Haematology and immunology: Pathology - General features of the immune system

Question 1

Define innate vs adaptive immunity

Answer 1

Innate: defense mechanisms present before infection and which have evolved specifically to recognise microbes
Adaptive: mechanisms stimulated by microbes, capable to recognising microbial and non-microbial substances

Question 2

Five components of innate immune system

Answer 2

1. Epithelial barrier (skin, mucosa)
2. Phagocytes (neutrophils, macrophages)
3. NK cells
4. Dendritic cells
5. Plama proteins (including complement)

Question 3

Two types of adaptive immunity and their functions

Answer 3

Cellular (T cell): intracellular microbes
Humoral (B cell): extracellular microbes and toxins

Question 4

Where are T cells generated?

Answer 4

Thymus

Question 5

How do T cells recognise specific Ag?

Answer 5

Via T cell receptors (TCRs)

Question 6

Main type of TCR. What does this receptor recognise?

Answer 6

AB (on 95% of T-cells)
Recognises Ag displayed on MHC by APCs

Question 7

On what cells is MHC I found?

Answer 7

All nucleated cells and platelets

Question 8

Which HLA encodes MHC I?

Answer 8

HLA-A, -B and -C

Question 9

On what cells is MHC II found?

Answer 9

Antigen-presenting cells (macrophages, dendritic cells, B cells)

Question 10

Which HLA encodes MHC II?

Answer 10

HLA-D

Question 11

Differentiate between the functions of CD4+ and CD8+ T-cells

Answer 11

CD4+: helper T cells, bind MHC I and secrete cytokines
CD8+: cytotoxic T cells, bind MHC II and induce cell death (also secrete cytokines)

Question 12

Cytokines secreted by TH1 cells

Answer 12

IFN-y

Question 13

Function of TH1 cells

Answer 13

Defends against intracellular microbes

Question 14

Role of TH1 cells in disease

Answer 14

Chronic inflammatory (AI) disease

Question 15

Cytokines secreted by TH2 cells

Answer 15

IL-4, IL-5, IL-13

Question 16

Function of TH2 cells

Answer 16

Defends against helminths

Question 17

Role of TH2 cells in disease

Answer 17

Allergy

Question 18

Cytokines secreted by TH17 cells

Answer 18

TGF-B, IL-1, IL-6, IL-23

Question 19

Function of TH17 cells

Answer 19

Defends against extracellular microbes and fungi

Question 20

Role of TH17 cells in disease

Answer 20

Role in chronic inflammatory (AI) disease

Question 21

Which cytokine induces proliferation of T cells into effector and memory T cells? What kind of signalling does this represent?

Answer 21

IL-2
Autocrine (also secreted by T cells)

Question 22

What % of the circulating peripheral lymphocyte populate do B cells constitute?

Answer 22

10-20%

Question 23

How do naive B cells recognise Ag?

Answer 23

Via B-cell Ag receptor complex with IgM and IgD

Question 24

What is the significance of CD21?

Answer 24

Receptor expressed by B cells which is also the EBV receptor

Question 25

Compare the contrast the roles of IgG, IgA and IgE

Answer 25

IgG: opsonising and complement-fixing, transported across placenta to provide newborn immunity
IgA: secreted from mucosal epithelia (respiratory, GI) to neutralise microbes
IgE: with eosinophils works to kill parasites (stimulated by TH2 cells)

Question 26

Three roles of macrophages in immunity

Answer 26

1. Antigen-presenting to T cells
2. Role in cell-mediated immunity (delayed hypersensitivity reaction)
3. Phagocytose microbes opsonised by IgG or C3b

Question 27

Two types of dendritic cells. Where are each found?

Answer 27

Interdigitating: found under epithelia and in interstitial tissue
Follicular: found in germinal centres of lymphoid follicles in spleen and lymph nodes

Question 28

What are Langerhans cells?

Answer 28

Dendritic cells found in the skin

Question 29

Function of interdigitating dendritic cells

Answer 29

Express receptors (e.g. mannose, TLRs) which capture and respond to microbes
Then recruited to T cell zones of lymphoid organs where they present Ag to CD4+ T cells via MHC II

Question 30

Function of follicular dendritic cells

Answer 30

Express Fc receptors for IgG and receptors for C3b
Trap antigen bound to antibody or complement

Question 31

What % of the circulating peripheral lymphocyte populate do NK cells constitute?

Answer 31

10-15%

Question 32

What is the role of NK cells?

Answer 32

First line defence against viruses and tumours

Question 33

What receptors are expressed by NK cells?

Answer 33

CD16
CD56

Question 34

How do NK cells preferentially kill virus-infected and tumour cells?

Answer 34

Cytotoxic action is inhibited by self class I MHC
Reduced expression of self class I MHC in virus-infected and tumour cells