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Infectious Diseases 2 > 2. Antigen processing & Presentation > Flashcards

2. Antigen processing & Presentation Flashcards

1
Q

What are the three major classifications of cell types involved in the immune response?

A
  • Polymorphonuclear leukocytes PMNs (granulocytes)
  • Monocytes
  • Lymphocytes
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2
Q

Which cell type can be considered the first line of defence against an invading pathogen?

A

PMNs

  • Neutrophils in particular
  • Drawn towards infection by chemotaxis
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3
Q

Describe PMNs…

A
  • Can discriminate between self and nonself
  • Not programmed to ingest specific antigens
  • Ingestion is facilitated when the antigen is coated by antibody or by complement protein
  • Don’t possess immunological memory
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4
Q

What are the two types of T helper cells and what do they do?

A

Th1: Promotes cell mediated immunity

Th2: Promotes antibody production

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5
Q

Describe Neutrophils…

A
  • Lifespan of only a few days
  • Contain primary and secondary granules in their cytoplasm
  • Possess many receptors on the cell surface
  • Receptors for Ig
  • Capture foreign material through phagocytosis
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6
Q

Describe the process of Neutrophils phagocytosing…

A
  1. Chemotaxis
  2. Adherence & Opsonization
  3. Ingestion
  4. Digestion
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7
Q

What is the fate of neutrophils?

A
  • They are capable of undertaking only a limited number of phagocytic events
  • After phagocytosis many undergo apoptosis and are removed by macrophages
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8
Q

What is Opsonization?

A

Coating of a particle with molecules that promote phagocytosis
- molecules are called opsonins

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9
Q

What are the three major types of PMNs?

A
  1. Neutrophils
  2. Eosinophils
  3. Basophils
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10
Q

Describe Eosinophils…

A
  • Second major PMN
  • 12 day half life in tissues
  • 30s half life in circulation
  • Phagocytic cells that can ingest and destroy foreign material
  • More effective in the extracellular digestion/ damage of infectious agents
  • Contain two types of granules
  • Possess surface receptors for immunoglobulin and complement
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11
Q

What is the major function of Eosinophils?

A

The destruction of parasitic helminths
- Antibody coated parasites attach to the eosinophil which degranulates and releases its granule contents into the worm cuticle

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12
Q

Describe Basophils…

A
  • PMN
  • Found primarily circulating in the blood
  • Contains a complex of vasoactive molecules
  • Have high affinity IgE receptors on their cell surface
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13
Q

What are lymphocytes…

A

Cells that originate from bone marrow and lymphoid stem cells

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14
Q

What are the primary lymphoid organs?

A

Organs that regulate the production and differentiation of lymphocytes

  • Thymus
  • Bursa (birds)
  • Peyer’s patches
  • Bone marrow
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15
Q

What are the secondary lymphoid organs?

A

Tissues where antigen processing occurs and where lymphocytes respond to antigen

  • Tonsils
  • Spleen
  • Peyer’s patches
  • Bone marrow
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16
Q

How can B cells and T cells be differentiated from each other?

A

By their surface components (antigens and receptors)

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17
Q

Describe a B cell receptor…

A

BCR

  • Consists of antibody molecules bound to the cell membrane in such a way that they are able to bind antigen to the B cell surface
  • Can bind to free antigen molecules
18
Q

Describe a T cell receptor…

A

TCR

  • Not an immunoglobulin molecule
  • Always associated with a protein called CD3
  • Found on all T cells and not on any other cell type
  • Can only bind to processed antigen that is associated with MHC molecules on the surfaces of APCs
19
Q

CD4+8-

A

T helper cell

  • CD4
  • Involved in positive regulation of the acquired immune system
  • Without them, the immune response to a particular foreign antigen would be weak/ non-existent
  • Able to communicate with other cells of the immune response and activate/ regulate them by cytokine release
  • TH1 and TH2 cells secrete different sets of cytokines
20
Q

CD4-8+

A

Cytotoxic T cell

  • CD8
  • Lytic capability
  • Important for the recognition and elimination of virus infected and tumour cells
  • Requires antigen to be presented to them by MHC I molecules on other cells
21
Q

Describe TH1 cytokines…

A

Key mediators of cell-mediated immunity

e.g. macrophage activation and delayed-type hypersensitivity

22
Q

Describe TH2 cytokines…

A

Stimulate B cell proliferation and immunoglobulin secretion

23
Q

What are regulatory T cells?

A

T cells that are involved in controlling the intensity of the immune response
- Secrete cytokines that turn down the immune system

24
Q

What is a Natural T reg cell?

A

T cells that originate in thymus and are present in the host before pathogen exposure

25
Q

What is an Inducible Treg cell?

A

T cell produced in the secondary lymphoid tissue and acquire regulatory functions in the context of a given infection

26
Q

What are natural killer cells?

A

A subset of lymphocytes that arise from precursor cells in the bone marrow

  • Present in blood, bone marrow and spleen
  • Defense against viral infection
  • May have a role in immune surveillance to protect against metastasis of tumours
27
Q

What are the three major routes an antigen can follow once it gains access to the body?

A
  1. Access via the bloodstream
  2. Access via epidermal, dermal or subcut tissue
  3. Access via GIT or respiratory tract
28
Q

Describe monocytes…

A
  • Develop from immature hematopoietic progenitor cells in the bone marrow
  • Progenitor cell is the monoblast which develops into a promonocyte then into a monocyte
  • Mature monocytes enter the circulation
29
Q

Where are MHC I found?

A

On the surface of most nucleated cells (including APCs)

30
Q

Where are MHC II found?

A

Only on the surface of lymphocytes, dendritic cells an macrophages

31
Q

Where are MHC III found?

A

Not found specifically on cell surfaces

32
Q

What is a thymus dependent antigen?

A

Molecules that are composed of repeating units that can directly trigger the antibody producing B cell to produce IgM

33
Q

When does the T helper cell recognise an antigen?

A

Only when it is together with MHC antigens on the surface of the APC
- Ensures no self antigens evoke an immune response

34
Q

What happens once an antigen has been recognised?

A

the antigen is fragmented in an acidic compartment that is produced when the endosome fuses with the lysosome
- Here the individual epitopes from the antigen are thought to become associated with MHC II

35
Q

What are the three major functions of dendritic cells?

A
  1. Act as sentinel cells and activate immune responses
  2. Process exogenous antigen for presentation to T cells
  3. Direct the emphasis of the immune response to be predominantly antigen mediated or cell mediated
36
Q

What are plasmacytoid dendritic cells?

A

Found in blood, bone marrow and lymphoid tissue

- derived from lymphoid precursor

37
Q

What are myeloid dendritic cells?

A

Differentiate from blood monocytes

- Derived from myeloid precursor

38
Q

What are follicular dendritic cells?

A

Found in secondary lymphoid organs

- Derived from myeloid precursor

39
Q

What are langerhaans cells?

A

Found in epidermis and mucous membranes

  • Derived from myeloid precursor
  • They can pick up and process antigen and travel to lymph nodes where they present antigen to activate T cells
40
Q

What does a T helper cell require for it to become activated?

A
  • Binding of TCR to MHC II on the APC

- Cytokines

41
Q

What happens when T cells kill?

A

They exocytose granules that release their contents (cytotoxins) into the intracellular space between the target cell and the effector

  • Among granule contents are proteases which degrade proteins
  • Apoptosis can also be triggered
42
Q

What is the sequence of events that occur to initiate the antibody production by plasma cells?

A
  1. T helper cell activated following antigen presentation by APC
  2. Relevant B cells are engaging antigens through their immunoglobulin receptors
  3. Antigen-receptor complex is drawn into the cell by endocytosis
  4. Full activation of B cell is achieved when cytokine signals are provided by a T helper cell
  5. B cells also function as APCs
  6. Effector T cells can then deliver the appropriate cytokines that can affect other T and B cells that are in close proximity

Infectious Diseases 2 (9 decks)

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