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Physiology & Science: Defence & Immunity > Development of Immune Cells > Flashcards

Development of Immune Cells Flashcards

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1
Q

What is the principal function of lymphocytes?

A
  • Specific recognition of antigens
  • B lymphocytes: mediators of humoral immunity
  • T lymphocytes: mediators of cell-mediated immunity
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2
Q

Name 4 antigen-presenting cells

A
  • Dendritic cells
  • Macrophages
  • B cells
  • Follicular dendritic cells
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3
Q

What are the principal function(s) of antigen-presenting cells?

A
  • Capture of antigens for display to lymphocytes
  • Dendritic cells: initiation of T cell responses
  • Macrophages: effector phase of cell-mediated immunity
  • Follicular dendritic cells: display of antigens to B cells in humoral immune response
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4
Q

Name 3 effector cells and their role

A
  • T lymphocytes: activation of phagocytes, killing infected cells
  • Macrophages: phagocytosis + killing of microbes
  • Granulocytes: killing microbes

All result in elimination of antigens

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5
Q

Where are immune cells generated?

A

Bone marrow

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6
Q

What are the two specific lineages of immune cells?

A
  • Myeloid
  • Lymphoid
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7
Q

Which lineage are the following derived from?

  • neutrophils
  • macrophages
  • dendritic cells
  • mast cells
  • eosinophils
  • basophils
  • natural killer cells
  • B cells
  • T cells
A

All generated in the bone marrow, all are from myeloid lineage EXCEPT natural killer cells, B cells & T cells which come from the lymphoid lineage.

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8
Q

Dendritic cells are a type of antigen-presenting cell, they present the antigen bound to MHC. Where exactly do dendritic cells go to induce T lymphocyte activation?

A
  • Dendritic cells express membrane bound molecules + chemokine receptors
  • Chemokine receptors allow dendritic cells to migrate to lymph nodes
  • Here, there are naive T cells + B cells
  • Dendritic cell can present its antigens to the T cells here
  • Activation doesn’t happen in skin/gut/airways but happens in lymph nodes
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9
Q

What is the role of natural killer (NK) cells?

A
  • kill virus-infected cells
  • kill malignantly transformed cells (cancer cells)
  • express cytotoxic enzymes (lyse target cells)
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10
Q

Both subsets of lymphocytes have similar morphology but different functions. How so?

A
  • T cells - for cellular immunity
  • B cells - for humoral immunity, prod antibodies
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11
Q

Describe Th (helper) cells

A
  • Express CD4+
  • Activate macrophages
  • Help B cells to produce antibodies
  • Th1, Th2, Th17 cells
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12
Q

Describe CTL (cytotoxic) T Cells

A
  • Express CD8
  • Kill cells infected with microbes
  • Kill tumour cells
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13
Q

Describe Treg (regulatoy) cells

A
  • inhibit function of other T cells + immune cells
  • control of immune responses
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14
Q

What are the 3 subsets of B lymphocytes?

A
  • Follicular B cells (majority)
  • Marginal Zone B cells
  • B-1 cells

All produce different types of antibodies

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15
Q

Most immune cells are released into blood and are ready to work, such as granulocytes and monocytes. What about your resident APCs?

A
  • APCs - Dendritic cells & macrophages
  • These are present in all organs/tissues + especially at portals of entry (skin, airways, gut)
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16
Q

Where does lymphocyte maturation occur?

A
  • Immature T cells enter thymus where they continue maturation until stage of mature naïve T cells
  • Immature B cells continue maturation in bone marrow until stage of mature naïve B cells
17
Q

What are the central lymphoid organs and what are the peripheral lymphoid organs?

A
  • Central = bone marrow, thumus
  • Peripheral = lymph nodes, spleen, mucosal + cutaneous lymphoid tissue

The mature lymphocytes can travel from the central to peripheral lymphoid organs via blood + lymph.

18
Q

Immature lymphocytes are tested for the ability of what 2 things?

A
  • to recognise foreign antigens (ags) - useful
  • respond to self antigens - not useful + dangerous
19
Q

What is meant by the “checkpoints” in lymphocyte maturation?

A
  • Start with pro-B/T cell
  • Undergo proliferation
  • Pre-B/T cell expresses one chain of antigen receptor
  • Failure to express pre-antigen receptor -> cell death
  • Otherwise again proliferate
  • Some die
  • Surviving immature B/T cell expresses complete antigen receptor
    • weak antigen recognition -> positive selection -> MATURE B/T cell
    • strong antigen recognition -> negative selection (suggest self-antigen, dangerous)
20
Q

What are the stages of T cell maturation + selection?

A
21
Q

What are the 3 main outcomes of lymphocyte maturation?

A
22
Q

What is meant by “self / non-self discrimination”?

A

The immune cells are responsible for eliminating and controlling microbes and not to damage the host.

They should be able to discriminate between the host’s self antigens and the microbes’ foreign (non-self) antigens.

23
Q

In what manner are antigen receptors of T/B cells generated? What is a consequence of this?

A

Random generation occurs so…

  • self-reactive lymphocytes generated
  • self-antigens have access to immune cells

High likelihood of generating lymphocytes that have the potential to react against self-antigens (self-reactive lymphocytes)

24
Q

What is self tolerance?

A
  • AKA immunlogical tolerance
  • When self-reactive B/T cell have immunlogical unresponsiveness to self antigens -> self tolerance
25
Q

What will failure of self tolerance cause?

A
  • Autoimmunity
  • Self-reactive T/B cells attack own tissues/organs bc of self antigens
26
Q

Self-tolerance is achieved by central and peripheral mechanisms. What does it mean when central mechanisms result in central tolerance?

A

Induction of tolerance to self-Ags during lymphocyte development in central lymphoid organs

  • apoptosis
  • change in receptors/receptor editing (B cells only)
  • dvpt of Treg lymphocytes (CD4)
27
Q

What does it mean when peripheral mechanisms result in peripheral tolerance?

A

Tolerance to self-Ags is induced when mature lymphocytes respond to Ags in peripheral lymphoid organs or peripheral tissues

28
Q

Describe features of the central tolerance mechanism for T Cells

A
  • Scope -> eliminate cells recognising self Ags
  • Where? -> central lymphoid organs = thymus (thymus: only self Ags can be encountered)
  • Who? -> immature T lymphocytes (thymocytes)
  • How? -> clonal deletion (negative selection)

<5% of cells survive the developmental process! 95% will die anyway from no Ag recognition so death by neglect. Then the negatively selected ones apoptose. You’re left with formation of Treg cells and positively selected CD4/CD8 T cells (self tolerant!)

29
Q

How are CD4+ T cells and CD8+ T cells generated?

A
  • During positive selection, maturing T cells (thymocytes) that are double positive (co-express CD4 + 8) become either CD4+ T cells or CD8+ T cells (single-positive)
  • This choice depends on whether their randomly generated TCR recognises Ag presented by MHC II (->CD4) or presented by MHC I (->CD8)
30
Q

Some self-reactive T cells escape central tolerance, so go onto peripheral tolerance (back-up plan). Describe features of the peripheral tolerance mechanism of T Cells

A
  • Scope -> eliminate cells recognising self Ags (tissue specific self Ags expressed only in periphery)
  • Where? -> peripheral lymphoid organs (lymph nodes, spleen)
  • Who? -> mature T lymphocytes
  • How? -> multiple mechanisms + levels of control
31
Q

What are the 3 fates in peripheral tolerance?

A

So if a self-reactive T Cell makes it out of central tolerance into the periphery, there are 3 fates:

  • Anergy (inactivation)
  • Deletion (apoptosis)
  • Suppression (by Treg cell)
32
Q

Describe anergy induction in peripheral tolerance

A
  • recognition of self antigen
  • signalling block + engagement of inhibitory receptors (CTLA-4, PD-1)
  • -> unresponsive (anergic) T cell
  • anergic cells survive but do not respond to Ag
33
Q

What is meant by suppression by Treg?

A
  • Treg cells inhibit cell responses from naive T cell
  • Also inhibit other cells (B + NK cells)
  • Thymus-derived Treg or Treg generated in peripheral lymphoid organs suppress various immune cells
34
Q

What is meant by deletion in peripheral tolerance?

A

Recognition of self-Ag in absence of co-stimulation induces apoptosis of the responding mature T Cells

35
Q

Describe the mechanism of central tolerance in B cells

A
  • Scope -> eliminate B cells recognising self Ags
  • Where? -> central lymphoid organs = bone marrow
  • Who? -> immature B lymphocytes
  • How? -> deletion (die by apoptosis; negative selection)
    • -> change specificity (Ag receptor editing)
    • anergy
36
Q

In what stage of B cell maturation does receptor editing occur?

A
  • Receptor editing = light chain rearrangement
  • Occurs in immature B cells
37
Q

Describe the mechanism of peripheral tolerance in B cells

A
  • Scope -> eliminate/inactivate B cells recognising self Ags
  • Where? -> peripheral lymphoid organs (lymph nodes, spleen)
  • Who? -> mature B lymphocytes
  • How ->
    • deletion (die by apoptosis)
    • anergy
    • blockade of inhibitory receptors
    • suppression by Treg cells

Physiology & Science: Defence & Immunity (5 decks)

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