Lymphocytes

Question 1

Lymphocyte definition

Answer 1

A subtype of white blood cell

Question 2

four different types of lymphocyte

Answer 2

B cell, T cell, natural killer cell, small lymphocyte

Question 3

stages of development of lymphocytes

Answer 3

1. stem cells differentiate in bone marrow
2. all lymphocytes originate from a common lymphoid progenitor
3. B cells mature into B lymphocytes in the Peyer’s patches of the intestine
4. T cells migrate to and mature in a distinct organ called the thymus

Question 4

What are the Peyer’s patches?

Answer 4

Organised lymphoid follicles, found in the distal jejunum and ileum

Characterised by the follicle- associated epithelium

Question 5

Function of Peyer’s patches

Answer 5

trap foreign particles, surveil them and destroy them. Lymphocytes and antigens meet here ( and the lymph nodes), not the blood

Question 6

Structure of Peyer’s patches

Answer 6

covered in special follicle associated epithelium that contains special microfold cells- sample antigen directly from the lumen and deliver it to APS cells

APS cells located in a pocket structure on the basolateral side

Question 7

Development of T cells explained

Answer 7

1. originate from haematopoietic stem cells which reside in the bone marrow
2. HSC then differentiate into mutipotent progenitors- myeloid and lymphoid
3. lymphoid cells then differentiate into T, B or NK cells- called common lymphoid progenitors

Question 8

Secondary lymphoid organ definition

Answer 8

location for antigens to encounter lymphocytes. Region where the lymphocytes proliferate

Question 9

examples of secondary lymphoid organ

Answer 9

lymph nodes, spleen and Peyer’s patches

Question 10

How do all the lymphocytes connect the dispersed lymph tissue?

Answer 10

leave blood at special endothelium, only on certain venules within lymph nodes, tonsils and other lymphoid organs

Question 11

primary lymphoid organ definition

Answer 11

lymphatic regions where the lymphocytes mature- thymus and bone marrow

Question 12

Two main types of T cell

Answer 12

helper T cell and killer T cell

Question 13

What differs between them?

Answer 13

cytotoxic T cell have a CD8 antigen receptor, whereas helper T cells have a CD4 receptor

Question 14

Helper T cell function

Answer 14

Play a role in adaptive immunity

Release T cell cytokines that stimulate killer cells

Bind to antigens found on antigen presenting cells, Th cell then binds and lead to the release of cytokines

Question 15

Cytokines definition

Answer 15

small proteins that are important in cell signalling

Question 16

Cytotoxic T cell function

Answer 16

immune surveillance

patrols body for ‘missing self’ absence of cell surface ‘passport’ molecules

CD8 receptors bind to specific antigens

Kills cancer cells, cells that are infected by a pathogen or that are damaged in another way

Question 17

How do killer T cells induce destruction?

Answer 17

Release cytotoxins, such as perforin, granzymes and granulysin- target cell that causes a caspase cascade that leads to apoptosis

Question 18

What are MHC molecules?

Answer 18

surface proteins essential for the acquired immune system to recognise antigens

Question 19

MHC molecule functions

Answer 19

bind to antigens and present them on their surface for recognition

Question 20

Relationship between MHC, Th and Tc

Answer 20

As a lineage of leukocytes, lymphocytes reside in peripheral lymphoid tissues, including lymphoid follicles and lymph nodes, and include B cells, T cells, and natural killer cells (NK cells). B cells, which act specifically, secrete antibody molecules, but do not bind MHC. T cells, which act specifically, as well as NK cells, which act innately, interact with MHC. NK cells express Killer Ig-like receptors (KIRs) that bind to MHC I molecules and signal through ITIM (immunoreceptor tyrosine inhibition motif) recruitment and activation of protein tyrosine phosphatases. This means in contrast to CD8/TCR interaction that activates Tc lymphocytes, NK cells become deactivated when bound to MHC I. When MHC class I expression is low, as is typically the case with abnormal cell function during viral infection or tumourigenesis, NK cells lose the inhibitory KIR signal and trigger programmed cell death of the abnormal cell. NK cells thus help prevent progress of cancerous cells by contributing to tumor surveillance.

Question 21

B cell function

Answer 21

Humoral immunity component of the adaptive immune system- secrete antibodies

Can become antigen presenting cells and secrete cytokines

Question 22

What happens if an early B cell binds to a self antigen?

Answer 22

clonal deletion, receptor editing, anergy or ignorance

Question 23

What does this result in?

Answer 23

State of central tolerance- mature b cells don’t bind to self antigens in bone arrow

Question 24

Where do the B cells move after the bone marrow?

Answer 24

Migrate into the spleen, transition from T1 to T2 B cells

Question 25

Where do the B cells become activated?

Answer 25

secondary lymphoid organs- spleen and lymph nodes

Question 26

B cell functions

Answer 26

mature into antibody producing cells and plasma cells

Question 27

Plasma cell function

Answer 27

antibody secreting cell arising from B cell differentiation

Question 28

What are small lymphocytes?

Answer 28

quiescent (inactive), non dividing cells that re-circulate

Question 29

Process of recirculation

Answer 29

Move through tissues by migrating through post-capillary venules and via tissue fluid, lymphatics and lymph nodes back into the blood

Question 30

Small lymphocyte functions

Answer 30

monitor tissues for presence of antigens

Question 31

Lymphoblast definition

Answer 31

modified naive lymphocyte with altered cell morphology, that occurs when the lymphocyte is activated by an antigen from an APS cell.

Question 32

Structure of lymphoblast

Answer 32

increased volume due to nucleus and cytoplasm growth, as well as new mRNA and protein synthesis

Question 33

What happens after the lymphoblast is activated?

Answer 33

begins to slowly divide- producing roughly 1000 clones and then develops into effector cells

Question 34

Another important type of B cell

Answer 34

memory B cells

Question 35

Memory B cell function

Answer 35

remain in blood, able to better respond upon secondary infection

Question 36

How memory cells are formed

Answer 36

1. B cells proliferate and mutate the region coding for their surface antibodies
2. After gaining a set of mutations, the germinal centre B cells are subjected to a round of selection by Tfh cells.
3. The mutated B cells have a higher affinity surface of antibodies that then better recognise antigens
4. these are retained in the germinal centre to re enter another round of replication

Question 37

Germinal center definition

Answer 37

sites within secondary lymphoid organs where mature B cells proliferate, differentiate and mutate their antibody genes

Question 38

Somatic hypermutation definition

Answer 38

Cellular mechanism by which the immune system adapts to the new foreign elements

Leads to a high rate or somatic mutation that eventually lead to the B cell’s enhanced ability to recognise and bind a specific antigen

Question 39

Immunoglobin definition

Answer 39

antibodies