Lecture 9.2: Adaptive Immunity

Question 1

Adaptive Immunity

Answer 1

• Immunity established to adapt to infection
• Learnt by experience.
• Confers antigen-specific immunity
• Enhanced by second exposure
• Memory
• Ineffective without innate immunity

Question 2

Types of Adaptive Immunity (2)

Answer 2

Humoral
Cell Mediated

Question 3

Adaptive Immunity: Humoral and Cell-Mediated

Answer 3

• Mediated by T and B lymphocytes, NKT cells
• Provides defence against both intracellular and extracellular antigens

Question 4

Adaptive Immunity: Humoral

Answer 4

• Antibodies produced by B lymphocytes (circulation and mucosal fluids)

Question 5

Adaptive Immunity: Cell-Mediated

Answer 5

• Phagocytes are activated
• Cytotoxic T cells interact with pathogenic cells

Question 6

How do T and B cell specificities differ?

Answer 6

• T cells only recognise proteins
• B cells recognise proteins, carbohydrates, nucleic acids

Question 7

Natural Killer T Cells

Answer 7

• Recognise IgG, lipids, MHC class I, secrete cytokines (IFN, TNF, IL12)
• Kill tumour cells and virally infected cells
• Induce apoptosis by pumping proteases through target cell membrane
• Like DC cells, NKT cells determine the type of adaptive response

Question 8

What does CD stand for?

Answer 8

Cluster of Differentiation

Question 9

T-Cells: CD8+

Answer 9

Cytotoxic

Question 10

T-Cells: CD4+

Answer 10

Helper

Question 11

What does Antigen Recognition rely on?

Answer 11

It relies on presentation of antigens by cells of the innate immune system

Question 12

Antigen Recognition

Answer 12

• Antigen presenting cells (APCs) take up antigen (peptide fragment presented)
• Cells divide, form clones of cells that respond to antigen (clonal selection)

Question 13

Effector Cells and Negative Selection

Answer 13

Effector cells subject to negative selection (autoimmune disease) where cells expressing ‘self’ are destroyed

Question 14

How is antigen repertoire developed?

Answer 14

Repertoire develops without exposure to antigen through stem pcell differentiation

Repertoire present before encounter with antigen

Question 15

Naive T Cell

Answer 15

A T cell that has matured and been released by the thymus but has not yet encountered its corresponding antigen

Express antigen receptors

Do not eliminate antigen

Question 16

Effector Cell

Answer 16

Differentiated progeny of naive cells after antigen exposure

Cells produce molecules to eliminate antigen

Question 17

Memory T and B cells

Answer 17

Following antigen exposure, activated T and B cells persist as memory cells

Memory cells are close to sites of reinfection for rapidity of response

Question 18

Phases of the Adaptive Response

Answer 18

Antigen Recognition
Lymphocyte Activation: Clonal Expansion of T and B Cells
Antigen Elimination: Humoral and Cell Mediated
Contraction (Homeostasis): Apoptosis
Memory: Memory Cells Endure

Question 19

Where are Antigen Presenting Cells (APCs) found?

Answer 19

• Skin (SALT)
• Mucous membranes (GALT, NALT, BALT)
• Lymphoid organs (Lymph nodes, spleen)
• Blood circulation (plasmacytoid and myeloid dendritic cells)

Question 20

Phagocytosis

Answer 20

Captures whole microbe

Question 21

Macropinocytosis

Answer 21

Capture of soluble particles from pathogen

Question 22

What is a PRR

Answer 22

Pattern Recognition Receptors
Diversity in pathogen sensors (PRRs) is a feature of APCs

Question 23

What antigens to TCRs and BCRs bind to?

Answer 23

TCRs and BCRs bind antigens presented by MHC molecules

Question 24

What 2 signals are required to activate lymphocytes (for proliferation)?

Answer 24

• TCR
• Verification signal

Question 25

Lymphoid Tissue Activation

Answer 25

In lymphoid tissue naive CD4 or CD8 proliferate and differentiate

Question 26

Peripheral Tissue Activation

Answer 26

In peripheral tissue CD4 effectors activate macrophages and B cells, whilst CD8 cells kill infected ‘target cells’ and activate macrophages

Question 27

Delayed Type Hypersensitivity

Answer 27

Th1 and Th17 are involved in DTH reactions to antigens

Question 28

Helper T cells (CD4+)

Answer 28

• Activate other cells
• Macrophages containing microbes
• B cell class switching

Question 29

Cytotoxic T cells (CD8+)

Answer 29

• Kill cells expressing recognised abnormal antigens
• Normal cells containing viruses
• Mutated/Cancerous cells

Question 30

Effector Mechanisms T Cell Responses: Extracellular Microbes

Answer 30

Eosinophils: Killing of Parasites
B-Cells: Antibodies
Mast Cells: Local Inflammation Allergies (IgE)
Neutrophils: Phagocytosis which leads to autoimmunity

Question 31

Effector Mechanisms T Cell Responses: Intracellular Microbes

Answer 31

CD8+: Cytotoxic T Lymphocyte, release perforins granzymes
B-Cells (Isotype Switching): Antibodies (IgG2-3)
Macrophages: Phagocytic activities, Kill opsonized microbes, Autoimmunity, chronic inflammation

Question 32

Antibody Structure

Answer 32

Heavy Chains Inside
Light Chains Outside
Fab: Variable Region specific to antigens
Fc: Invariable region of antibody

Question 33

Importance of Fc Region on Antibody

Answer 33

Fc region of antibody attracts NK cells and phagocytes

Question 34

B-Cell Memory Development

Answer 34

After isotype switching, B cells continue maturation to improve specificity to antigen

High affinity, class switched B cells become memory cells

Migrate to sites of pathogen entry

Question 35

Contraction

Answer 35

• Elimination of microbes = loss of activation signals
• Treg cell signalling outweighs activation signals
• Reduction in response, apoptosis of phagocytes
• Surviving lymphocytes are memory cells

Question 36

T-Cell Memory

Answer 36

Multiple cell types in different locations with different groups of CD surface markers (lymph nodes, circulation, MALTs)

Pool of memory cells determined by future exposure

TCRs recognising conserved regions more likely to remain long term

Converted to effector cells on second encounter with antigen that binds receptor

Question 37

Characteristics of the Memory Response (6)

Answer 37

Faster
Stronger
Longer Duration
Higher Affinity
Isotype Switch Affinity Maturation
Use Th Cells