First Aid, Chapter 2 Cells Involved in Immune Responses, Lymphocytes

Question 1

What are the 3 types of lymphocytes?

Answer 1

B cells, T cells, and NK cells

Question 2

What are the general roles of helper T lymphocytes (CD4+ Th)? What are the markers?

Answer 2

Stimulate B-cell growth; secrete cytokines to activate macrophages; MHCII-restricted; markers CD3+/CD4+/CD8–.

Question 3

What are the major CD4+ families?

Answer 3

Th1, Th2, Th17, Th9, Tfh, Treg

Question 4

What are Th1 cells induced by? What do they produce? What are the transcription factors? What is the major function? What do they express? What diseases are they associated with?

Answer 4

Induced by: IL-12, IL-27, IL-18
Produce: IFNy, IL-2, TNF
Transcription factors: Tbet, STAT4, STAT1
Major function: Intracellular defense
Express: CXCR3, CCR5
Associated with: DM type 1, MS

Question 5

What are Th2 cells induced by? What do they produce? What are the transcription factors? What is the major function?

Answer 5

Induced by: IL-4, IL-25, IL-33, TSLP
Produce: IL-4, 5, 13; IL-6, 10, 21, 25, 31, 33
Transcription factors; GATA3, STAT6, STAT5
Major function: humoral immunity, antiparasitic, allergy

Question 6

What are Th17 cells induced by? What do they produce? What are the transcription factors? What is the major function? What do they express? What diseases are they associated with?

Answer 6

Induced by: IL-6, IL-1, 21, 23, TGFB
Produce: IL-17, IL-1, 6, 21, 22, TNFa, GM-CSF
Transcription factors: RORyT, STAT3
Major function: Extracellular defense; neutrophil recruitment; autoimmunit
Express: CCR6
Associated with: RA, IBD, MS, and psoriasis

Question 7

What are Treg cells induced by? What do they produce? What are the transcription factors? What is the major function? What are the 2 Treg subsets? What do they produce to suppress other T cells?

Answer 7

Induced by: TGFB and retinoic acid
Produce: IL-10, TGFB
Transcription factors; FOXP3, STAT5
Major function: Immunosuppression, prevents autoimmunity
Subsets: natural Tregs, Induced Tregs
Do not make IL-2, use cytotoxic T-lymphocyte antigen 4 (CTLA4) to suppress other T cells

Question 8

What are Th9 cells induced by? What do they produce? What is required for their differentiation?

Answer 8

Induced by: transforming growth factor beta (TGFB) and IL-4
Produce: IL-9 +/- IL-4
Require IRF4 and PU.1 for differentiation

Question 9

Where are Tfh (follicular helper T cells) located? What is their role? What is it mediated by? What does it produce?

Answer 9

• Located in the follicles of active germinal centers.
• Play a major role in helping B cells make antibodies.
• Mediated by transcription factor Bcl-6 (which causes downregulation of CCR7 and upregulation of CXCR5)
• Produce IL-21.

Question 10

Where are natural Tregs derived? What are they developed in response to? What do they express? What is their function?

Answer 10

Thymically derived and develop in response to thymically presented autologous antigens Constitutively express IL-2-Rα(CD25+) FOXP3+ Mediate self-tolerance

Question 11

Where are induced Tregs derived? What are they developed in response to? What do they express? What types of cells do they include?

Answer 11

Peripherally derived and develop in response to peripherally expressed self-antigens and external antigens Inducible IL-2–Rα(CD25) expression Include: Tr1(produce IL-10; involved in mechanism of immunotherapy), Th3 (produce TGFβ; in gut; important in IgA production)

Question 12

How do cytolytic T lymphocytes (CTLs and CD8) kill virally infectedcells and tumor cells? What do they express? What pathogenesis are they involved in? What do they use as a transcription factor? What markers do they have?

Answer 12

Kill viral-infected cells and tumor cells via perforin and granzyme; express IFN, TNF, and lymphotoxin; harder to activate than CD4s; involved in allograft rejection; use eomesodermin homologs (EOMES) as a transcription factor; MHCIrestricted; markers CD3+/CD8+/CD4–.

Question 13

Where to γδ T cells develop? Do they have a large diversity? What do they bind? What are the markers and chains required for signal transduction? Are they MHC restricted? What do they produce?

Answer 13

γδ T cells: These cells use γ and δ chains (instead of α and β chains); they develop in the thymus and have limited diversity; they can bind lipids and heat shock proteins; they are not associated with CD4 or CD8, but do require CD3 and the zeta chain for signal transduction; they do not recognize MHCassociated peptides and are not MHC-restricted; produce IFNy and TNF.

Question 14

What cells do NK cells kill? How do they know to kill them?

Answer 14

They kill viral-infected cells and tumor cells (due to these cells losing MHCI and gaining danger receptors).

Question 15

What cytokine is important for NK cell development?

Answer 15

IL-15

Question 16

What are markers on NK cells?

Answer 16

Markers include: CD16+ (FCRIII), CD56+ (NCAM), natural cytotoxicity receptors (NCRs), and killer inhibitory receptors (KIRs); do not express CD3.

Question 17

What is NK cell killing mediated via?

Answer 17

NK cell killing is mediated via perforin, granzymes, serglycine, and Fas.

Question 18

What do EBV-infected cells express to activate NK cells? What receptor does this bind on the NK cell?

Answer 18

EBV-infected cell expresses CD48 -> binds 2B4 receptor on NK cell

Question 19

What do stressed cells express that activate NK cells? What do they bind on NK cells?

Answer 19

Stressed cell expresses MICA/B, ULBP -> binds NKG2D on NK cell

Question 20

What do viral hemagglutinin bind to on NK cells? Does this activate or inhibit NK cells?

Answer 20

Viral hemagglutinin on target cell -> binds NKp44/46 on NK cell

Question 21

What does HLA-E bind to to activate NK cells? What does it bind to to inhibit NK cells?

Answer 21

Activation: HLA-E -> binds NKG2C on NK cell

Inhibition: HLA-E -> binds NKG2A/B

Question 22

What do IgG-bound target cells bind to on NK cells? Does this activate or inhibit them?

Answer 22

IgG-bound target cell -> binds FcyRIIIA on NK cell (ADCC)

Activates killing

Question 23

Which cytokines induce development of Th17 cells?

Answer 23

IL-6, TGFβ, IL-1, IL-21, and IL-23

Question 24

How are B and T cells segregrated in the lymph? WHat do they bind to cause this segregration?

Answer 24

Anatomic segregation of B and T cells:

• T-cell zone (parafollicular zone) -> T cell expresses CCR7, which binds CCL19/21 in the T cell/parafollicular zone (as the concentration/gradient of CCL19/21 is highest there).
• B-cell zone (follicles) -> B cell expresses CXCR5, which binds CXCL13 in the B-cell zone/follicles (as the concentration/gradient of CXCL13 is highest there).

Question 25

What cytokine is present in high levels during early maturation of B and T lymphocytes? What is deficiency of this cytokine associated with?

Answer 25

Maturation of B and T lymphocytes is characterized early on by high levels of IL7 (lack of this cytokine can lead to X-Linked severe combined immunodeficiency disease [SCID])

Question 26

What does positive selection insure during maturation of T cells?

Answer 26

That an individual's T cells can respond to peptides bound to his/her own MHC molecules.

Question 27

What sequences do VDJ recombinase recognize? Where are these sequences located?

Answer 27

It recognizes DNA sequences called recombination signal sequences (RSS); recombination occurs between two gene segments (immunoglobulin or TCR) only if one of the segments is flanked by one 12-nucleotide spacer and by one 23-nucleotide spacer -> 12/23 rule.

Question 28

In what cells is RAG1/RAG2 expressed? What does it do?

Answer 28

Expressed in immature lymphocytes (i.e., when antigen receptors are being assembled); cleaves double-stranded DNA between the coding segment and its recombination signal sequence.

Question 29

What does Ku do?

Answer 29

Binds DNA ends (hairpin in the case of the coding segment)

Question 30

What do DNA-PK (DNA-dependent protein kinase complex) and Artemis do?

Answer 30

Open DNA hairpin at a random site

Question 31

What does terminal deoxynucleotidyl transferase (TdT) do?

Answer 31

Adds nucleotides for junctional diversity (creates the greatest variability for diversity)

Question 32

What does endonuclease do?

Answer 32

Removes nucleotides for junctional diversity.

Question 33

What does DNA ligase IV:XRCC4 do?

Answer 33

Ligates DNA

Question 34

What markers are present in the pro B cell stage? What rearrangement occurs during this stage?

Answer 34

CD 19+, CD20+; Heavychain D-J then V-DJ rearrange ment

Question 35

What is produced in the pre B cell stage? What signalling and rearrangement occur?

Answer 35

Cytoplasmic µ chain produced here; signaling through pre-B–cell receptor and then light-chain V-J rearrangement.

Question 36

What occurs in the immature naive B cell stage?

Answer 36

Light-chain product (κ or λ) binds μ heavy chain to make IgM; receptor editing occurs

Question 37

What chains are expressed in the mature naive B cell? Via what process? What is expressed on the cell surface?

Answer 37

Express δ heavy chain (as well as μ) via alternative splicing so that IgM and IgD are expressed on the cell surface

Question 38

What occurs during the memory B cell and plasma cell stages? What type of mutations?

Answer 38

Memory cell: Isotype switch and somatic hypermutation occurs Plasma cell: Alternative splicing yields membrane and secreted Ig Flash

Question 39

At which stage does signaling through the pre-B–cell receptor occur?

Answer 39

Pre B Cell

Question 40

What does alternative splicing yield?

Answer 40

membrane versus secretory Ig

Question 41

What does differential splicing produce?

Answer 41

Differential splicing produces different immunoglobulin isotypes. IgD is the only Ig without a switch region; so, class switching will never apply to it

Question 42

What molecules, if absent, will not allow class switching? What disease occurs?

Answer 42

``` o AID, UNG, CD40, CD40L -> if lacking, cannot class switch -> Ig gets ‘stuck’ at IgM -> Hyper IgM phenotype ensues. ```

Question 43

What transcription factors are associated with commitment to the B cell?

Answer 43

Transcription Factors associated with commitment to the B cell include: PU.1, IKAROS, E2A, EBF, PAX5, and IRF8.

Question 44

What signals does B cell survival in the periphery depend on?

Answer 44

B-cell survival in the periphery depends on survival signals such as BLYSS, BAFF, and APRIL.

Question 45

What are the receptors on B cell for BLYSS, BAFF, and APRIL? Absence of which one is a risk factor for what disease?

Answer 45

BR3 and TACI (early on) and BCMA (later on). No TACI -> CVID risk factor

Question 46

What are the 3 types of mature B cells?

Answer 46

B1 cells, Marginal zone B cells, and B2 cells (conventional B cells or follicular B cells).

Question 47

What immune system are B1 cells categorized in? How much diversity is there? What cells are they analagous to? What percent of total B lymphocytes do they make up? What do they produce? What do they respond to? Where are they found? Are they T cell dependent?

Answer 47

Innate; limited diversity; analogous to γδ cells; make up 5–10% of total B lymphocytes; self-renewing; produce natural antibodies (low-affinity polyreactive immunoglobulins) that respond to microbes and lipids; found in peritoneal cavity and fetus; T-cell-independent.

Question 48

When are marginal zone B cells developed by? How quickly do they respond to antigens? Are they T cell dependent?

Answer 48

Developed by 2 years of age (which explains why infants have poor polysaccharide responses); first responders (especially to polysaccharide antigens); T–cell-independent.

Question 49

What cell types are included in B2 cells? What category of the immune system to they fall into? What do they respond to? Are they T cell dependent?

Answer 49

B2 cells (conventional B cells or follicular B cells): includes memory B cells and plasma cells; adaptive; respond to protein antigens; T–cell-dependent.

Question 50

Where are immature T cells located? What do they express? Where do they go when they undergo positive selection? Where do they go when they undergo negative selection?

Answer 50

When T cells are immature (DN; CD4–/CD8–), they are located in the subcapsular cortex. As they undergo positive selection, they move to the cortex. As they undergo negative selection, they move to the medulla.

Question 51

How do T cells leave lymphoid organs? What do they do next? What types of cells do they form?

Answer 51

T cells leave lymphoid organs by expressing sphingosine-1-phosphate (S1P) receptors. They undergo activation, expansion, and differentiation. Then memory or effector T cells form central memory T cells or effector memory T cells.

Question 52

What are the markers on central memory T cells and effector memory T cells.

Answer 52

Central memory T cells: CD45RA–, CD27+, CCR7+, CD62L+ (Lselectin). Effector memory T cells: CD45RA–, CD27–, CCR7–, CD62L– (Lselectin)

Question 53

Expression of what molecule commits T cells to develop?

Answer 53

Notch

Question 54

Do double negative T cells express the TCR? What are the stages of DN T cell? What happens at each stage, and what B cell stage is it analagous to?

Answer 54

Does not express T-cell receptor; stages: DN1, DN2 (β chain D-J then V-DJ rearranges; analogous to pro B cell), DN3 (signaling through pre-T–cell receptor; analogous to pre B cell), and DN4 (proliferation)

Question 55

What happens during the double positive stage of T cell maturation?

Answer 55

CD4+/CD8+; positive and negative selection occurs; α chain V-J rearranges

Question 56

What do single-positive thymocytes undergo? And what do they become?

Answer 56

Cells undergo selection to become CD4+ or CD8+

Question 57

Where does negative selection occur for T cells?

Answer 57

The medulla, which is also where the AIRE protein functions

Question 58

What are the two types of lymphocyte apoptosis?

Answer 58

Passive/intrinsic and active/extrinsic.

Question 59

What occurs in passive/intrinsic lymphocyte apoptosis? What pathways does it occur via? What is it mediated by?

Answer 59

Programmed death by neglect; mitochondrial pathways; mediated by caspase 9; bcl-2 and bcl-XL (antiapoptotic); bid/bim (proapoptotic).

Question 60

What are the steps of the active/extrinsic pathway of lymphocyte apoptosis? What is it mediated by?

Answer 60

Repeated lymphocyte activation causes increased Fas (CD95)/FasL(CD178) expression, which causes increased Fas-associated protein with Death Domain (FADD); mediated by caspase 8.

Question 61

What do both types of lymphocyte pathways converge on?

Answer 61

caspase 3

Question 62

What are the most common mutations seen in autoimmune lymphoproliferative syndrome (ALPS)? What does this result in?

Answer 62

Mutations in Fas(CD95) are the most common defect seen in autoimmune lymphoproliferative syndrome (ALPS), which results in defective lymphocyte apoptosis.