Lecture 12. T Cells and Adaptive Immunity

Question 1

What can the adaptive immune system do?

Answer 1

Destroy/eliminate invading organisms and any toxins that they produce

Question 2

What can the adaptive immune response raise immune responses against?

Answer 2

Pathogens that have never been encountered before by the host organism

Question 3

What are adaptive responses highly specific to?

Answer 3

A particular pathogen and provide long-lasting protection

Question 4

What is the name of any substance capable of generating an adaptive immune response?

Answer 4

Antigen

Question 5

What is the process of immunisation?

Answer 5

1. An antigen, a harmless molecule (typically a foreign protein), is injected into a mouse in the form of a suspension containing adjuvant
2. Adjuvant activates innate immunity responses
3. The activated innate response also responds to the antigen in the vaccine
4. This innate immune response then trains the adaptive immune response

Question 6

Where do lymphocytes develop?

Answer 6

In central or primary lymphoid organs (bone marrow, thymus)

Question 7

Where do lymphocytes migrate to after being developed?

Answer 7

Peripheral or secondary lymphoid organs (skin, respiratory tract)

Question 8

How many lymphocytes are there in the human body?

Answer 8

2 x 10¹²

Question 9

What did the transfer of lymphocytes into irradiated rodents restore?

Answer 9

Adaptive immunity, establishing that lymphocytes were responsible for adaptive immune responses

Question 10

How are dendiritc cells activated and what do they do?

Answer 10

DC are activated by binding of pathogen to any of these receptors
Activated dendritic cells phagocytose and degrade invading microorganisms
DC then migrate and travel to a nearby lymphoid organ such as a lymph node, where they activate adaptive immune responses, training them to recognise the peptide fragments that are carried

Question 11

How and where do T cells develop?

Answer 11

Develop in thymus tissue from thymocytes derived from common lymphoid progenitor cells, which are themselves derived from a haemopoietic stem cell originating in the liver (foetuses) or bone marrow (adults)

Question 12

How do dendritic cells activate T cells?

Answer 12

1. DC present peptides to T cells in the lymphoid organ
2. T cell TCR (T cell receptors) recognises ‘self’ antigen: no action taken
3. T cell TCR recognises no antigen: no action taken
4. T cell TCR recognises ‘non-self’ antigen: activation, mitosis and clonal expansion of specific T cells

Question 13

Why do antigen presenting cells only present to T cells?

Answer 13

1. Co-stimulatory molecules on APC ‘dock’ with T-cell specific co-stimulatory molecules
2. Peptide is held in the groove of an APC presenting protein and is ‘scanned’ by the TCR
3. No recognition: no action. Cells undock or Recognition: T cell activated

Question 14

What are the three types of T cell?

Answer 14

Helper T cells
Regulatory (or suppressor) T cells
Cytotoxic T cells

Question 15

What is the role of helper T cells?

Answer 15

Activate macrophages, dendritic cells, B cells and maintain cytotoxic T cell activity by secreting a variety of cytokines

Question 16

What is the role of regulatory T cells?

Answer 16

Inhibit the function of helper T cells, cytotoxic T cells and dendritic cells

Question 17

What is the role of cytotoxic T cells?

Answer 17

Kill infected host cells by persuading them to commit suicide apoptotically

Question 18

What do the contact points between a cytotoxic T cell and the target cell form?

Answer 18

Immunological synapse

Question 19

What are the two strategies cytotoxic T cells use?

Answer 19

1. The TC cell secretes perforins which assemble and form a channel in the target cell wall. The T cell then secretes specific proteases which enter the target cell, and activate caspases, the effector proteins of apoptosis
2. The TC cell binds receptors on the target cell that send a signal that activates caspases, the effector proteins of apoptosis