immune response in peripheral lymphoid organs

Question 1

What happens to the B + T lympcytes after they mature and become immunocompetent in central Lymph organs

Answer 1

move to the peripheral or secondary lymphoid organs.
There, immune response is mounted and
carried out.

Question 2

what is antigen dependant differentiation

Answer 2

Lymphocytes meet antigen and are
activated by it. They proliferate to clones
and differentiate to effector and memory
cells.

Question 3

examples of peripheral lymphoid organs

Answer 3

lymph nodes, spleen, + mucosa-
associated lymphoid tissue (MALT).

Question 4

what do lymph nodes do + why they swell with infection

Answer 4

Antigens penetrating tissues (esp.
after injury) will be drained by lymph and brought
to the nearest lymph node to be dealt with.

Question 5

Structure of lymph node

Answer 5

covered in capsule of conn tissue

• cortex - mostly a B-cell area. It contains cell
  aggregates called follicles.
• paracortex - a T-cell area. There, T
  lymphocytes proliferate in cellular immune
  response.
• medulla - rich in antibody-secreting plasma
  cells.

Question 6

what are the follicles called if they are engaged in immune response and when they engaged in humoral response

Answer 6

1. primary (small and dense)

2.secondary (enlarges + middle
forms area called germinal center. This is site of proliferation + antigen-dependent differentiation of B lymphocytes.)

Question 7

What are HEV in lymph nodes

Answer 7

High Endothelial Venules

specialized blood vessels that deliver naïve lymphocytes from the bloodstream into the lymph nodes, where lymphocytes become matured by antigen-presenting cells
(e.g., dendritic cells).

Question 8

how do lymphocytes exit into blood

Answer 8

through efferent lymph vessels and into thoracic duct

Question 9

Steps of B cell differentiation in follicle

Answer 9

1. Antigen recognition at
   the periphery of follicle.
2. Stimulation by Тh (at the periphery).
3. If B cells stay at PERIPHERY, they do not
   undergo class switch and
   hypermutations; differentiated into SHORT- lived plasms cells.

4 B clells that enter GERMINATIVE CENTER of follicle undergoes class switch + somatic hypermutations. differentiated into LONG lived plasma + memory cells

Question 10

what does spleen do

Answer 10

reacts against blood borne antigens

Question 11

structure of the spleen

Answer 11

RED pulp - formed by cords + vascular sinuses. function = blood storage

WHITE pulp - is lymphoid organ. concentrated around arterioles

Question 12

page 9 for image of spleen. what is the periarteriolar. what is marginal zone

Answer 12

1. lymphoid tissue closest to the arteriole (t cell area)
2. peripheral white pulp bodering red (B cell area)

Question 13

What does Musosa assoc lymphoid tissue (MALT) do

Answer 13

reacts against antigens encountered at mucosal surfaces of respiratory, gastro-intestinal and genito-urinary tract.

Question 14

why is MALT also called non encapsulated lymphoid tissue. examle organs

Answer 14

its organs lack conn tissue capsules

tonsils, adenoids, peyers patches + appendix

Question 15

what kind of Ig does mucosa assoc humoral immunity rely on comapered to humoral immune response

Answer 15

IgA
humoral response = IgG

Question 16

what are MALT subcompartments

Answer 16

nasopharynx-associated lymphoid tissue,
bronchus-associated lymphoid tissue
gut-associated lymphoid tissue
genital tract-associated lymphoid tissue.

Question 17

does immune response occur in mammary glands

Answer 17

NO
but IgA antibodies are secreted to combat antigens in nasopharynx + gut

Question 18

Phases in immune response

Answer 18

1. Antigen presentation + recognition.
2. Lymphocyte activation.
3. Lymphocyte proliferation (clonal expansion) and antigen-specific differentiation.
4. Antigen elimination (effector phase).
5. Contraction of the immune response.
6. Memory.

Question 19

what a is the effector phase

Answer 19

• elimination of antigen mediated by specific antibodies
  and T cells. carried out i peripheral lymph organs

-

Question 20

how are effectors made

Answer 20

interction btw T + B lymphocytes and antigen presenting cells

• they interact by contact dependant and parcrine signalling (cytokines)

Question 21

what are t lymphocytes that haven’t participated in immune response called

Answer 21

naive , virgin, unprimed. in resting state

Question 22

how is a naive t cell activated

Answer 22

TCR needs to be engaged
co stimulatory signal needed ( delivered by membrane protein B7)

Question 23

what do dendritic cells express and where they found

Answer 23

MHC both classes+ B7

found under skin + mucosa (pathogens invade here)
in skin they called Langerhans cells)

Question 24

how does the dentritic cells activate t cells

Answer 24

After phagocytosing a particle, the dendritic cell migrates to nearest lymphoid organ to present its digested antigens.
There, it activates T cells, even if they are naïve.

Question 25

requiments for t helper cell activation

Answer 25

contact with MHCII + peptide and B7

Question 26

how are T killers activated

Answer 26

antigen presentation of MHC I + B7 AND TH1 helper recognizing same antigen

• T killers and T helpers specific for the same antigen stay close but cant recognise eachother
• they meet on the surface of antigen-presenting cell.
• The activation signal from the T helper is a cytokine, most likely interleukin 2

Question 27

How do dendritic cells present peptides both by MHC-I and MHC-II (antigen cross presentation)

Answer 27

After phagocytosis in dendritic
cell, pathogen is processed
in lysosomes + presented by
MHC-II to be detected by T helper.

Some protein molecules of the same pathogen can be
transferred to proteasomes;
these will be presented by MHC-I
to be detected by Tc.

This allows DC to contact both
Th and Tc and to keep them
close to each other.

Question 28

what else can antigen cross presentation allow dendtritic cells do

Answer 28

present viral antigens without being
infected by the virus.

Question 29

Once activated, T cells start to divide, forming
clones. what happens after this

Answer 29

proliferation by interlukin 2.
they become effector cells

when activated t cell recognises antigen with appropriate MHC, its triggered to act

Question 30

Is there a need for co simulatory signals for activated t cells.

Answer 30

No doesnt need B7 or interleukin 1 to kill

Question 31

so how does activated TC kill

Answer 31

they activate T killers + macrophages, and activated Th2 cells activate B cells.
Activated T killers and Th1 helpers do not stay only
in lymphoid organs but disseminate to other organs
by circulation.

Question 32

B cells only hv IgM receptors (as from bone M) for immune response they need IgD too. where do they get

Answer 32

obtain it from the same genes by alternative RNA processing and coexpress IgM and IgD.

Question 33

activation of B cells

Answer 33

1. do not need antigen presentation as T cells do. (can present antigen alone so acts like Ag presenting cell)
2. Thymus independent antigens causes B cells recognising them to proliferate and differentiate to secrete IgM antibodies

Question 34

what is specific abt germline centre B cells

Answer 34

high affinity, class switched antibodies
requires somatic hypermutation to dvlp

they origin of best memory B cells

Question 35

whats specific abt short lived antibodies

Answer 35

quickly forms in secondary lymph organs but apoptosis few days after antibody secretion.

some survive and become part of long term humoral immunity

Question 36

Most antigens are T-dependent and cannot
activate naïve B cells by themselves. They
need a T helper of Th2 type.
how do these recognise eachtoher

Answer 36

1. B cells internalize antigen bound to their
   receptors, process it + present it with class
   II MHC.
2. allows B cells to be recognised by T helpers specific for same antigen
3. T helper induces B cell to proliferate a + differentiate by cytokines

Question 37

Unlike IgD whch uses alternative splicing, how can B cell produce IGg, IgA, Igd?

Answer 37

site specific recombinsation

similar to VDJ