endothelium (diapedesis) and into the afflicted area where they ingest microbes, damaged cells, and debris (phagocytosis).
   7. Tissue repair cells of the parenchyma and stroma reconstruct the damaged area.

Question 13

Describe the complement cascade and the outcomes of complement activation.

Answer 13

The complement cascade is more than 30 blood serum proteins which function to destroy microbes by three activation pathways (alternative, classical and lectin). The most important of the complement cascade is C3. The outcomes are opsonization, which promotes attachment of a phagocyte to a microbe and enhances phacytosis, Inflammation, and cytolysis which bursts the microbial cell.

Question 14

Explain how interferon functions to protect cells from infection.

Answer 14

When cells are side by side and one is an RNA virus, it causes interferon to produced which produce anti-viral proteins (AVP) to block viral replication in neighboring cells and induces apoptosis, completely diminishing the virus.

Question 15

Describe and compare humoral and cellular immunity.

Answer 15

Humoral and cellular immunity are types of adaptive immunities. Humoral immunity involves B lymphocytes and is effective against antigens in the circulation. Cellular immunity involves T cells and eliminates infected or abnormal cells.

Question 16

Describe the structure and function of antigens.

Answer 16

Antigens are molecules capable of producing an immune response. The best antigens are proteins because they are large and complex. Antigens have epitopes, which are the portion of the antigen that is recognized by the antibody. They also have haptens, which are substances of low molecular mass that it too small to cause a formation of antibodies but can do so when combined with a carrier molecule.

Question 17

Describe the structure and function of antibodies.

Answer 17

B cells produce antibodies which are either secreted or found on the surface. They contain a variable region which is responsible for antigen binding and a constant region, which has binding sites for phagocytic cells and complement.

Question 18

Explain the process by which the B-cell repertoire is produced and dangerous B-cells are destroyed.

Answer 18

The B cell repertoire forms in the bone marrow and produce huge numbers of different antibodies with the ability to bind a number of different antigens. The antibody genes recombine randomly such that each B cell produces and antibody with a unique antigen-binding capability. Dangerous B cells are destroyed by clonal deletion.

Question 19

Describe the processes of clonal selection and B-cell activation.

Answer 19

B cells are activated to produce antibody when it binds to an antigen and gets help from a T cell. Only B-cells which bind antigen are activated to divide and eventually make plasma cells and memory cells. Somatic hypermutation occurs during this process resulting in antibodies with high affinity for the antigen. Through mutating and memory cells, long lasting immunity occurs.

Question 20

Describe the potential outcomes of antibody-antigen binding.

Answer 20

• opsonization: antibodies enhance phagocytosis
  
  • activation of complement: causes inflammation and cell lysis
  • agglutination: reduces # of infectious units to be dealt with
  • neutralization: blocks adhesion of bacteria and viruses to the mucosa and blocks the attachment of toxin
  • ADCC: antibodies attached to target cells cause destruction by eosinophils and NK cells

Question 21

Compare and contrast the functions of CD4 and CD8 T-cells.

Answer 21

Helper T cells (CD4) are the central controllers of immune response and activate and control both humoral and cellular immunity. They can differentiate into subtypes (TH1, TH2, THF, etc) which secrete different cytokines to facilitate different types of immune response. Cytotoxic T Cells (CD8) are a specialized T cell that destroys abnormal or infected cells.

Question 22

Describe antigen processing and presentation and explain why it is critical for immune system function.

Answer 22

The most important antigen-presenting cells are dendritic cells, macrophages and B cells. The APC phagocytes an antigen, the antigen is process into 10-20 amino acid fragments which are then combined with MHC molecules located on the cell surface. The MHC-peptide combo is then presented to a T cell. This is important in identifying and destroying a pathogen.

Question 23

Be able to explain how T-cells are activated.

Answer 23

t cells require 2 signals for activation. First signal is antigen presentation by dendritic cells and other APC’s which collect and present the antigen. Second signal is constimulation, where a toll-like receptor on a dendritic cell or other APC is bound and causes a production of a constimulatory molecule. Activated T cells are important because T helper cells activate the other portions of the immune system.

Question 24

What is clonal deletion of B and T-cells? Where does it occur and why is it important?

Answer 24

Clonal deletion is a process by which B cells and T cells are deactivated after they have expressed receptors for self-antigens and before they develop into fully immunocompetent lymphocytes. Immune system cells, such as T cells and B cells, have proteins on their surface that allow them to recognize foreign invaders and attack them. Areas on these proteins can vary from cell to cell, allowing them to react to a variety of threats. Occasionally, T cells and B cells are produced that react to proteins that are expressed by the body’s own cells, called autoantigens. Clonal deletion is a process that allows these cells to be neutralized before they are released into the body, where they could potentially begin attacking healthy tissue. Clinical deletion of B cells happens in the bone marrow and while T cells originate in the bone marrow, they mature in the thymus and it is here where clinical deletion of T cells occur.

Question 25

Explain why T-helper (CD4) cells are called the “central regulators of the immune system”.

Answer 25

T helper cells can recognize an antigen presented on the surface of a macrophage and activate it, making the macrophage more effective in both phagocytosis and in antigen presentation. They can also differentiate into subtypes (TH1, TH2, THF) which can secrete different cytokines to facilitate different types of immune response.

Question 26

Describe the types of immunity and be able to give an example of each. (e.g. natural acquired passive immunity)

Answer 26

Naturally-acquired active immunity: antigens enter body naturally
Naturally-acquired passive immunity: mother to fetus
Artificially-acquired active immunity: antigens produced by vaccines
Artificially-acquired passive immunity: preformed antibodies in immune serum introduced into the body by injection

Question 27

Explain the principle of vaccination.

Answer 27

Vaccines contain part or whole of the pathogenic microbe and they can be alive or dead. They are introduced into the body to induce a specific immune response to provide long-term protection against a particular pathogen by the body building immunity to it by producing antibodies without actually causing the person to have disease.

Question 28

Describe and compare the types of vaccines.

Answer 28

Attenuated live vaccines contain live, weakened versions of the pathogen. The weakened microbe can replicate, but cannot cause illness and evoke a strong immune response with production of high affinity antibodies and memory B and T cells. Inactivated whole vaccines contain microbes that have been killed by chemicals or heat. the dead microbes cannot replicate or change back to their disease-causing state. Although it is safer, it does not produce as strong of an immune response as an attenuated vaccine. Subcellular contain toxoids and antigenic fragments of the microbe and are similar to inactivated vaccines in that they are safe but don’t produce a strong immune response as a live vaccine.

Question 29

Discuss vaccine safety and herd immunity.

Answer 29

Vaccines are safe and the possible side effects of the vaccine are safer than that of actually developing the disease. Herd immunity is the inability of a disease to spread within a population because of the lack of susceptible hosts who have been vaccinated.

Question 30

Describe the connection between vaccination and primary and secondary immune responses.

Answer 30

After immunization, the vaccine induces the humoral immunity system to proliferate more B cells and again to memory and plasma B cells. Plasma cells produce antibodies against the vaccines and it takes time to react. As the plasma cells die the immune response also reduces. In secondary immune response, the reaction will be much faster, higher and it stays for a longer time. In secondary immune response memory B cells responds to the vaccines. And here the memory B cells will be more than naive B cells. There will be a larger number of plasma cells and antibody production will also be very high.

Question 31

What is serology and serological testing.

Answer 31

Serology in the study of an in-vitro antibody-to-antigen interactions. Serological testing tests the blood for the presence of antibodies for a specific pathogen.

Question 32

Explain how monoclonal antibodies are made and how they are useful.

Answer 32

Monoclonal antibodies fuses an antibody-secreting B-cell and myeloma (tumor) cell to form an “immortal” hybridoma. Hybridomas secrete large amounts of specific, identical antibodies termed monoclonal antibodies. They are useful in tissue typing, identification of microorganisms and disease diagnostics as well as therapeutics.

Question 33

Compare monoclonal and polyclonal antibodies.

Answer 33

Monoclonal antibodies are produced by hybridomas which secrete large amounts of one, specific antibody. Polyclonal antibodies are made by immunizing an animal with an antigen and then collecting serum. Serum with contain a mix of different antibodies that together recognize many epitopes on the immunizing agent and is relatively inexpensive to produce.