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PHGY 209 > Immunology II > Flashcards

Immunology II Flashcards

1
Q

What are the two components of the second line of defense of the innate immune system?

A

Humoral and cellular factors.

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2
Q

The major cellular factors in the second line of defense are […]

A

Natural killer (NK) cells and phagocytes

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3
Q

What are NK cells?

A

Natural killer cells are a class of lymphocytes that target virus-infected cells and cancer cells.

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4
Q

Are NK cells antigen-specific?

A

No, they do not need to recognize a specific antigen.

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5
Q

NK cells kill infected cells by […]

A

Binding to them and releasing perforins and granzymes.

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6
Q

Explain how the NK cell knows which cells to kill.

A

On normal, nucleated body cells, MHC Class 1 proteins are expressed. The NK cell recognizes this and this tells it not to kill the normal cell. When a cell gets infected, it downregulates the MHC Class 1, so the NK cell gets activated and releases the perforrins and granzymes to kill it.

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7
Q

What is the function of phagocytes?

A

They non-specifically engulf microbial invaders.

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8
Q

What are the two types of phagocytes? Explain the major difference between them.

A

Fixed-tissue macrophages and dendritic cells, which come from monocytes and are sitting at barrier tissues waiting for infection to arrive, and neutrophils, which get recruited to the site of injury.

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9
Q

Name the four steps of phagocytosis and intracellular destruction of a microbe.

A

Adherence, ingestion, digestion, killing

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10
Q

Explain the process of phagocytosis and intracellular destruction of a microbe.

A

The macrophage recognizes the bacteria using things like complements and takes it in via endocytosis. Once in the cell, the bacteria enters a membrane-bound compartment called the phagosome. The phagosome fuses with the lysosome to form the phagolysosome. Because lysosomes have a low pH, enzymes, hydrogen peroxide and nitrogen oxide, the bacteria can be degraded in the phagolysosome. Some components are reused while others are released as signaling to other cells.

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11
Q

How do phagocytes recognize microbes?

A

Since they are part of the innate immune system, which is non-specific, they detect unique, conserved structures that are essential to microbial physiology and that would not be found in a mammalian cell, such as a cell wall. These are called pathogen-associated molecular patterns (PAMPs).

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12
Q

Give two examples of PAMPs

A

Lipopolysaccharide of gram-negative bacteria, peptidoglycan of gram-positive bacteria

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13
Q

Macrophages recognize PAMPs using […]

A

Immune system receptors called Pattern Recognition Receptors (PRR), which includes Toll-like receptors. These are found on the surface of the macrophage.

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14
Q

What are toll-like receptors?

A

They are a family of highly conserved transmembrane receptors essential for microbial recognition via PAMPs by macrophages.

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15
Q

Describe the structure of toll-like receptors.

A

They have an extracellular domain, which is used to recognize the presence of a pathogen, and an intracellular domain, which is used to send downstream signals to other cells to activate processes that will lead to the ingestion and killing of bacteria.

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16
Q

When toll-like receptors detect […], this starts the process of […]

A

PAMPs, inflammation

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17
Q

Explain what happens when PAMPs get detected by toll-like receptors.

A

The macrophage is activated and signals are sent out to the body to active the inflammation process and recruit more immune cells to the site of injury, including neutrophils.

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18
Q

The first cell to be recruited once the process of inflammation has begun is […]

A

The neutrophil

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19
Q

The recruitment of neutrophils corresponds to the […] stage of inflammation

A

Emigration of phagocytes

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20
Q

Explain the first step in the emigration of phagocytes to the injured site.

A

The first step is chemotaxis. Once the toll-like receptors have detected PAMPs, they send out chemoattractants, which attract phagocytes (neutrophils) to the injured site.

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21
Q

Explain the second step in the emigration of phagocytes to the injured site.

A

The second step is margination. The composition of the endothelium of the capillary changes such that neutrophils roll along it and start to pile up near the injury.

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22
Q

Explain the third step in the emigration of phagocytes to the injured site.

A

It is diapedesis. Spaces develop between the endothelial cells of the capillary due to increased blood flow and the neutrophils can now pass through and enter the tissue to go to the injury to kill bacteria.

23
Q

Once the neutrophils have arrived at the injury site, explain what their function is.

A

Most die in the process of killing bacteria, and when they die they form a NET (neutrophil extracellular traps), which is sticky and traps microbes in place to prevent them from travelling further.

24
Q

NETs are made of […]

A

Processed chromatin bound to cytoplasmic proteins which come from lysed neutrophils.

25
Q

NETs lead to the production of […]

A

Pus

26
Q

Pus is comprised of […]

A

A mixture of dead bacteria and neutrophils.

27
Q

What happens once the neutrophils have completed their role of creating the NET?

A

The specific branch of the immune system is activated.

28
Q

Explain how the specific branch of the immune system is activated.

A

When the neutrophils start dying and the NET is produced, more signals are sent to the immune system so that antigen-presenting cells, macrophages and dendritic cells, move into the tissue to pick up bacterial material and transport it to the regional lymph node.

29
Q

When phagocytes transport bacteria from the injury to the regional lymph node, they travel via the […], because […]

A

Lymph, because they don’t want to carry the bacteria directly in the blood.

30
Q

Name 3 other terms for antigen.

A

Immunogen, allergen, ligand

31
Q

What is an antigen?

A

It is an antibody generator (can be the bacteria) which produces an immune response.

32
Q

The part of the antigen that is recognized by immune cells is the […]

A

Epitope

33
Q

The transition from non-specific immunity to specific immunity occurs via […]

A

Antigen presentation by phagocytes (association of MHC-II + antigen)

34
Q

Explain what is meant by antigen presentation via phagocytes.

A

The phagocytes (particularly dendritic cells and macrophages) are going to move into the area of infection, ingest some of these bacteria, and they die inside the cell. They will put some of the bacteria on their surface. There will be alive or dead bacteria stuck to them and they will travel via the lymphatic system back to the regional lymph node. This is where most of the immune cells are present, so it brings the antigen into this region. This activates the specific immune response.

35
Q

Specific/adaptive immunity is mediated by […]

A

Antibodies or cells

36
Q

What are the two components of specific/adaptive immunity?

A

Humoral - antibody-mediated immunity and cell-mediated immunity

37
Q

What type of cell is involved in humoral specific/adaptive immunity? Explain how.

A

B cells. They are activated in the lymph node and transform into a plasma cell, which will produce lots of antibodies and complement to kill. They will also form memory B cells, which allow protection to the same pathogen in the future.

38
Q

What type of cell is involved in cell-mediated specific/adaptive immunity? Explain how.

A

Cytotoxic T cells. They kill infected body cells, cancer cells, and foreign cells.

39
Q

What are the two classes of MHCs? Explain the difference between them.

A

MHC-I, which is expressed on all nucleated cells, and MHC-II, which is expressed on antigen-presenting cells.

40
Q

Antigen-presenting cells include […]

A

B-cells, macrophages, and dendritic cells

41
Q

Describe the structure of MHCs.

A

They are transmembrane proteins with an extracellular component that allows them to carry peptides. This is important for their recognition by immune cells.

42
Q

Do RBCs have MHCs on their surface? Explain.

A

No, because they have no nucleus, therefore no MHC-I, and are not antigen-presenting cells, therefore no MHC-II. They are recognized in a different way.

43
Q

Describe the purpose of MHC-II in the specific immune system.

A

It is essential in the antigen presentation process. T-cell receptors only recognize antigens when they are associated with MHC-II proteins on antigen-presenting cells.

44
Q

Explain the process through which MHC-II becomes associated with antigens.

A

In antigen-presenting cells, the microbe (antigen) is taken into an APC and enters a phagosome or endosome, which digests it into peptide fragments. As this is happening, MHC-II molecules are synthesized in the ER and are packaging into a vesicle. The MHC-II vesicles fuse with the antigen peptide fragment vesicles, and then the antigen fragments bind to MHC-II molecules. The vesicle then undergoes exocytosis and antigen-MHC-II complexes are inserted in the plasma membrane of the antigen-presenting cell.

45
Q

The dendritic cell is also referred to as the […], because […]

A

Professional antigen-presenting cell, because dendritic cells are most often the ones that present the antigen to the immune system.

46
Q

What are the three stages of a typical adaptive immune response to an antigen?

A

The encounter and recognition of an antigen by lymphocytes
Lymphocyte activation (recognition of MHC-II)
The attack launched by the activated lymphocytes and their secretions

47
Q

The adaptive immune system involves which cells?

A

B cells and T cells.

48
Q

What is the role of T cells in the adaptive immune system?

A

They are responsible for the cell-mediated portion. Cytotoxic T cells attack infected body cells, cancer cells, foreign cells, etc.

49
Q

Explain what happens to B and T cells once they enter the secondary lymphoid organs.

A

B cells, when activated by antigen, will divide and transform into plasma cells, which produce antibodies. Cytotoxic and helper T-cells will also divide when activated by antigen.

50
Q

Helper T-cells are also referred to as […]. Cytotoxic T-cells are also referred to as […]

A

CD4+ cells, CD8+ cells

51
Q

Explain how helper T cells, B cells, and cytotoxic T cells interact after encountering an antigen.

A

The helper T cell will respond first and divide. They will then release cytokines that activate the transformation of the B cell into plasma cells and the replication of the CD8+ cell.

52
Q

How do T-cells and B-cells recognize specific microbes in order to develop the correct immune response?

A

We have millions of different types of T-cells and B-cells that can recognize different microbes, as they have different receptors. They are circulating, waiting for a match.
How do they find a match? The dendritic cells pick up pathogens and put them on their surface, and that’s what going to lead to interactions with the helper T cells and B cells.

53
Q

Describe the match between a T helper cell and an antigen presenting cell.

A

The T cell receptor, which is designed for a particular peptide (coming from a particular antigen), will bind to the corresponding MHC-II + peptide complex of the antigen-presenting cell. Co-reception is also required between the B7 protein on the dendritic cell and the CD28 protein on the T-helper cell. This leads to the activation of the T-cell.

54
Q

What is the role of B cells in the adaptive immune system?

A

They are responsible for the humoral portion. They transform into plasma cells and produce antibodies. They use antibodies and complement to kill.

PHGY 209 (33 decks)

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