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Yr 2 - Clinical Pathology > Immunology - Cells of the Immune System > Flashcards

Immunology - Cells of the Immune System Flashcards

1
Q

What part of the immune system do B cells form?

A

Adaptive

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2
Q

What do B cells arise from?

A

common lymphoid progenitor cells within the bone marrow

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3
Q

Where do B cells migrate for maturation?

A

Don’t migrate - remain in bone marrow

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4
Q

Two selection processes happen during B cell development.

What are these?

A
  1. Positive selection

2. Negative selection

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5
Q

What does positive B cell selection involve?

A

Ensures that only B cells with functional receptors develop further.

This occurs when the B cell receptor successfully binds its ligand, which induces survival signals.

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6
Q

What does negative B cell selection involve?

A

Testing if B cells respond to self-antigens in the bone marrow –> this results in receptor editing, anergy or apoptosis.

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7
Q

What is the purpose of B cell negative selection?

A

Promotes central tolerance and minimises the risk of autoimmune reactions

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8
Q

What is the first class of antibody to appear on developing B cells?

A

IgM

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9
Q

Once differentiated in the bone marrow, where do B cells migrate to?

A
  1. Lymphoid follicles in the spleen.

2. Areas where lymphoid activation and defence is likely to be triggered such as in the mucosal lining.

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10
Q

What are Peyer’s patches?

A

Peyer’s patches are small masses of lymphatic tissue found throughout the ileum region of the small intestine. They play an important role in immune surveillance of materials within your digestive system.

This is a type of mucosa-associated lymphoid tissue (MALT).

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11
Q

Other ‘MALTs’ also exist and are named according to their location or organisation.

What are 3 examples of these?

A
  1. Bronchial (BALT)
  2. Nasal (NALT)
  3. Organised-mucosa (O-MALT).
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12
Q

What is the major function of B cells?

A

Responsible for mediating the production of antigen-specific immunoglobulin (Ig) directed against invasive pathogens

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13
Q

How are B cells activated?

A

When their B cell receptor (BCR) binds to an antigen

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14
Q

In their inactivated state, what Ig do B cells express?

How does this change once activated?

A

In their inactivated state B cells express IgM/IgD.

Once activated they may express IgA, IgE, IgG or retain IgM expression.

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15
Q

B cells have two main types of immune responses: T-Independent and T-dependent.

Describe each

A

T-independent: B cells can respond directly to the antigen

T-dependent: B cells need assistance from T cells in order to respond

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16
Q

How do T cells assist B cells in an immune response?

A

Once a helper T cell has been activated by an antigen, it becomes capable of activating a B cell that has already encountered the same antigen.

These B cells then multiply into clones of immunoglobulin-secreting cells –> clonal expasion

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17
Q

Which protein is involved in T cell and B cell interaction?

A

CD40 ligand which appears on the surface of the activated helper T cells, and the CD40 protein on the B-cell surface.

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18
Q

How can T cells stimulate B cell activation?

A

CD40 ligand found on T helper cells interacts with CD40 on the B cells e.g. IL-4, IL-5, and IL-6

Cytokines secreted by T cells encourage: proliferation and isotype (Ig) switching

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19
Q

Once activated, B lymphocytes can differentiate into plasma cells. What are plasma cells?

A

Plasma cells are terminally differentiated cells of the B lymphocyte lineage –> able to secrete antibodies and are the cell responsible for antibody-mediated immunity.

Can produce large quantities of antibodies against specific antigens.

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20
Q

How do plasma B cells differ from memory B cells?

A

When memory B cells reencounter their specific antigen, they proliferate and differentiate into plasma cells –> produce specific antibodies

21
Q

What stimulates this differentiation of B cells into plasma cells?

A

Once stimulated by the appropriate antigen, Th cells secrete cytokines, which stimulate the differentiation of B cells into plasma cells (Ab-producing cells).

22
Q

What type of B cells are often seen in chronic inflammation?

A

Plasma cells

23
Q

What type of bacteria are T-independent B cells particularly important for dealing with?

Why?

A

Encapsulated bacteria

Encapsulated bacteria have a polysaccharide outer layer as opposed to a protein-based one, which allows them to evade T cells.

T-independent B cells can recognise these layers and produce antibodies without T cell help.

24
Q

What is XLA?

A

X-linked Agammaglobulinemia, also known as Bruton’s disease.

WHAT: Is a rare genetic disorder that affects the body’s ability to fight infection

PATHOGENESIS:

1) Defect in BTK gene found on X chromosome
2) Defect in Bruton’s Tyrosine Kinase( BTK)
3) BTK needed for B cell signalling and maturation; patients are unable to produce mature B lymphocytes.

CLINICAL FEATURES: They tend to have an absence of serum immunoglobulins post 6 months (after maternal IgG have been broken down).

25
Q

How do patients with XLA present? What are common causative pathogens of infections?

A

Infections that are severe, persistent, uncommon and recurrent.

Haemophilus influenzae, Streptococcus pneumoniae, and staphylococci are common causative pathogens.

26
Q

Treatment for XLA?

A

Immunoglobulin replacement therapy and patients may also require prophylactic antibiotics.

Patients with XLA should not receive live vaccines.

27
Q

What are the 3 broad roles of T cells?

A
  1. directly killing infected host cells
  2. activating other immune cells
  3. producing cytokines and regulating the immune response.
28
Q

Where do T cells originate?

A

from haematopoietic stem cells which are produced in the bone marrow.

29
Q

When do T cells (thymocytes) then migrate to for development?

A

thymus via the blood

30
Q

Describe positive selection process of thymocytes

A

Thymocytes in the thymus express both CD4 and CD8 co-receptors –> can bind both MHC I and II.

Antigens are then presented to thymocytes by both MHC I and II.

If they recognise any antigen they become positively selected and start to express EITHER CD4 or CD8. It is decided whether they become Th or Tc cells.

If cell recognised peptide presented by MHC I –> CD8+ (Tc)

If cell recognised peptide presented by MHC II –> CD4+ (Th)

31
Q

Describe negative selection of thymocytes

A

Surviving T lymphocytes continue to migrate through medulla and are now presented with self-antigens.

Thymocytes that have receptors to self-antigen molecules receive negative signals and are removed.

32
Q

After maturation, T cells leave the thymus and go where?

A

They will circulate through the peripheral lymphoid organs as naive T cells, ready to encounter a specific antigen and become activated.

33
Q

What are naive T cells?

A

Cells that have not yet encountered their specific antigen

34
Q

What are 2ary/peripheral lymphoid organs?

A

They include the lymph nodes, spleen, tonsils, and mucosal-associated lymphoid tissues in which immune responses are induced.

35
Q

APCs can present antigens to naive T cells via MHC molecules. What is effect on T cells of this?

A

If the T lymphocyte recognises a specific antigen, it will proliferate and differentiate into effector T lymphocytes of a particular type.

The cell either uses a co-receptor called CD8 or CD4 to bind to the MHC molecule.

Naïve T lymphocytes with CD8 –> become cytotoxic T cells

Naïve T lymphocytes with CD4 –> become T helper cells

36
Q

What is role of cytotoxic T cells (CD8+)?

A

Cytotoxic T lymphocytes kill their target cells primarily by releasing cytotoxic granules into the cell to be killed.

37
Q

What MHC class do CD8+ cytotoxic T cells recognise?

A

These cells recognise their specific antigen when presented by MHC Class I molecules that are present on the surface of all nucleated cells.

38
Q

What cells express MHC Class I?

A

on the surface of all nucleated cells

39
Q

T helper cells (Th) have a wider range of effector functions than CD8 T cells and can differentiate into many different subtypes.

What are these subtypes?

A

Th1, Th2, Th17 and regulatory T cells.

40
Q

What MHC class do CD4+ T helper cells recognise?

A

They become activated when they are presented with peptide antigens by MHC Class II molecules.

41
Q

What cells express MHC Class II?

A

ACPs

42
Q

What is role of Th cells?

A

A activating other immune cells, releasing cytokines, and helping B lymphocytes to produce antibodies.

43
Q

What are memory T lymphocytes?

A

Following an infection, antigen-specific, long-lived memory T lymphocytes are formed –> an quickly proliferate into large numbers of effector T lymphocyte upon re-exposure to the antigen and have a low threshold for activation.

They provide the immune system with memory against previously encountered antigens. Memory T lymphocytes may either be CD4+ or CD8+.

44
Q

T helper cells secrete cytokines. What do these do?

A

Activate B cells
Attract macrophages and other lymphocytes
Activate more T cells

45
Q

What is SCID?

A

Severe Combined Immune Deficiency

A group of primary immunodeficiencies with defects in both T and B cell numbers and/or function.

46
Q

What are SCID patients prone to?

A

recurrent infections, sepsis and failure to thrive.

47
Q

What is the treatment for SCID?

A

Bone marrow transplant

48
Q

What is the most common genetic defect that results in SCID?

A

X-linked

Yr 2 - Clinical Pathology (80 decks)

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