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Immunology > Failure of Host Defense Mechanisms > Flashcards

Failure of Host Defense Mechanisms Flashcards

1
Q

what are primary immunodeficiencies

A
  • a heterogeneous group of inherited disorders with defects in one or more components of the immune system
  • moderately common
  • infections are hallmarks for PID
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2
Q

what are secondary immunodeficiencies

A
  • non-inherited, acquired
  • caused by environmental factors such as age, malnutrition, infection, irradiation, chemotherapy or exposure to toxins
  • infections are hallmarks
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3
Q

what are combined immunodeficiencies

A
  • impairments in both B-cells and T-cells due to inherited mutations
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4
Q

characteristics of primary immunedeficiencies

A
  • inherited gene variants (caused by mutatuons
  • recurrent infections early in life
  • often X-linked (affect mostly males)
  • affect 1 in 1000 people
  • fungal or viral infections caused by defect in T-cell fuunction
  • pyogenic bacteria cause a defect in antibody, complement or phagocyte function
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5
Q

what are the 9 categories of human immunodeficiency syndromes

A
  1. CID limited to the immune system
  2. CID with defects on tissues outside the immune system
  3. Antibody deficiencies
  4. immune dysregulation
  5. Phagocyte defects
  6. Innate immunity defects
  7. Autoinflammatory disorders
  8. complement deficiencies
  9. Phenocopies of inborn errors of immunity
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6
Q
  1. combined immunodeficiencies (CIDs) limited to the immune system
A

yc deficiency
RAG-1 or RAG-2 deficiency

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7
Q
  1. CIDs with defects in tissues outside the immune system
A

FOXN1 deficiency (nude phenotype)
Job syndrome

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8
Q
  1. Antibody deficiencies
A

Burton’s X-linked agammaglobulinemia (XLA)
AID deficiency
Selective IgA deficiency

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9
Q
  1. immune dysregulation
A

Perforin deficiency
IL-10 deficiency

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10
Q
  1. Phagocyte defects
A

elastase deficiency
GATA2 deficiency

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11
Q
  1. Innate immunity defects
A

IL-12p40 deficiency
IFN-y receptor 1 deficiency

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12
Q
  1. Autoinflammatory disorders
A

Muckle-Wells syndrome

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13
Q
  1. complement deficiencies
A

C1q deficiency
MASP deficiency

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14
Q
  1. Phenocopies of inborn errors of immunity
A

APECED syndrome

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15
Q

what is the difference between the SCIDs ADA and Omenn syndrome

A

ADA: B and T cells affected
Omenn: T cells affected

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16
Q

what are the autosomal recessive SCIDs - (affect boys and girls)

A

ADA and Omenn syndrome

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17
Q

characteristics of ADA (adenosine deaminase deficiency)

A
  • disrupts the S-phase of the cell cycle
  • improper lymphocyte development - lack of T and B cells
  • causes SCID in infancy
  • must be treated with bone marrow transplant
18
Q

characteristics of Omenn syndrome

A
  • partial lose of V(D)J recombinase activity through mutations in at least one of RAG-1 or RAG-2 alleles
  • Peripheral T cells are autoreactive
19
Q

x-linked SCID characteristics

A
  • presents with lack of peripheral blood T cells and NK cells
  • B cells are usually present but Ig production is decreased
  • caused by mutation in IL-2RG (gene that encodes common gamma chain - yc - of cytokine receptors)
20
Q

examples of immunodeficiencies that alter T-cell development and function

A

FOXN1 mutation
DiGeorge syndrome
Bare Lymphocyte syndrome (BLS)

21
Q

FOXN1 mutation

A
  • lack of thymic function
  • abnormal T-cell development
22
Q

DiGeorge syndrome

A
  • small portion of chromosome 22 is deleted
  • thymus is absent - abnormal T-cell development and function
  • loss of T cells is very difficult to treat
23
Q

Bare lymphocyte syndrome (BLS)

A
  • MHC I or II deficiency
  • mutations in TAP genes cause improper activation of CD8 T cells (MHC I)
  • mutations in TFs responsible for MHC II expression cause improper activation of CD4 T cells (MHC II)
24
Q

examples of immunodeficiencies that alter B-cell development

A

XLA
Hyper IgM syndrome
CVID

25
Q

X-linked Agammaglobulinemia (XLA)

A
  • defect in B cell development due to mutation in the BTK gene on X-chromosome
  • low levels of all Ab isotypes
  • reduced B cell numbers
  • women not usually affected because they are XX and disease is recessive
  • B-cell development is arrested in XLA male or carrier female if normal X is inactivated
26
Q

Hyper IgM syndrome

A
  • affects Igs and impacts only males
  • caused by mutation in the CD40 ligand gene (on activated T-helper cells)
  • low levels of IgG, IgA and IgE
  • tightened susceptibility to infections that require high-affinity, class-switched antibodies for clearance
27
Q

common variable immunodeficiency (CVID)

A
  • most common form of primary ID
  • variable deficiencies in 2 or more Ig isotypes
  • low IgG and IgA, with or without low IgM
  • mutates BAF receptor - needed for affinity maturation and to provide survival signal
28
Q

Defects at different stages of the complement system

A

classical activation: immune-complex disease
lectin activation: bacterial infections (mainly in childhood)
alternative activation: infection with pyrogenic bacteria, but no immune complex disease
C3b deposition: pyogenic bacteria infection, sometimes immune-complex disease
MAC: infection with Neisseria spp.

29
Q

what are some immunodeficiencies of the innate immune system

A

Chronic granulomatous Disorder (CGD)
Leukocyte Adhesion Deficiency (LAD) I
Chediak-Higashi Syndrome

30
Q

chronic granulomatous disorder (CGD)

A
  • causes defect in phagocytes
  • phagocytic cells cannot kill certain pathogens - form gransulomas
  • defective production of ROS
  • patients vulnerable to severe recurrent bacterial and fungal infections
31
Q

Leukocyte Adhesion Deficiency (LAD) I

A
  • defect in migration of phagocytes (neutrophils)
    reduced or absent expression of B2 integrins on leukocytes
  • patients deficient in expression of the 3 integrins containing CD18 (LFA-1, Mac-1, Gp 150/95)
  • normal expression of selectin ligand PSGL-1
  • if they can’t get into tissues then infection persists
32
Q

Chediak-Higashi Syndrome

A
  • defects in phagocytes
  • impaired lysis of phagocytosed bacteria - recurrent bacterial respiratory infections
  • mutation in CHS gene - affects synthesis of storage/secretory granules
  • abnormal NK cell function
    defective lysosomal function in macrophages, DCs abdominal neutrophils
  • hypopigmentation of skin eyes and hair - albinism
33
Q

What are the mechanisms of immune evasion driven by genetic variation

A

antigenic variation
antigenic drift and shift

34
Q

antigenic variation

A
  • pathogen express different surface antigens without changing bacterial genus and species
  • many species have multiple serotypes which differ on the surface, therefore not recognized by the same immunoglobulins
35
Q

antigenic drift and shift

A

drift: virus has a new genetic makeup from slowly accumulated mutations
shift: complete reassortment of the viral genome, creates a variant, how epidemics start

36
Q

what is viral latency

A
  • when a virus incorporates their viral genomes into target cells and undergo a dormant state
  • in this dormant state the viral genome is present but host cells lower their production of viral particles
  • reactivation of viral genome is pathogen specific
  • e.g. HIV and the herpes simplex virus
  • in primary infection of the trigeminal ganglion we get cold sores
37
Q

Acquired Immune Deficiency syndrome (AIDS)

A

a major disease burden caused by HIV infection

38
Q

The vision of HIV

A
  • primary targets = T-helper cells
  • the protein gp120 on the vision surface recognizes CD4 (Th cell), CCR5 and CXCR4
39
Q

The life cycle of HIV - pathway

A
  • virus binds CD4 and co-receptor on helper T cell via gp120
  • viral envelope fuses with cell membrane and viral genome enters cell
  • reverse transcriptase copies viral RNA into double-stranded cDNA
  • viral cDNA enters nucleus and is integrated in host DNA
  • T-cell activation induces low-level transcription of provirus
  • RNA transcripts are spliced allowing translation of tat and rev genes
  • tat amplifies transcription of viral RNA, rev increases transport of viral RNA to cytoplasm
  • the late proteins Gag, Pol and Env are translated and assembled into virus particles which bud from the cell
40
Q

what is the typical course of an untreated HIV infection

A
  • after initial infection with HIV, viral genome increases dramatically
  • there’s an initial decrease in CD4 T cells until viral latency
  • viral titer remains unchanged but CD4 T cells continue to decrease
  • if untreated, CD4 T cell levels are so low that infection by opprotunistic pathogens occurs until the patient succumbs
41
Q

Targets for therapeutic drugs to interfere with the HIV life cycle

A
  1. viral entry inhibitors
  2. reverse transcriptase inhibitors
  3. viral integrase inhibitors
  4. protease inhibitors
42
Q

pathogenic bacteria target _____ to subvert immunity

A

the complement cascade
- at activation, convertase formation or MAC assembly

Immunology (22 decks)

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