Lecture 36 Flashcards

1
Q

What does tolerance ensure

A

That the immune system avoids destroying host tissue
Helps keep self-reactive recognition molecules/cells (BCRs and TCRs) from circulating in the blood stream

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2
Q

Where do T cells develop

A

Initially in bone marrow (early stages) but then migrate to thymus (reach maturity)

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3
Q

Name of developing T cells

A

Thymocytes

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4
Q

Parts of the Thymus

A

Cortex–>top/superficial
Medulla–>bottom/deep

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5
Q

Which cells are in the cortex of the thymus

A

Cortical epithelial cells and thymocytes

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6
Q

Which cells are in the medulla of the Thymus

A

Medullary epithelial cells, macrophages, and conventional dendritic cells

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7
Q

How do T cell precursors enter the thymus from bone marrow

A

As double negative (DN) cells
Don’t express CD4 OR CD8

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8
Q

Pathway of receptor expression during T cell development

A

Double negative (DN), no expression of CD4 OR CD8–>Double positive (DP), expresses BOTH CD4 AND CD8–> Single positive (SP), expresses EITHER CD4 OR CD8

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9
Q

Outcome of Positive selection in T cells

A

MHC restriction
Selecting thymocytes with receptors capable of binding self-MHC molecules

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10
Q

Outcome of Negative selection in T cells

A

Self-tolerance
Selecting AGAINST thymocytes with high affinity receptors for self/MHC/self peptide complexes

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11
Q

What do cortical epithelial cells express high levels of

A

MHC 1 and 2

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12
Q

Outcome of TCR not binding to self-MHC molecules (positive selection)

A

Death by neglect

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13
Q

Outcome of TCR binding too strongly to self-MHC molecules

A

Cell death/apoptosis

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13
Q

Outcome of TCR binding with low affinity-just right to self-MHC molecules

A

Positive selection occurs, proceed to single-positive stage

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13
Q

Outcome of positive selection to MHC II

A

T cell becomes a SP CD4+ T cell

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14
Q

Outcome of Positive selection to MHC 1

A

T cell becomes a SP CD8+ T cell

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15
Q

Which cells express Autoimmune regulator (AIRE, transcription factor) (negative selection)

A

Medullary epithelial cells

16
Q

Main action of AIRE (autoimmune regulator) (negative selection)

A

Induce expression of many tissue-specific proteins in thymic epithelial cells (allows many peptides in to then be presented on MHC 1 and 2)

17
Q

What does AIRE permit (negative selection)

A

Allows T cells to be screened against self-antigens safely in thymus

18
Q

Outcome of TCR NOT binding to self-MHC molecules (negative selection)

A

Cells survive

19
Q

Outcomes of TCR binding to pMHC (negative selection)

A

1) Clonal deletion leading to death of self-reactive T cells
2) Clonal anergy (inactivation of autoreactive T cells)
3) Clonal editing (second or third chances at rearranging a non-self-reactive TCR gene)

20
Q

Where does Peripheral tolerance take place

A

In periphery
Circulation and secondary lymphoid organs

21
Q

Main action of Peripheral tolerance

A

Helps protect against autoreactive thymocytes that have escapes negative selection in thymus (induce anergy)

22
Q

Which cells help maintain peripheral tolerance

A

Regulatory T cells (Tregs)

23
Where does B cell development occur
Starts and majority is in bone marrow, but completed in periphery (including spleen)
24
Type of selection required for B cells
Negative selection (self-tolerance), no need for MHC restriction/positive selection
25
Outcomes of Negative selection in B cells (binding to pMHC)
1) Clonal deletion of strongly autoreactive cells (apoptosis) 2) Receptor editing (reactivation of recombination machinery) 3) Anergy (induction of nonresponsiveness to further stimuli)
26
How are self-antigens presented
Present on stromal cells and other cells or just soluble proteins in circulation
27
Where do B cells migrate for further maturation
The Spleen
28
Characteristics of Mature B cells
1) Express high levels of IgM/IgD on their surfaces 2) Negative selection (peripheral tolerance) 3) Recirculate between blood and lymphoid organs 4) Half life ~4.5 months in periphery
29
Where does receptor editing of potential autoreactive receptors happen
In light chains
30
What is central tolerance (negative selection)
Induction of immune tolerance IN primary lymphoid organs (bone marrow, thymus) through; Clonal deletion Receptor editing Clonal anergy
31
What is Peripheral tolerance
Induction of tolerance OUTSIDE primary lymphoid organs through; Anergy Deletion Immune regulation (Tregs)
32
Mechanisms of Central tolerance
1) Clonal deletion 2) Receptor editing 3) Clonal anergy
33
Mechanisms of Peripheral tolerance
1) Anergy 2) Deletion 3) Immune regulation (Tregs)
34
What is autoimmunity
A defect in tolerance
35
What is organ-specific autoimmunity
Predominant injury of AN (singular) organ or tissue
36
What is systemic autoimmunity
Injury of MANY (plural) different tissues
37
Types of mechanism of autoimmunity
1) Cell-mediated autoimmunity (T cells) 2) Antibody-mediated autoimmunity (antibodies)
38
Malfunction of Cell-mediated autoimmunity results in
Multiple sclerosis, Type 1 diabetes, etc
39
Malfunction of antibody-mediated autoimmunity results in
Lupus
40
How are the mechanisms of autoimmunity transferred
Cell-mediated autoimmunity--> T cell transfer Antibody-mediated autoimmunity-->Serum transfer