8: Immunology: The Lymphatic System and Innate Immunity

Question 1

Pathogenesis

Answer 1

The manner of development of a disease

Question 2

Innate Immunity

Answer 2

• Present at birth
• Provides immediate protection
• Is general in action
• First and second lines of defence

Question 3

Adaptive Immunity

Answer 3

• Recognises specific antigens
• Is systemic in action
• Has a memory

Question 4

Immune Function of the Lymphatic System

Answer 4

• Some fluid is lost from blood through capillary beds
• Lymphatic capillaries absorb this fluid (lymph) and any particles within it
• Lymph is returned to the blood and ‘filtered’ via the lymph nodes

Question 5

First Line of Defence

Answer 5

• Barriers: skin and mucous membranes

- Associated secretions and mechanisms

Question 6

Second Line of Defence

Answer 6

• Anti-microbial proteins
• Inflammation and fever
• Leukocytes

Question 7

Lysozymes

Answer 7

• Digest the bacterial cell wall
• Secreted in tears, mucous, and saliva
• Lysozymes break down peptidoglycan of bacterial cell wall

Question 8

Interferons

Answer 8

• Proteins secreted by virally infected cells
• Help protect neighbouring cells by:
  > Block viral protein synthesis
  > Degrade viral DNA

Question 9

The Complement System

Answer 9

There is a number of proteins that are circulating around in the blood. When activated, they get together and connect to form the complement system. As a result of this, it aids the immune system primarily by opsonisation (enhances phagocytosis and inflammation).

Question 10

How Do These Proteins ‘Complement’ the Immune Response?

Answer 10

By:

• Promoting the release of histamine by mast cells and basophils
• Binding to antigen and facilitating phagocyte binding – opsonisation
• Also induce cell lysis on their own by forming a Membrane Attack Complex (MAC)

Question 11

Inflammation: Four Cardinal Signs

Answer 11

• Heat
• Redness
• Swelling
• Pain - loss of motion

Question 12

Function of Leukocytes

Answer 12

Function by:

• Phagocytosis
• Destroying abnormal or infected cells
• Producing and amplifying inflammation

Question 13

Phagocytes: Neutrophils

Answer 13

Phagocytosis and activation of bacterial mechanisms

Question 14

Phagocytes: Macrophages

Answer 14

• Phagocytosis and activation of bactericidal mechanisms

- Antigen presentation

Question 15

Natural Killer (NK) Cells

Answer 15

• Patrol blood and lymph
• Destroy cancer & virus-infected cells
• Detect abnormal cell-surface molecules
• Kill cells by bombarding them with perforin and granzyme
• Can also promote inflammation

Question 16

Humoral Immunity (B Cells)

Answer 16

• Antibody-mediated immunity
• Immune function performed by antibodies
• Eliminates extracellular pathogens

Question 17

Cellular Immunity (T Cells)

Answer 17

• Cell-mediated immunity
• Immune function performed by activated cells
• Eliminated intracellular pathogens, cancerous cells, and foreign cells (organ transplant)

Question 18

Antigens

Answer 18

Induce a specific immune response

Question 19

Epitopes

Answer 19

Specific areas of an antigen recognised by cells of adaptive immunity

Question 20

Self-Antigens

Answer 20

• Our cells display various ‘self-antigens’, recognised by our immune system
• They include MHC molecules

Question 21

Class I MHC (Own Cells)

Answer 21

• Displayed by all nucleated cells
• Incorporate foreign antigen after infection
• Labels cells as infected to Cytotoxic T Cells

Question 22

Class II MHC (Antigen-Presenting Cells)

Answer 22

• Displayed by APCs
• Engulf and break down pathogenic antigen
• Present antigen-MHC to T Cells

Question 23

B Cells

Answer 23

• When activated, they produce plasma cells

Question 24

T Cells

Answer 24

• Main effector cell is the cytotoxic T cell

- Destroys infected/abnormal cells

Question 25

T Cells Possess Two Major Surface Proteins

Answer 25

- T Cell Receptors (TCRs): each individual cell has thousands, but all bind to the same antigen, different from one T cell to the other - CD proteins: bind to MHC proteins on other cells (CD4 and CD8)

Question 26

Helper T Cells

Answer 26

- Coordinate and activate humoral and cellular divisions of adaptive immunity - Express TCRs and CD4 proteins on surface - CD4 binds to MHC Class II – they present to the T Cells the antigen which orchestrates the immune response

Question 27

Cytotoxic T Cells

Answer 27

- Destroy infected or abnormal/cancerous cells - Express TCRs and CD8 proteins on surface - CD8 binds to MHC Class I

Question 28

T Cell Activation

Answer 28

- Activation starts when T Cells bind to antigen on MHC molecules using their TCR - CD4 or CD8 must also bind to MHC - Once activated, T Cells undergo clonal selection – produce identical copies - Produce effector cells and memory cells

Question 29

Helper T Cells (CD4)

Answer 29

- Recognise antigens on Class II MHC - Help with the activation of other immune cells - Produce chemical messengers called cytokines

Question 30

Cytotoxic T Cells (CD8)

Answer 30

- Very mobile – leave lymphatic tissue - Recognise antigens on Class I MHC, signalling infected/defective cell - Bind to infected cells and destroy them

Question 31

Memory T Cells

Answer 31

- Produced during T Cell activation - Remain in lymphatic tissue - Very fast reaction upon second exposure to the same antigen

Question 32

B Cell Activation: Plasma Cells

Answer 32

- Secrete antibodies – 2000/sec/cell - Last approx. 4-5 days - Peak plasma antibody concentration at 10 days

Question 33

Memory B Cells

Answer 33

- Remember the antigen for future rapid activation | - Vaccines