Immunology 1 - Cells of the Immune System

Question 1

What are the soluble and cellular factors involved in innate immunity? [3]

Answer 1

1. soluble factors:
   
   • antibacterial factors
   • complement system
2. cellular factors:
   
   • scavenger phagocytes

Question 2

Antibacterial factors involved in innate immunity:

1. what are they? [2]
2. what type of molecule are each of them? [2]
3. where they can be found? [2]
4. their functions [3]

Answer 2

1. lysozyme
   
   • ​​enzyme
   • present at mucosal surfaces in respiratory and GI tract
   • active in breaking donw the gram positive cell wall
2. lactoferrin
   
   • ​​protein
   • found at mucosal surfaces in respiratory and GI tract
   • chelates iron → reduces soluble iron in GI/resp tract and therefore inhibiting the growth of bacteria

Question 3

Describe the complement pathways [7]

Answer 3

Question 4

Define opsonisation [1]

Answer 4

attracting immune cells and antibodies to the site

Question 5

What is the function of the following protein factors in complement:

1. C5? [1]
2. C3a? [1]
3. C3b? [1]

Answer 5

1. C5 causes formation of the membrane attack complex which disrupts cell membranes causing cell lysis and death
2. C3a causes recruitment of inflammatory cells
3. C3b causes opsonisation and phagocytosis

Question 6

Macrophages

1. difference between a monocyte and macrophage? [1]
2. macrophages in the liver are called? [1]
3. macrophages in the CNS are called? [1]
4. functions of macrophages? [3]

Answer 6

1. monocyte (blood) = macrophage (tissue)
2. Kupffer cells
3. microglia
4. functions:
   
   • phagocytosis
     
     • specialises in destruction of pathogens
   • antigen presentation
     
     • processes engulfed particles, travels to draining lymph nodes and presents to T cells in MHC II
   • cytokine production
     
     • M1, TNF-α etc. - inflammatory
     • M2, IL-10 etc. - regulatory

Question 7

What are the 3 functions of pattern recognition receptors? [3]

Answer 7

1. recognise molcules found commonly in microorganisms
2. able to recognise extracellular and intracellular threats
3. respond to bacteria, fungi and yeasts

Question 8

Neutrophils

1. functions of neutrophils? [3]
2. neutrophils die locally forming what? [1]

Answer 8

1. functions:
   
   • chemotaxis
     
     • migrate towards bacterial products, chemokines and danger signals
   • phagocytosis
     
     • ingest and destroy pathogens using proteases, reactive oxygen species, lysoszyme etc.
   • degranulation
     
     • releasing toxic granules extracellularly
2. they die locally producing pus

Question 9

Eosinophils

1. functions? [3]
2. they classically respond to which type of microorganism? [1]

Answer 9

1. functions:
   
   • chemotaxis
     
     • migrate in response to chemokines
   • degranulation
     
     • releasing toxic substances onto the surface of parasites
   • cytokine production
     
     • drives inflammation
     • production of IL-1, IL-2, IL-4, IL-8, TNF-α
2. classically respond to parasites

Question 10

Basophils/Mast cells

1. difference between basophils and mast cells? [1]
2. where are mast cells usually found guarding? [1]
3. play an important role in what condition? [1]
4. functions of basophils/mast cells? [2]

Answer 10

1. basophils (blood) = mast cells (tissues)
2. guarding mucosal sites
3. play an important role in allergy
4. functions:
   
   • degranulation
     
     • ​rapidly releasing pre-formed granules containing cytokines and mediators (e.g. histamine)
   • cytokine release
     
     • store many pre-formed cytokines that are ready for release that attract and drive the immune response

Question 11

Describe the 3 functions of dendritic cells [3]

Answer 11

1. phagocytosis
   
   • not as much as macrophages, dendritic cells are more APCs
2. migration
   
   • sit in tissues constantly sampling the environment
   • when activated, will travel to draining lymph nodes
3. antigen presentation (APCs)
   
   • presents to CD4 T cells
   • initiates adaptive immune response

Question 12

Adaptive Immunity

1. describe the humoral adaptive response [2]
2. describe the cellular adaptive response [4]

Answer 12

1. humoral adaptive response
   
   • B cells
     
     • release antibodies (immunoglobulins) that kill extracellular pathogens (e.g. bacteria)
2. cellular adaptive response
   
   • CD4 T cells
     
     • helper T cells
     • directs B cells and CD8 T cells
     • increases cytokine secretion
   • CD8 T cells
     
     • killer/cytotoxic T cells
     • targets intracellular pathogens (e.g. viruses)

Question 13

Label the structures of an antibody on the following diagram: [4]

Answer 13

Question 14

What are the 3 functions of antibodies? [3]

Answer 14

1. opsonisation for phagocytosis
2. activation of complement for lysis
3. neutralisation of toxins and pathogen binding sites

Question 15

1. How do antibody isotypes differ structurally? [1]
2. Describe the features of the following antibody isotopes:
   
   • IgM [3]
   • IgG [4]
   • IgA [3]
   • IgE [2]

Answer 15

1. differ in Fc regions
2. lgM:
   
   • main antibody of primary immune response
   • low affinity
   • activates complement
3. lgG:
   
   • main antibody of secondary immune response
   • higher affinity as part of secondary response
   • Activates Complement
   • binds Fc𝛾 receptor on phagocytes (opsonsises).
   • crosses placenta
4. lgA:
   
   • “antiseptic paint”
   • present in secretions and lines epithelial surfaces
   • neutralises by blocking binding of pathogens
5. lgE:
   
   • high affinity binding to mast cells through Fc receptor
   • role in allergy

Question 16

Optimal B cell response requires T cell help. What do T cells assist with? [5]

Answer 16

1. clonal expansion of specific B cells
2. progression to antibody secreting cells (plasma cells)
3. progression to memory B cells
4. isotype switching to IgG, IgA and IgE
5. affinity maturation

Question 17

Describe the T Cell Receptor (TCR) and what it recognises [3]

Answer 17

1. the receptor is on the surface of T cells and only recognises antigens when it is presented in a MHC molecule
2. recognises short peptide lengths

Question 18

How is autoimmunity prevented? [3]

Answer 18

1. B cells develop in the bone marrow and if B cell receptor binds strongly to “self” antigen in bone marrow, the cell will die by apoptosis
2. T cells originate in bone marrow and migrate to thymus, and if T cell receptor binds strongly to “self” antigen in thymus, the cell will die by apoptosis
3. activation of both cell types requires presence of danger signals to activate. if antibody/TCR engaged in absence of “second signal”, then cell likely to become anergic

Question 19

Describe the differences between MHC Class I and MHC Class II under the following headings:

1. What type of T cell it presents to
2. What type of cell it is found on
3. What type of antigen it presents

Answer 19

• Class I MHC
  
  1. ​​presents to CD8 T cells
  2. found on all nucleated cells
  3. presents intracellular antigen
• Class II MHC
  
  1. presents to CD4 T cells
  2. found on antigen presenting cells
     
     • (dendritic cells, macrophages, B cells)
  3. presents extracellular derived antigen

Question 20

Organs of the Adaptive Immune System

1. What are the primary organs and their functions? [4]
2. What are the secondary organs? [4]

Answer 20

1. primary organs:
   
   • thymus - T cell education
   • bone marrow - B cell education
2. secondary organs:
   
   • lymph nodes
   • spleen
   • mucosal associated lymphoid tissue of GI tract (MALT) or the bronchial tract (BALT)

Question 21

Lymph Nodes

1. location of B cells? [1]
2. location of T cells? [1]
3. location of macrophages and plasma cells? [1]

Answer 21

1. primary lymphoid follicle
2. paracortical areas
3. medullary cords

Question 22

What are the functions of the spleen? [2]

Answer 22

1. filters blood of senescent cells and blood borne pathogens
2. important in response to encapsulated organisms and blood borne pathogens

Question 23

What are the 4 functions of the adaptive immune system? [4]

Answer 23

1. provides specific antibodies to the innate immune system to enhance pathogen clearance
2. provides cytokines to the innate immune system to upregulate activity
3. finishes off the job of clearing pathogens
4. develops a memory to prevent future infection

Question 24

Describe the secondary response to an infection [4]

Answer 24

1. memory B cells and memory T cells already present at a high frequency
2. memory lymphocytes have lower threshold for activation and actively patrol the sites of previous pathogen entry
3. preformed antigen specific lgA prevents pathogen binding
4. preformed high affinity lgG rapidly opsonises pathogen for phagocytosis