Immunology

Question 1

what are the main types of host defence

Answer 1

1. intrinsic - always present and can be physical or chemical
2. innate - induced by an infection e.g. interferon, cytokines, macrophages etc.
3. adaptive - is tailored to a specific pathogen – T and B cells.

Question 2

what is the difference between innate and adaptive immunity

Answer 2

innate you are born with and adaptive you acquire

Question 3

what are the 2 main effectors in innate immunity

Answer 3

• specialist macrophages [kupffer cells, dendritic cells, alveolar macrophages]
• neutrophils

Question 4

what are the precursor of alveolar macrophages

Answer 4

monocytes

Question 5

what are neutrophils

Answer 5

a type of WBC

Question 6

where are neutrophils made

Answer 6

in the bone marrow, making the myeloid cells.

Question 7

what is a key component of neutrophils that helps with their function

Answer 7

• They contain granules:
  
  • PRIMARY – myeloperoxidase, elastase, cathepsins, defensins
  • SECONDARY – receptors, lysozyme, collagenase

Question 8

neutrophils are not involved in inflammation - T/F

Answer 8

False

• neutrophils participate in the inflammatory response and protect against infection
• They are present in blood at all times but are only activated when needed → generation of ROS
• as the insult is removed and healing begins, the inflamm cells must be removed via
  
  • exudate
  • migration
  • apoptosis

Question 9

what are the 7 functions of neutrophils

Answer 9

1. identification of pathogen
2. activation
3. adhesion
4. chemotaxis / migration
5. phagocytosis
6. bacterial killing -
   
   1. achieved via enzymes and ROS generation by NADPH oxidase complex
7. apoptosis

Question 10

which cells mediate adaptive immunity and by what mechanism?

Answer 10

• B cells by humoral responses
• T cells by cell-mediated responses

Question 11

what is an antigen

Answer 11

• a molecule able to induce a specific immune response from the host.
  
  • Can be proteins, polysaccharides, lipids, DNA etc.

Question 12

what is an epitope

Answer 12

One antigen can have different epitopes – recognisable regions of the antigen

Question 13

what are the 4 main types of T-cells

Answer 13

1. Cytotoxic T-cells
2. T-helper cells
3. T-regulatory cells
4. Memory T- cells

Question 14

where are B and T cells made and where do they mature?

Answer 14

• B cells:
• made in the bone marrow
• maturation begins in the bone marrow and ends in the spleen, lymph nodes
• T cells
• made in the bone marrow
• Mature in the thymus

Question 15

what are 3 key functions of adaptive immunity?

Answer 15

1. specificity and diversity
2. self- tolerance - recognition of self-antigens and elimination of autoreactive clones
3. memory via signature BCRs and TCRs.

Question 16

In what form do T and B cells recognise antigens?

Answer 16

• B cells
• B cell receptors recognise antigens in the native form AND when presented by antigen presenting cells.
• T cells recognise antigens presented on MHCs on APCs
  
  • APCs include: dendritic cells, macrophages, B cells

Question 17

what is an antibody

Answer 17

a protein with a constant and a variable region

Question 18

describe cell-mediated immunity

Answer 18

t-cells can have CD4 or CD 8 expression

• CD8
• a cell that is infected presents the pathogen’s antigen on its surface via an MHC1 molecule
• T-cells that fit the antigen, with CD8 expression, encounter and bind to MHC1 presenting cells
  
  • all nucleated cells have MHC1
• this → activation of the T-cell → CD8 cytotoxic T-cell response.
• CD4
• an antigen presenting cell encounters a pathogen and presents the antigen on its surface via MHC2
• the APC travels to the lymph node and presents to a matching T-helper cell with CD4 expression
• this binding → activation and multiplication of the T-cells
• T-helper cells and CD4 cytotoxic T-cells are produced
  
  • the helper cells
    
    • help B cells produce antibodies
    • form memory T-cells
    • form Regulatory T-cells to stop immun overreaction and help identify self-antigens

Question 19

Describe Humoral immunity

Answer 19

1. the pathogen’s antigen binds to a matching BCR either in its native state or via and APC.
2. the antigen is then taken up into the B cell by endocytosis and the antigen is presented on its surface via MHC2
3. a follicular T-helper cell with a matching TCR binds to the antigen presented on MHC2 on the B-cell → activation of the follicular T-cell → production of helper factors
4. helper factors activate the B-cell → plasma cell formation and memory B-cell formation.

Question 20

how are such variable BCRs and TCRs created

Answer 20

• VDJ gene recombination
  
  • Variable, Diversity, Joining segments
• this recombination process is very random → ⇡ diversity.

Question 21

what is somatic hypermutation and where does is occur?

Answer 21

• after a matching BCR binds to an antigen it proliferates.
• during proliferation loads of mutations occur in the binding regions of the BCR to increase affinity for the antigen → more efficient antibodies.
• only occurs in B cells

Question 22

what is immune tolerance and how is it mediated?

Answer 22

• immune tolerance is the bodies ability to not respond to the adaptive immunity system to avoid an overreaction.
• T-reg cells are responsible for this by killing immune cells with receptors capable of binding to self-cells.

Question 23

how many hypersensitivity classes are there?

Answer 23

4

1. Type 1: Allergy, anaphylaxis and atopy – IgE dependent acute response
2. IgG binding to self antigens (autoimmune)
3. immune complex diseases
4. delayed type hypersensitivity reaction

Question 24

describe a type 1 hypersensitivity response

Answer 24

• Type 1: Allergy, anaphylaxis and atopy – IgE dependent acute response
• involved in conditions such as asthma, eczema and hay fever
• IgE causes release of histamine from mast cells by activating FcεR1 receptor. → vasodilation and opening up of gap junctions
• treated with antihistamines, steroids and avoiding triggers
  
  • effects seen immediately - within an hour

Question 25

describe a type 2 hypersensitivity response

Answer 25

**IgG binding to self antigens (autoimmune)** * cytotoxic * the immune system attack the body's own cells * e.g. * effect seen in hours - days

Question 26

Describe a type 3 hypersensitivity response

Answer 26

**Immune complex disease** * A large scale immune response * complexes of IgG precipitate and can't be cleared by macrophages * e.g. Farmers lung * effects seen within 7-10 days

Question 27

describe a type 4 hypersensitivity response

Answer 27

**delayed hypersensitivity reaction** * Type IV hypersensitivity is a T-cell-mediated hypersensitivity, meaning the inflammation and potential tissue damage is caused by either T helper cells (CD4+) or cytotoxic T cells (CD8+). * antibodies are not involved * e.g. tuberculosis * effects seen in day - weeks - months

Question 28

characteristics of IgG

Answer 28

* most abundant antibody/ immunoglobulin * acts as an opsonin - binds to the pathogen and signals phagocytes towards it for phagocytosis

Question 29

characteristics of IgA

Answer 29

* found on the mucosa surface * prevents pathogens from entering the body

Question 30

characteristics of IgE

Answer 30

* involved in type 1 hypersensitivity reactions * seen in asthma, atopic dermatitis and hayfever

Question 31

characteristics of IgM

Answer 31

* **IgM** is the first antibody secreted by the adaptive immune system * it activates complement * doesnt require t-cell help

Question 32

characteristics of IgM

Answer 32

* **IgM** is the first antibody secreted by the adaptive immune system * it activates complement * doesnt require t-cell help

Question 33

Characteristics of IgD

Answer 33

* helps mature B cells leave the bone marrow