8 - Human Immune System

Question 1

What are the cellular components of blood

Answer 1

RBC
WBC
Platelets (thrombocytes)

Question 2

RBCs

Answer 2

Transport oxygen; haematocrit = % of blood volume made up by RBCs

Question 3

WBCs

Answer 3

Immune response; granular and agranular leukocytes

Some circulate, some are tissue-resident

Question 4

Platelets (thrombocytes)

Answer 4

Blood clotting

Question 5

What are the soluble components of blood (4)

Answer 5

Plasma proteins (albumins, globulins)

Clotting factors (fibrinogen)

Cytokines and chemokines (signalling molecules)

Complement proteins (part of innate immunity)

Question 6

What is haematopoiesis

Answer 6

Development of blood cells from pluripotent stem cells in bone marrow

Question 7

What does haematopoiesis involve

Answer 7

Lymphoid stem cells → lymphocytes
Myeloid stem cells → all other blood cells

Question 8

What is haematopoiesis regulated by

Answer 8

Regulated by cytokines, growth factors, and oxygen levels

Question 9

What are the two main types of pathogens based on location

Answer 9

Extracellular: Easier to detect and kill
Intracellular: Hide within host cells, harder to detect

Question 10

How does infection impact populations in developed vs. developing countries

Answer 10

Developed countries: <2% of deaths from infection, but newborns and elderly are more vulnerable

Developing countries: Account for 70–80% of deaths; parasitic diseases are common

Question 11

What are the physical barriers to infection (5)

Answer 11

Skin: Thick keratinised layer

Mucous membranes: Trap pathogens in respiratory/digestive tracts

Tears & saliva: Contain antimicrobial lysozyme

Stomach acid: Kills ingested pathogens (low pH)

Normal flora: Competes with pathogens

Question 12

What are the 3 major sources of infection and their defences

Answer 12

Digestive tract: Salivary lysozyme, stomach acid, normal flora

Urogenital tract: Acidic urine, normal flora

Respiratory tract: Ciliary action

Question 13

What are the key cells of the innate immune system (4)

Answer 13

Neutrophils

Macrophages

Dendritic cells

Natural Killer (NK) cells

Question 14

Neutrophils

Answer 14

Phagocytose pathogens

Question 15

Macrophages

Answer 15

Engulf and digest microbes

Question 16

Dendritic cells

Answer 16

Present antigens to T cells

Question 17

Natural Killer (NK) cells

Answer 17

Destroy infected/tumour cells

Question 18

What are the soluble proteins in the innate immune system (3)

Answer 18

Complement proteins

Interferons

Cytokines

Question 19

Complement proteins

Answer 19

Enhance phagocytosis and lysis

Question 20

Interferons

Answer 20

Inhibit viral replication

Question 21

Cytokines

Answer 21

Mediate inflammation and signalling

Question 22

What are the anti-microbial functions of innate immune cells (5)

Answer 22

Recognise PAMPs via TLRs → signal transduction

Non-specific defensive molecules (e.g. defensins, ROS, HOCl, H₂O₂, proteases)

Interferons & cytokines

Inflammatory response

Complement activation

Question 23

What is opsonisation

Answer 23

Pathogens coated with opsonic proteins (e.g. C3b)

Question 24

Opsonisation importance

Answer 24

Recognised more easily by phagocytes → enhanced pathogen clearance

Question 25

What are the steps of phagocytosis

Answer 25

1. Recognition of bacteria 2. Pseudopodia formation 3. Engulfment into phagosome 4. Granule contents secreted into vesicle 5. Toxic products destroy bacteria

Question 26

What are NETs

Answer 26

Neutrophil Extracellular Traps (NETs): DNA-protein webs released during inflammation

Question 27

NETs function + how they are triggered

Answer 27

Triggered by ROS production Trap pathogens and prevent spread

Question 28

What is the role of eosinophils

Answer 28

Defence against parasites like nematodes Secrete toxic proteins, lysozymes, ROS, leukotrienes, and prostaglandins

Question 29

What’s the difference between monocytes and macrophages

Answer 29

Monocytes: Immature cells in blood Macrophages: Mature tissue phagocytes, involved in chronic inflammation/infection

Question 30

What is the function of Natural Killer (NK) cells

Answer 30

Cytotoxic cells that kill virus-infected or tumour cells Respond to chemical signals from infected cells

Question 31

What are the steps of the inflammatory response

Answer 31

Tissue injury triggers histamines and cytokines Vasodilation increases blood flow Vascular permeability increases → immune cells enter tissue Phagocytes migrate (chemotaxis) Pathogens cleared, tissue repair begins

Question 32

What are the pathways of complement activation

Answer 32

Classical Alternative

Question 33

Classical activation

Answer 33

C1 binds antibodies on pathogen → cascade → C3b opsonin or MAC formation

Question 34

Alternative activation

Answer 34

Doesn’t need antibodies; C3b accumulates directly on pathogen surface

Question 35

What are the key cells in the adaptive immune system

Answer 35

B cells: Produce antibodies T cells: Helper (CD4+) / Cytotoxic (CD8+)

Question 36

What are the soluble proteins in the adaptive immune system

Answer 36

Antibodies (Immunoglobulins): Bind to antigens Cytokines: Support both humoral and cell-mediated responses

Question 37

Antigen meaning

Answer 37

A molecule that triggers an immune response

Question 38

Epitope

Answer 38

Specific region of an antigen recognised by immune system

Question 39

What are the key features of adaptive immunity (3)

Answer 39

Specificity for antigen Diversity of antigen recognition Memory: Faster response upon re-exposure

Question 40

What is clonal expansion of lymphocytes

Answer 40

1. Antigen recognition 2. Activation & proliferation of lymphocytes 3. Production of effector and memory cells 4. Enhanced response upon re-exposure