Innate immune response

Question 1

What are the proportions of leucocytes in the blood?

Answer 1

Less than 1%
60- neutrophils
25- B and T lymphocytes
5- monocytes
rest (5) eosinophils and basophils

Question 2

What is complement activation?

Answer 2

Series of soluble proteins in the blood
C1 to C9
Acellular, circulate in inactive state

Question 3

What are the pathways of activation of complements?

Answer 3

Classical
Mannose-binding lectin
Alternative

Question 4

What is the classical pathway of complement activation?

Answer 4

Only occurs when there are antibodies specific to foreign antigen present (adaptive)
Antibody complexes bound by complement component C1q
Activate subsequent complement components

Question 5

What is mannose-binding lectin pathway of complement activation?

Answer 5

Activation through mannose-binding lection binding mannose/ similar carbohydrates on bacteria- PRR like
Mannose not present on surface of host cells

Question 6

What is alternative pathway of complement activation?

Answer 6

Complement component C3
Spontaneously activates and binds to nearby membranes
Host cells have control proteins on surface to prevent further complement activation/ bacteria do not- activate
Activates other C3s

Question 7

What are the effects of complement activation?

Answer 7

Membrane Attack Complex/ complement lysis
Anaphylatoxins
Opsonisation

Question 8

What is complement lysis?

Answer 8

Membrane Attack Complex (MAC) inserted into bacterial membrane
Barrel-like structure (C6-C9)- lesions
Water in, ions out- osmotic imbalance, swell and burst
Any cell marked

Question 9

What are anaphylatoxins?

Answer 9

Toxins that cause anaphylaxis
Leaky blood vessels/ increase vascular permeability- oedema= recruitment of immune cells, activation of mast cells (histamine)
Small bits of complement that disperse

Question 10

What is opsonisation?

Answer 10

Bind to surface of bacteria
Phagocytes have complement receptors which bind to membrane bound complement
Encourage phagocytosis and killing

Question 11

Name the innate immune cells that are phagocytes

Answer 11

Neutrophil, dendritic cell, macrophage

Question 12

Name the innate immune cells that are involved in allergic and anti parasite responses

Answer 12

Eosinophil, basophil, mast cell, Natural Killer cell (kills virally infected/ sick cells)

Question 13

Describe neutrophils

Answer 13

Killers, recruited rapidly to scene (30-80% WBC), very short lived as so toxic, chief constituent of pus

Question 14

Describe macrophages

Answer 14

Good killers if activated, reside in tissue, involved in tissue healing/ clearance of dead cells/ metabolism

Question 15

Describe dendritic cells

Answer 15

Poor at killing, rare, reside in tissue, initiates adaptive response- messenger to T cells

Question 16

What is extravasation?

Answer 16

Neutrophils transported from circulation to site of inflammation

Question 17

Describe the process of extravasation

Answer 17

Endothelium of blood vessels altered by inflammatory cytokines
neutrophils roll along endothelium, firmly adheres, exits between endothelial cells (diapedesis)
Follows chemokine gradient to site of inflammation

Question 18

Describe the process of phagocytosis

Answer 18

Phagocyte engulfs pathogen- phagosome formed
Lysosome fuse with phagosome- phagolysosome
Matures when more lysosomes fuse
Nitric oxide, oxygen radicals, proteases
Neutrophils make HOCl- bleach

Question 19

How are macrophages activated?

Answer 19

Danger signalling/ cytokines IFN gamma (interferon)

IFN gamma from NK cells, activated macrophages, helper T cells- makes more oxygen radicals

Question 20

What are NETs?

Answer 20

Neutrophil Extracellular Traps
Extrude DNA, traps pathogens= netosis (vs apoptosis and necrosis
Extracellular fungal infections

Question 21

Describe antigen presentation

Answer 21

Dendritic cells in periphery sense danger, take up antigens, mature/ high density of PRR
Upregulate different chemokine receptors
Migrate to lymphatics, drained into lymph node, present antigens to T cells

Question 22

Describe the structure of a lymph node

Answer 22

Afferent and efferent lymphatics
Blood supply- high endothelial venule
B cell follicle surrounded by T cell area in segments

Question 23

Why is antigen presentation so complicated?

Answer 23

So we don’t generate immune responses against harmless things (allergy/IBD) or your own tissues (autoimmunity)

Question 24

How are antigens recognised?

Answer 24

B cell receptor BcR recognises soluble antigen in native form
T cell receptor TcR have antigens presented to it on Major Histocompatibility Complex MHC molecules on another cell
Antigens hydrolysed by dendritic proteases, loaded onto MHC molecules and presented on cell surface

Question 25

How are T cells activated by signals?

Answer 25

MHC and TcR signal with peptide/ antigen presenting

Costimulation- dendritic cell upregulates B7, matures, signal

Question 26

What does anergy mean?

Answer 26

Unresponsive to future stimuli

Question 27

What is another signal that is used to coordinate T cell response?

Answer 27

Cytokines released from dendritic cells and other innate immune cells, best response depending on pathogen