Innate immunity

Question 1

What are the 4 roles of the immune system?

Answer 1

1) Immunity to infection
2) Inflammatory process
3) Removal of senescent cells
4) Defence against neoplasia (cancer)

Question 2

Define antigen

Answer 2

Any substance capable of inducing a specific immune response

Question 3

Describe some differences between innate and adaptive immunity

Answer 3

I - primary line of defence
A - Secondary line of defence

I - Recognises certain threats (especially PAMPs)
A - Recognises all threats

I - No antigen presentation
A - Antigen presentation

I - No clonal selection
A - Clonal selection

I - No immunological memory
A - Immunological memory

Question 4

Name 4 physical barriers in the immune system

Answer 4

1) Skin
2) Mucus
3) Respiratory cilia
4) Commensal organisms

Question 5

Name 4 biochemical barriers in the immune system

Answer 5

1) Sebaceous secretions in skin
2) Lysozyme in tears
3) Spermine in sperm
4) Gastric acidity

Question 6

Define phagocytosis

Answer 6

Recognition and engulfing of microbes, which are then killed by the release of toxic chemicals into the enclosed vacuole.

Question 7

What are the 2 different cell types capable of phagocytosis?

Answer 7

1) Polymorphonuclear (PMN) leukocytes = neutrophils
- Innate system

2) Mononuclear phagocyte system (MPS) = monocytes and macrophages
- Adaptive system
- Antigen Presenting Cells (APCs)

Question 8

Describe the stages of phagocytosis

Answer 8

1) Chemotaxis and adherence of microbe to phagocyte
2) Ingestion of microbe by phagocyte
3) Formation of a phagocome
4) Fusion of the phagosome with a lysosome to form a phagolysosome
5) Digestion of ingested microbe by enzymes (oxidative burst)
6) Formation of residual body containing indigestible material
7) Discharge of waste material

Question 9

How do natural killer cells detect and kill infected/malignant cells?

Answer 9

Natural killer (NK) cells = lymphocytes that perform both direct &
antibody-dependant cell cytotoxicity (but process remains innate)

Normally all human cells express MHC Class I molecules on their surface, but these are lost in infected or malignant cells

NK cells detect this change (through lack of stimulation of inhibitor receptors), which leads to the NK cells becoming activated

Cytotoxicity comes from pore-forming molecules that are inserted into the target cell and cytotoxic chemicals are then pumped in

Question 10

Give 3 examples of PAMPs

Answer 10

1) Bacterial peptidoglycan
2) Lipopolysaccharide
3) Flagellin

Question 11

Give 4 examples of Acute Phase Proteins (APPs)

Answer 11

1) C-reactive protein (CRP)
2) Pro-calcitonin
3) Alkaline phosphatase
4) Ferritin

Question 12

Describe the stages in the alternative pathway of complement

Answer 12

1) C3 gets cleaved in the presence of certain microbial components
2) C3a → released → chemotaxis & local anaphylaxis
3) C3b → attaches to microbe → opsonisation & cleaves C5
4) C5a → released → chemotaxis & local anaphylaxis
5) C5b → attaches to microbe → activates C6, 7, 8 & 9
6) C5b, 6, 7, 8 & 9 → “membrane attack complex” → cell lysis

Question 13

Where are MHC Class I molecules found?

Answer 13

On all human cells except RBCs

Question 14

Where are MHC Class II molecules found?

Answer 14

Only on antigen-presenting cells eg. monocyte, macrophages etc.

Question 15

What do MHC Class I molecules present and to what?

Answer 15

Both classes present antigens from inside the host cell for inspection

Class I presents host, viral or neoplastic antigens to Tc lymphocytes
→ possible cytotoxic action by Tc lymphocytes

Question 16

What do MHC Class II molecules present and to what?

Answer 16

Both present antigens from inside the host cell for inspection

Class II presents ingested microbial antigens to Th lymphocytes
→ interaction with B lymphocytes to produce antibodies

Question 17

What is the interaction of MHC and T cell receptors called?

Answer 17

MHC Restriction