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Undergrad Immunology > Primary and Secondary Lymphoid Organs > Flashcards

Primary and Secondary Lymphoid Organs Flashcards

1
Q

What are the primary lymphoid organs? (PLOs) What is their function?

A

Bone marrow and thymus.

Development of the immune cells.

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2
Q

What are the secondary lymphoid organs?

A

Where adaptive immune responses are initiated like…

Spleen, lymph nodes, tonsilds, adenoids, bronchus, Peyer’s patches, etc.

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3
Q

Describe how a T/B cell would get from the bone marrow to the secondary lymphoid organs? (SLOs)

A

T cell precursor would go from the bone marrow to the blood vessel to the thymus to differentiate then it would go back to the blood vessels to recirculate and head to the target area.
B cells leave the bone marrow and circulate in the blood until they get to their target.

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4
Q

Briefly describe the function of the bone marrow. What happens with age?

A

It is the seat of hematopoiesis. With age fat replaces 50% of the bone marrow.

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5
Q 
What is the function of...
Stromal cells?
Osteoblasts?
Endothelial cells?
Reticular cells?
Sympathetic neurons
A

Support HSCs
Bone formation and control HSCs
Line blood vessel and regulate HSC differentiation
Connect bone and vessels
Control the release of HSCs from bone marrow

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6
Q

Where do B lymphocytes develop?

Where do T cells develop?

A

Bone marrow.
In the Thymus

B=bone marrow
T=Thymus

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7
Q

Briefly describe the cytokines involved in B cell differentiation.

A

Chemokine CXCL12 is essential for generating pre-pro-B and pro-B cells.
IL-7 is essential for cell differentiation.
CXCL12 is alo involved in homing Ab producing plasma cells to the bone marrow where they take up long term residence.

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8
Q

Briefly describe the B cell generation and differentiation.

A

Bone marrow:

  1. Pro-B cells have a straight rod for an Ig.
  2. Pre-B cells have an immature Ig due to rearrangement of Ig. Selection process to eliminate self-reactive B cells.
  3. Immature B cell has mature Ig/BcR.

Periphery:

  1. T1Bcell
  2. T2Bcell
  3. Mature B cell
  4. Mature B cells can differentiate into Pre-plasma/Plasma B cells or memory B cells by Ag activation.
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9
Q

Discuss, in detail, T cell trafficking and maturity in the thymus.

A
  1. Circulating pre-T cells enter cortico medullary junction
  2. Double negative (DN) T cells migrate to capsule via CXCR4 and CCR7
  3. Migration to subcapsular zone via CCR9
  4. Double positive (DP) T cells interact with cTEC for +/- selection
  5. Positively selected DP T cells become CD4/CD8 SP cells and CCR7 brings them towards medulla expressing CCR7 ligands.
  6. Further SP selection T cells includes deletion of tissue-specific Ag reactive T cells and generation of Tregs.
  7. Mature SP T cells express S1P1 and are guided into circulation leaving as naive T cells. Tregs also leave here to maintain tolerance.
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10
Q

What is cTEC?

A

Cortical thymus epithelial cells. APCs that present self Ag.

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11
Q

Describe T cell selection types and how they are expressed?

A

A positive selection is kept and is expressed by an affinity for the MHC.
Negative selection is when the DP has too strong an affinity for the MHC and the T cell is killed.
Death by neglect is when there is no interaction with the MHC and the T cell dies.

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12
Q

What is AIRE? What is its function? Where is it located.

A

AIRE is the autoimmune regulator and is a key transcription factor in the thymus. It expresses tissue restricted antigens in the medullary thymus epithelial cells (mTEC) that show the T cells other parts of ‘self’ without leaving the thymus so it will not self-react.

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13
Q

Describe SLOs.

How are SLOs connected?

A

Areas where lymphocytes encounter Ag, become activated, undergo clonal expansion, and differentiate into effector cells.
Connected via blood/lymphatic circulatory systems.

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14
Q

What are the chemokines responsible for T cell homing to the lymph nodes? For T cell return to circulation?

A

CCR7

S1PR1

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15
Q

What are HEVs?

How do T cells reach in HEVs?

A

High endothelial venules.
Rolling - sensing
Activation - via CCR7 and CCL21
Arrest - ICAM1

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16
Q

Describe the organization of the lymph nodes.

A

Highly organized.
T/B cells separated: T cells in paracortex and B cells in follicles.
Cells migrate towards each other during activations that require B-T cell interactions

17
Q

Describe the lymph node…
Cortex.
Paracortex.
Medulla.

A

B cells, macrophages, and follicular DC arranged into follicles.
T cells and DCs
Egress for lymphocytes

18
Q

How do B cells respond to Ag in the lymph nodes?

A

Ag enters B cell zone via afferent lymph and is taken up by sub capsular sinus macrophages and follicular DCs. B cells can respond to free Ag or Ag complexes.

19
Q

How do T cells respond to Ag in the lymph nodes?

A

DCs bring Ag to the T cell zone and enter the HEV. DCs can present intact Ag to B cells and processed Ag to T cells. Micgrating DCs can then pass Ag to resident paracortex DCs

20
Q

How do B and T cells migrate int the paracortex of the lymph nodes?

A

B and T cells migrate in the paracortex via processes that arise from fibroblast reticular cells.

21
Q

Describe in detail the formation of germ centers in the lymph nodes.

A

Requires B-T cell interaction.

  1. Activated B cells engulf Ag and present to T cells in paracortex. Successful parring leads to B cell proliferation.
  2. B cells develop into plasma cells or can return to the follicle to establish a GC.
  3. BcRsomatic mutation allows for affinity maturation in the GC. This allows B cells to become much more Ag specific.
  4. Some B cells become memory which reside in the lymph node or recirculate and the plasma cells travel to medulla or bone marrow to secrete antibodies.
22
Q

What is the function of….
Memory B cells?
Plasma B cells?

A

Reside in lymph or recirculate

Travel to medulla or bone marrow to secrete Abs

23
Q

How long does it take to set up a GC?

How long do GCs remain active?

A

4-7 days

3 weeks

24
Q

What does MALT stand for?
What is MALT?
Where is MALT?

A

Mucosa associate lymphoid tissue
Lymphoid follicels found in mucosal membranes of digestive, respiratory, and UG tracts (type I) and epithelium (type II). They are pockets of DCs, B and T cells residing below M cells sampling incoming Ags.
Just under the epithelium

25
Q

What are microfold cells?

A

M cells are specialized to transport Ag across type I epithelium.

26
Q

What are the other kinds of MALT?

A 
BALT - bronchus
iBALT - inducible bronchus
NALT - nasal
GALT - gut
IEL - intraepithelial lymphocytes

Undergrad Immunology (16 decks)

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