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Microbiology > Immunology > Flashcards

Immunology Flashcards

1
Q

What are Natural Killer (NK) cells?

A

NK cells are innate lymphocytes that play a crucial role in the immune response by recognizing and killing virus-infected cells and tumor cells without prior sensitization.

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2
Q

Which lineage do NK cells belong to?

A

NK cells belong to the lymphoid lineage, but they are part of the innate immune system.

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3
Q

What are the major surface markers of NK cells?

A

NK cells express CD16 and CD56 as their major markers.
Also CD94

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4
Q

What is the role of CD16 in NK cells?

A

CD16 (FcγRIII) mediates antibody-dependent cellular cytotoxicity (ADCC) by binding to the Fc portion of IgG.

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5
Q

What is the role of CD56 in NK cells?

A

CD56 is an adhesion molecule involved in NK cell activation and interaction with other immune cells.

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6
Q

Mechanism of NK cells

A

It has activating and inhibitory arm
Cells with MHC1 will get the inhibitory arm.
Cells with virus/ cancer won’t have MHC1 and it gets the activating arm which has NKG2D

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7
Q

Which cytokines activate NK cells?

A

IL-2, IL-12, IL-15, and IL-18 enhance NK cell activity.

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8
Q

What is the key difference between NK cells and cytotoxic T lymphocytes (CTLs)?

A

Unlike CTLs, NK cells do not require prior antigen exposure or MHC class I presentation to kill target cells.

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9
Q

What are the two main pathways by which NK cells induce apoptosis?

A

Perforin-granzyme pathway – Releases perforin to create pores and granzymes to induce apoptosis.

Fas-FasL pathway – NK cells express FasL, which binds to Fas on target cells, triggering apoptosis.

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10
Q

Which infections are more common in individuals with NK cell deficiency?

A

Individuals with NK cell deficiency are more susceptible to herpesviruses (e.g., CMV, HSV, EBV) due to impaired viral clearance.

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11
Q

Which clinical conditions are associated with defective NK cell function?

A

Severe herpesvirus infections (CMV, EBV, HSV)
Chronic lymphocytic leukemia (CLL)
Primary NK cell deficiency

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12
Q

What is the Pan T cell marker that carries the signal transduction molecule?

A

CD3

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13
Q

Helper T cell? Cytotoxic T cell?

A

CD4, CD8

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14
Q

Ratio of CD4 to CD8

A

CD4=2
CD8=1

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15
Q

If CD4:CD8 count is reducing, it is?
If CD4: CD8 count is increasing, it is?

A

HIV
Sarcoidosis

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16
Q

Where do T cells mature?

A

T cells mature in the thymus, where they undergo positive and negative selection.

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17
Q

What are the two main types of T cells?

A

CD4+ T helper cells (Th cells) – Help other immune cells by secreting cytokines.
CD8+ Cytotoxic T cells (CTLs) – Kill infected and cancerous cells.

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18
Q

What is the function of CD4+ T cells?

A

CD4+ T cells recognize MHC class II on antigen-presenting cells (APCs) and help coordinate the immune response through cytokine secretion.

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19
Q

What is the function of CD8+ T cells?

A

CD8+ T cells recognize MHC class I on infected or cancerous cells and kill them using perforin and granzyme-mediated apoptosis.

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20
Q

What is the role of regulatory T cells (Tregs)?

A

Tregs (CD4+CD25+FOXP3+) suppress excessive immune responses to maintain self-tolerance and prevent autoimmune diseases.

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21
Q

What are the key surface markers of T cells?

A

CD3 – TCR signaling complex (all T cells)
CD4 – Helper T cells (binds MHC II)
CD8 – Cytotoxic T cells (binds MHC I)
CD25 & FOXP3 – Regulatory T cells
CD28 – Co-stimulatory receptor for activation

22
Q

Which infections are associated with CD8+ T cell dysfunction?

A

HIV/AIDS – Causes CD8+ T cell exhaustion
Chronic hepatitis B/C – Leads to persistent CD8+ T cell activation and dysfunction

23
Q

Which genetic mutations cause T cell immunodeficiencies?

A

SCID (Severe Combined Immunodeficiency) – Defective T cell development

DiGeorge Syndrome – Thymic hypoplasia leading to T cell deficiency

FOXP3 mutations – IPEX syndrome (autoimmunity due to lack of Tregs)

24
Q

What are the major subsets of CD4+ T helper cells?

A

Th1 cells – Secrete IFN-γ, activate macrophages, and are involved in intracellular pathogen clearance.

Th2 cells – Secrete IL-4, IL-5, and IL-13 to promote B cell antibody production and eosinophilic response.

Th17 cells – Secrete IL-17 and IL-22 to enhance neutrophil responses against extracellular bacteria and fungi.

25
Q

What is the role of T cells in transplant rejection?

A

Acute rejection – CD8+ T cells attack donor tissue.
Chronic rejection – CD4+ T cells mediate chronic inflammation.

26
Q

What is the role of T cells in autoimmune diseases?

A

Th1 dominance → Type 1 diabetes, MS
Th17 dominance → Psoriasis, IBD
Treg dysfunction → Autoimmune polyendocrine syndromes

27
Q

What are the two main types of TCRs? (T cell Receptor)

A

αβ TCR – Found on most T cells, involved in adaptive immunity.
γδ TCR – Found in mucosal and epithelial tissues, involved in innate-like immunity.

28
Q

T cell CD markers

A

CD1-8, 28

29
Q

CD markers of B cell

A

CD10 (CALLA)
CD19, 20, 21, 22, 23
CD40
CD79a, 79b

30
Q

Pan B cell marker

A

CD19

31
Q

Signal transduction molecule for B cells

A

CD79

32
Q

How does EBV enter the B cell

A

CD21

33
Q

Interaction between B and T cells

A

B cells have CD40 and T cells have CD40 ligands. These interact and T cells produce IL-4
IL-4 changes IgM to IgG, A, M, E, D- This is called Isotype switching.
Defect in this causes Hyper IgM syndrome

34
Q

What is the Major Histocompatibility Complex (MHC)?

A

MHC is a set of cell surface proteins that present antigens to T cells

35
Q

What are the two main types of MHC molecules?

A

MHC Class I – Present on all nucleated cells; recognized by CD8+ T cells.
MHC Class II – Present on antigen-presenting cells (APCs); recognized by CD4+ T cells.

36
Q

Where are MHC genes located?

A

On chromosome 6, within the Human Leukocyte Antigen (HLA) complex.

37
Q

What are the genes encoding MHC Class II molecules?

A

HLA-DP, HLA-DQ, and HLA-DR.

38
Q

What are the genes encoding MHC Class I molecules?

A

HLA-A, HLA-B, and HLA-C.

39
Q

Which cells express MHC Class I?

A

All nucleated cells (except RBCs).

40
Q

Which cells express MHC Class II?

A

Antigen-presenting cells (APCs):

Dendritic cells (most potent APCs)
Macrophages
B cells

41
Q

What type of antigens does MHC Class I present?

A

Endogenous antigens (e.g., viral or tumor antigens).

42
Q

What type of antigens does MHC Class II present?

A

Exogenous antigens (e.g., bacterial toxins).

43
Q

HLA 3 makes ___

A

Complement proteins such as C2, C4, HSP, TNF alpha

44
Q

Antigen binding clefts in MHCs

A

MHC1- Alpha1 Alpha2 junction
MHC2- Alpha1 Beta2 junction

45
Q

What is the role of MHC in organ transplantation?

A

Mismatched MHC molecules can trigger graft rejection.
HLA matching is crucial for successful transplants.

46
Q

What is superantigen activation of MHC?

A

Superantigens (e.g., Staphylococcal enterotoxins) bind MHC II and TCR without antigen specificity, causing a cytokine storm (e.g., toxic shock syndrome).

47
Q

Which HLA types are associated with autoimmune diseases?

A

HLA-B27 → Ankylosing spondylitis
HLA-DR3/DR4 → Type 1 diabetes
HLA-DR4 → Rheumatoid arthritis
HLA-DR2 → Multiple sclerosis

48
Q

What is TAP deficiency (Bare Lymphocyte Syndrome Type I)?

A

A defect in TAP transporter prevents MHC I antigen loading, leading to recurrent viral infections.

49
Q

What is Bare Lymphocyte Syndrome Type II?

A

A defect in MHC II expression, leading to defective CD4+ T cell activation and severe immunodeficiency.

50
Q

Types of Hypersensitivity reactions

A

ACID
Anaphylaxis
Cytotoxic
Immune complex
Delayed

Microbiology (19 decks)

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