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Immunology COM > Cells and Signals of the Immune System > Flashcards

Cells and Signals of the Immune System Flashcards

1
Q

Adaptive Immunity is composed of two responses. What cells mediate each response?

A
  1. Humoral immunity is mediated by B lymphocytes

2. Cell-mediated immunity is mediated by T lymphocytes (also macrophages, NK cells)

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2
Q

B and T cell proliferation in early lymphocte maturation is stimulated by which cytokine?

A

IL-7

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3
Q

What interacts with the T-cell receptor (TCR) of an immature, double positive T cell (CD4+/CD8+ to signal differentiation into a single positive cell? In what organ does this occur?

A

Interaction with either major histocompatibility complex I (MHC I) (CD8+) or MHC II (CD4+) in the coretex of the thymus

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4
Q

What two processes eliminate immature T cells lacking proper antigen receptor specificities?

A
  1. Positive selection selects for lymphocytes with TCRs that recognize self-MHC proteins, ensuring that only T cells with TCR that recognize MHC mature.
  2. Negative selection eliminates autoreactive T cells that bind to MHC with high affinity.
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5
Q

What mechanism drives cell elimination in positive selection?

A

T cells that cannot bind to self-MHC molecules undergo apoptosis

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6
Q

Apoptosis of T-helper cells (CD4+, Th) or cytotoxic T cells (CD8+, Tc) bearing TCRs for self-proteins is the result of what process?

A

Tolerance, which prevents autoimmune reactions

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7
Q

What cytokine released by activated Th further stimulates Th-cell survival/proliferation?

A

IL-2. It binds to the IL-2receptor on Th cells causing further proliferation

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8
Q

Name the two signals that are needed to activate T cells:

A
  1. The first signal is the MHC/antigen complex interaction with a TCR specific for that antigen
  2. The second is the costimulatory signal of the CD28 protein on the T cell with the B7 protein on the antigen presenting cells (APC)
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9
Q

What is the result of an interaction between a T cell and an APC in the absence of costimulation?

A

Anergy or unresponsiveness of T cells

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10
Q

What T-cell protein displaces CD28 from B7, inhibiting T-cell activation and ensuring T cell homeostasis?

A

Cytotoxic T lymphocyte antigen 4 (CTLA-4)

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11
Q

Which MHC class molecule presents processed antigens from organisms that have been phagocytosed? What cells possess this MHC class?

A

MHC-II complexes on professional APC present extracellular, phagocytosed proteins to Th cells

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12
Q

What cells function as professional APCs?

A

Dendritic cells, macrophages, and B cells

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13
Q

What is the source of antigen presented by MHC-I molecules? What cells possess this class?

A

MHC-I complexes on ALL nucleated cells present intracellular proteins proteins to Tc cells

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14
Q

What is the cluster of polypeptides present in all T cells that is important in signal transduction by the TCR?

A

CD3 complex

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15
Q

Induction of which of the T-cell helper lines (Th1 or Th2) elicits a more effective response against intracellular pathogens such as Mycobacterium tuberculosis?

A

Th1 cells are more effective against intracellular pathogens

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16
Q

Which cytokine released by Th1 cells is involved in macrophage activation?

A

gamma-Interferon (y-INF)

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17
Q

What other signaling pathway results in macrophage activation?

A

The interaction of CD40 on macrophages with CD40L on T cells

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18
Q

What transcription factor is involved in both INF-y and CD40/CD40L signaling?

A

Nuclear factor-kB

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19
Q

How do macrophages respond to y-INF and CD40/CD40L signaling?

A

Cytokine release, increased microbicidal activity, increased phagocytic activity (through upregulation of B7and MHC II)

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20
Q

Once activated, what are the major cytokines released by macrophages?

A 
Tumor necrosis factor (TNF)
IL-1
IL-8 (leukocyte recruitment)
IL-6 (lymphocyte activation
IL-12 (Th1 differentiation)
21
Q

What are the microbicidal substances produced by activated macrophages?

A

Reactive oxygen species, nitric oxide, and lysosomal enzymes

22
Q

What are the main effector cells and cytokines of delayed hypersensitivity?

A

Macrophages induce differentiation of naive Th cells into Th1 cells by secretion of IL-12. IL-12 acts on NK cells to produce y-INF which also promotes Th1 differentiation. Th1 cells in turn release y-INF, activating macrophages

23
Q

Against what pathogens is delayed hypersensitivity needed?

A

Intracellular pathogens (eg. M tuberculosis, Salmonella typhimurium, and Histoplasma)

24
Q

Patients with T-cell deficiencies are most susceptible to what families of pathogens?

A

All severe T-cell deficiencies leave patients particularly susceptible to mycobacterial, viral and fungal infections

25
Q

What is the result of superantigen activation of Th cells?

A

Massive Th-cell activation and cytokine release, resulting in shock

26
Q

Which cytokine induces naive Th cells into mature Th2 cells?

A

IL-4

27
Q

What cytokines do Th2 cells produce? What properties do these cytokines share?

A

IL-4, IL-5, IL-10, and IL-13. All are anti-inflammatory and antagonize Th1 cells

28
Q

Which cytokines aid B cells in antibody production?

A

IL-4 and IL-5

29
Q

What functions do IL-4 and IL-5 from Th2 cells serve in helminth immunity?

A

IL-4 induces hellminth specific immunoglobulin (IgE) abs and IL-5 activates eiosinophils

30
Q

Which cytokine is implicated as a mediator of asthma (airway hyperresponsiveness)?

A

IL-13

31
Q

By what two main methods do CD8+ cells kill virus-infected, graft, and tumor cells?

A

Cytotoxic T cells can lyse infected cells or induce apoptosis

32
Q

Which mature immune cell has receptors for while, unprocessed antigens and does not require MHC presentation?

A

B cells, which actually present antigens themselves via MHC II to CD4+ helper cells in the process of activation, can recognize soluble or cell-associated antigens

33
Q

Which types of antigens can induce ab production by B cells without the aid of helper T cells (ie, T-cell independent response)?

A

Multivalent antigens (bacterial capsule polysaccharides, DNA, RNA, and lipids) bind many IgM (immunoglobulin M) molecules and cross-link IgM receptors on B cells

34
Q

Where does B cell differentiation occur?

A

Bone marrow

35
Q

What is the predominant ab released in the initial stages of the primary humoral response?

A

IgM. Following a lag phase either IgG, IgA or IgE appear in the secondary response

36
Q

What is class switching of antibodies?

A

The process that changes IgM to IgG, IgA or IgE

37
Q

What cells and signals are involved in class switching?

A

Th-cell CD40 ligand interacts with B-cell CD40, inducing the release of IL-4, IL-5, and INF-y which signals class switching

38
Q

X-linked hyper-IgM syndrome is an inherited disorder where the CD40 ligand on T cells is defective. How would this affect B cells?

A

Inability to perform isotype switching resulting in hypersecretion of IgM

39
Q

How would the same syndrome (hyper IgM) affect macrophages?

A

The CD40-CD40L interaction is necessary for macrophage activation by T cells. Macrophages cannot be activated, resulting in susceptibility to intracellular microbes

40
Q

What are the main steps in B-cell presentation to antigens to helper T cells?

A

Antigen-specific B cells bind to native antigen with membrane-bound immunoglobulin molecules. After internalization and processing of the antigen in an endosome, epitopes are presented on the B-cell surface via an MHC-II molecule where it is then presented to T cell

41
Q

One of the causes of severe combined immunideficiency (SCID) is a lack of functional IL-7 receptors. What cells are depleted? How is immunity affected?

A

Since T cells require IL-7 for development, both cell mediated and humoral responses would be diminished

42
Q

What would be different about the T cells in a patient with DiGeorge syndrome compared to that of a person without it? (DiGeorge syndrome results in thymic hypoplasia)

A

T cell differentiate in the thymus; abnormal thymic structure would result in a lack of T cells

43
Q

What immune cell kills infected cells lacking MHC-I proteins?

A

NK cells destroy infected cells that lose the ability to synthesize MHC-I proteins

44
Q

NK cells are activated by which cytokines?

A

IL-12 and y-INF

45
Q

Which cytokines are responsible for the increased production of C-reactive protein during an acute-phase response in innate immunity?

A

IL-1, TNF-a, and IL-6 induce the liver to produce C-reactive protein

46
Q

What cytokine is chemotactic for neutrophils?

A

IL-8 along with a complement component (C5a)

47
Q

Which cytokine has a similar function to granulocyte-macrophage colony stimulating factor (GM-CSF)?

A

IL-3 is made by activated Th cells and supports growth and differentiation of bone marrow stem cells

48
Q

The two types of immunity are innate and adaptive immunity. What cells mediate innate immunity?

A

Monocytes/Macrophages, neutrophils, natural killer (NK) cells, gamma-delta T cells

Immunology COM (11 decks)

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