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Y1 Fwong MCD Immunology (A) > 2 Immune Cells And Organs > Flashcards

2 Immune Cells And Organs Flashcards

1
Q

Q: What is the process of lymphocyte production called?

A

A: LYMPHOPOIESIS

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2
Q

Q: What are lymphoid organs? What are they the site of?

A

A: Tissue in which lymphocytes interact with non-lymphoid cells.

Sites of initiation and maturation of adaptive immune response

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3
Q

Q: What are the primary lymphoid organs where T and B lymphocytes develop?

A

A: Thymus - T cell maturation

Bone Marrow - B cell maturation

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4
Q

Q: 3 secondary lymphoid organs.

A

A: Lymph nodes
Spleen (white pulp)
Mucosa-Associated Lymphoid Tissue (MALT)

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5
Q

Q: What are the precursors for B and T cells?

A

A: The precursors of both B and T cells come from haematopoietic stem cells in the bone marrow

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6
Q

Q: Are defects in primary and secondary lymphoid organs dangerous? What can treat them?

A

A: A defect in the primary lymphoid organs is very serious because you won’t produce your own lymphocytes. This can only be treated with stem cell transplant.

We can manage without some of our secondary lymphoid organs

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7
Q

Q: Anatomically, where is the thymus?

A

A: below the thyroid gland

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8
Q

Q: What does the microscopic analysis of a stained section of thymus show?

A

A: shows lobules within the lobes which are packed with lymphocytes

Medulla (middle) - NOT very stained
Cortex (periphery) - VERY stained

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9
Q

Q: What is the thymus structure?

A

A: bi lobed

lobules within the lobes which are packed with lymphocytes

There are septa dividing the lobe into lobules.

It has a capsule

In human’s you get whirls of fibroblasts called HASSALL’S CORPUSCLES

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10
Q

Q: What are Hassall’s corpuscles?

A

A: where regulatory T lymphocytes develop.

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11
Q

Q: What is the role of regulatory T lymphocytes?

A

A: important role in helping regulate our immune responses.

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12
Q

Q: How does the thymus appearance change after stimulation by an antigen (infection)?

A

A: no obvious changes

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13
Q

Q: How does thymic output change with age? What happens?

A

A: reduced output of new T cells

The total number stays the same

LESS DIVERSE repertoire of T cells

More memory cells

They become OLIGOCLONAL - less diverse

more fatty tissue in the thymus - size of the thymus DECREASES

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14
Q

Q: What is the site of haematopoiesis? How does this differ between a foetus and adults?

A

A: bone marrow

Foetus - All bones + liver and spleen

Adults - mainly the ends of the long bones where you find most of the marrow - the marrow becomes less cellular compared to young age and is replaced with with more fat droplets

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15
Q

Q: What does red and yellow marrow produce?

A

A: RED MARROW - blood cells

YELLOW MARROW - fat

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16
Q

Q: Where are lymphocyte precursors made?

A

A: haematopoietic tissue (bone marrow)

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17
Q

Q: What happens to T cells in the thymus?

A

A: T-cells are ‘educated’ - learn how to recognise cells presenting the antigen in the thymus

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18
Q

Q: How do lymphocytes and APCs recirculate?

A

A: Lymphocytes and antigen-presenting cells recirculate through lymphatic vessels: FROM tissues VIA lymph nodes and the spleen INTO the blood

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19
Q

Q: What does the lymphatic system allow?

A

A: Allows all fluid to be drained through the lymph nodes where it is filtered to identify any pathogens before it goes back into the blood.

Allows you to find out whether there is an infection in the body and where the infection is.

20
Q

Q: What is the structure of a lymph node?

A

A: Blood supply-
Afferent - IN
Efferent - OUT

B cell areas tend to be on the outside- aggregate into FOLLICLES

21
Q

Q: How does the structure of a lymph change upon infection?

A

A: PROLIFERATION of B lymphocytes - GERMINAL CENTER forms

Germinal Center - lymphocytes are rapidly proliferating to produce antibodies against the pathogen which caused the infection.

This makes your lymph nodes swell

22
Q

Q: How do lymphocytes enter the lymph nodes?

A

A: come in the circulation and leave via high endothelial venules and enter the lymph nodes.

They are directed by CHEMOKINE gradients via chemokinesis to their correct position.

23
Q

Q: How is an immune response triggered in a lymph node?

A

A: Dendritic cells migrate through the lymph and into the lymph nodes where it presents antigens to recirculating lymphocytes to trigger an immune response

24
Q

Q: What is the role of the spleen?

A

A: Filter for antigens IN THE BLOOD

25
Q

Q: What is the structure of the spleen?

A

A: White pulp immediately surrounds the blood vessels in the spleen

WHITE PULP - where the lymphocytes are

RED PULP - the rest of the spleen is red because this is the site of turnover of red blood cells

Splenic Artery brings the blood in and is surrounded by lymphocytes.

The area absolutely adjacent to the arteries is the periarterial lymphatic sheath (PALS) - mainly a T cell area

Adjacent to PALS is the B cell area.

26
Q

Q: How does the structure of the spleen change upon infection?

A

A: If there is an ongoing immune response you can get germinal centers in the spleen.

27
Q

Q: What are people without spleens more susceptible to?

A

A: INFECTIONS WITH ENCAPSULATED BACTERIA- Encapsulated = encapsulated with polysaccharide

28
Q

Q: What is MALT? Where is it found? 2 examples.

A

A: mucosal associated lymphoid tissue = aggregates of lymphoid tissue which do not have a tough outer capsule

lamina propria and sub-mucosal areas of the gastrointenstinal, respiratory and genitp-urinary tracts

tonsils and appendix and peyers patches

29
Q

Q: What is the first line of defence? Describe it.

A

A: epithelium

Mucosae + Skin = physical barrier

Large surface area + in many places, single layer of cells -> heavily defended by the immune system

30
Q

Q: What structures are near likely sites of infection?

A

A: some lymphoid tissue

MALT (mucosa-associated lymphoid tissue) and the cutaneous immune system are at these places

31
Q

Q: What is an example of gut associated lymphoid tissue?

A

A: PEYER’S PATCH - large aggregates of lymphocytes

32
Q

Q: How is the peyer’s patch organised?

A

A: Organised into B and T cell areas

Follicles can be seen here

Villi contain draining lymph vessels

There are lots of intraepithelial lymphocytes

include M cells

33
Q

Q: What do M cells do?

A

A: M Cells (microfold) - samples antigens from the gut and deliver antigens to the lymphocytes in the Peyer’s patch

34
Q

Q: How does the structure of the peyer’s patch change upon infection?

A

A: Contain germinal centers during immune responses

Predominantly B lymphocytes found here

35
Q

Q: Which cells are present in the cutaneous immune system? (7)

A

A: LANGERHANS CELLS - dendritic cells of the skin and mucosa -> Capture antigens in their local environment // Migrate via lymphatic vessels to draining lymph nodes

Lymphocytes

Keratinocytes- detect damage in skin and secrete signalling molecules to communicate this knowledge of damage

Dermis - you get tissue-resident macrophages

T lymphocytes circulate and can migrate to the skin if necessary

There is a dense network of immune cells in the skin (mainly langerhans cells and intraepidermal lymphocytes)

36
Q

Q: Why is a mechanism for recirculation of lymphocytes required?

A

A: Problem: There are large numbers of T cells and B cells with different specificities
There is a very small amount of antigen
There is need for a mechanism allowing the correct lymphocyte to come into contact with the antigen.

37
Q

Q: Describe the extravasation of naïve T lymphocytes into lymph nodes.

A

A:

38
Q

Q: Describe the mechanism that allows circulating lymphocytes to know when they have reached the HEV. Why is this important?

A

A: good as they need to know when it is time for them to leave the circulation and enter the tissue

High Endothelial Venules (HEV) - a specialised endothelium with a number of molecules involved in arresting the lymphocyte

  1. Rolling
  2. L selectin from the lymphocyte binds to CD34. Weak bond

There are special chemokines that are bound to the HEV - let lymphocyte know that they’ve reached the right place to enter the tissue.

  1. binding of lymphocyte to chemokine on HEV

surface receptor on the lymphocytes: Integrin: They have a low affinity and a high affinity binding form.

  1. binding of chemokine leads to activation of integrin in that it becomes its high affinity binding form (activation of the integrin to the high affinity binding form which leads to tight binding and immobilisation of the lymphocyte)
  2. Integrin can then bind to its ligand - ICAM-1 (Intracellular adhesion molecule 1) = adhesion
  3. The lymphocyte then becomes immobilised and can move into the tissue = transendothelial migration
39
Q

Q: Explain the use of CD (Cluster of Differentiation) markers for discrimination between lymphocytes.

A

A: All lymphocytes look the same under a microscope - large nucleus + small cytoplasm

Can be divided into B and T lymphocytes if we know where they’ve come from but they cannot be distinguished under the microscope.

EXPERIMENT: when people learnt to make monoclonal antibodies, they made monoclonal antibodies against the cell surface proteins of lymphocytes -> found that one particular cluster recognises one particular receptor and a different cluster recognises a different receptor.

It’s clusters of antibodies recognising cell surface proteins.

40
Q

Q: Describe T cell receptors’s associated co receptors

A

A: ALL EXPRESS CD3 - an integral part of the antigen specific receptor

There are two groups of TCR:
alpha beta - 90% in blood
gamma delta - 10% in blood

Out of alpha beta TCR:
CD4 - 2/3
CD8 - 1/3

41
Q

Q: What are the 2 T cell subsets? Examples. What does each subset do?

A

A: CD4+ = T Helper Cells, Regulatory T Cells - these secrete cytokines

CD8+ = Cytotoxic T Cells - lyse infected cells, secrete cytokines

42
Q

Q: What type of antigen do T cells recognise? How?

A

A: Only recognise PROCESSED ANTIGENS

Recognised by the TCR

Antigens must be presented by an Antigen-Presenting Cell on their cell surface by an Major Histocompatibility Complex (MHC) molecule

43
Q

Q: Describe B cell markers. What do they express? What can they present antigens to?

A

A: They don’t have any T cell markers

All Express CD19 and CD20

Express MHC Class II

Can present antigens to Helper T Cells

44
Q

Q: What type of antigen do B cells recognise?

A

A: Recognise INTACT ANTIGENS- DO NOT have to be processed and presented.

45
Q

Q: What is the BCR?

A

A: membrane anchored form of the antibody that they produce when activated.

The BCR has the same specificity as the antibody they produce when activated

46
Q

Q: What do APC do? How?

A

A: present processed antigens to T lymphocytes

The cells capture antigens from the outside - process the antigens - present peptides on the cell surface via MHC - triggers an immune response

47
Q

Q: What are the 3 types of APC? Location? What is a 4th type? What makes it different

A

A: Dendritic Cells- widely spread eg skin and mucosal tissue - presented at sites of likely infection

B Lymphocytes- lymphoid tissue

Macrophages (activated)- lymphoid tissue

Follicular dendritic cells- present to B cells- found in follicles in lymph nodes which trap antigens to help B cell responses in germinal centers

Y1 Fwong MCD Immunology (A) (9 decks)

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