T cells: Development, Activation, and Immunity

Question 1

T-cell development:

Answer 1

T cells develop in the thymus from hematopoietic stem cells, undergoing positive and negative selection to become functional.

Question 2

Thymus selection process:

Answer 2

T cells undergo positive selection (survival if they can bind MHC molecules) and negative selection (elimination if they bind self-antigens too strongly).

Question 3

Positive selection:

Answer 3

T cells that can recognize self-MHC molecules on thymic epithelial cells are selected for survival.

Question 4

Negative selection:

Answer 4

T cells that bind self-antigens with high affinity are eliminated to prevent autoimmunity.

Question 5

T-cell receptor (TCR):

Answer 5

A receptor on T cells that recognizes specific antigens presented by MHC molecules on other cells.

Question 6

CD4+ T cells:

Answer 6

Helper T cells that recognize antigens presented on MHC Class II molecules and assist other immune cells.

Question 7

CD8+ T cells:

Answer 7

Cytotoxic T cells that recognize antigens presented on MHC Class I molecules and kill infected or cancerous cells.

Question 8

Naïve T cells:

Answer 8

Mature T cells that have not yet encountered their specific antigen.

Question 9

T-cell activation:

Answer 9

Occurs when a T cell’s TCR binds an antigen-MHC complex on an APC, followed by co-stimulatory signals for full activation.

Question 10

Co-stimulation:

Answer 10

Additional signals required for T-cell activation, often provided by B7-CD28 interaction between APCs and T cells.

Question 11

Effector T cells:

Answer 11

Activated T cells that carry out immune functions, including cytotoxic killing or cytokine secretion.

Question 12

Memory T cells:

Answer 12

Long-lived T cells that provide rapid protection upon re-exposure to the same antigen.

Question 13

Clonal expansion:

Answer 13

The proliferation of activated T cells to produce many copies of themselves to fight the pathogen.

Question 14

Helper T cell functions:

Answer 14

Secrete cytokines that activate B cells, cytotoxic T cells, and other immune cells, coordinating the immune response.

Question 15

Cytotoxic T cell functions:

Answer 15

Kill infected or cancerous cells by inducing apoptosis through mechanisms like perforin and granzymes.

Question 16

Treg (regulatory T cells):

Answer 16

Suppress immune responses to maintain self-tolerance and prevent autoimmunity.

Question 17

T-cell immune response:

Answer 17

T cells help mediate the immune response by recognizing and responding to infected cells, cancer cells, and foreign antigens.

Question 18

Activation of CD8+ T cells:

Answer 18

Requires antigen presentation on MHC Class I molecules and co-stimulatory signals, resulting in cytotoxic activity.

Question 19

Activation of CD4+ T cells:

Answer 19

Requires antigen presentation on MHC Class II molecules and co-stimulatory signals, leading to helper functions.

Question 20

Th1 cells:

Answer 20

A subset of CD4+ T cells that help fight intracellular pathogens, such as viruses, by activating macrophages and cytotoxic T cells.

Question 21

Th2 cells:

Answer 21

A subset of CD4+ T cells that help fight extracellular pathogens by promoting B cell activation and antibody production.

Question 22

Th17 cells:

Answer 22

A subset of CD4+ T cells involved in inflammation and defense against fungal infections.

Question 23

Tfh cells (follicular helper T cells):

Answer 23

A subset of CD4+ T cells that assist in B cell activation and antibody production in lymphoid follicles.

Question 24

T-cell differentiation:

Answer 24

The process by which T cells specialize into different subsets (e.g., Th1, Th2, Th17, Treg) based on cytokine signals.

Question 25

Cross-presentation:

Answer 25

Dendritic cells can present exogenous antigens on MHC Class I molecules, activating CD8+ T cells.

Question 26

T-cell memory formation:

Answer 26

Some activated T cells differentiate into memory T cells, which persist long-term and provide faster responses on re-exposure.

Question 27

Immune synapse:

Answer 27

The interface between an antigen-presenting cell and a T cell where TCRs and co-receptors engage with MHC-antigen complexes.

Question 28

T-cell exhaustion:

Answer 28

A state of dysfunction in T cells after prolonged activation, often seen in chronic infections or cancer.

Question 29

MHC restriction:

Answer 29

T cells can only recognize antigens when they are presented by MHC molecules, a phenomenon called MHC restriction.

Question 30

T-cell tolerance:

Answer 30

The process by which T cells learn to distinguish between self and non-self to avoid autoimmune responses.

Question 31

T-cell apoptosis:

Answer 31

Programmed cell death of T cells that occurs after they have performed their function or if they are autoreactive.

Question 32

Immune surveillance by T cells:

Answer 32

T cells monitor tissues for abnormal cells (e.g., infected or cancerous) and respond to threats.

Question 33

Memory T cell function:

Answer 33

Memory T cells respond more rapidly and effectively to subsequent exposures to the same antigen.