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Immunology > Failure of Host Defense Mechanisms > Flashcards

Failure of Host Defense Mechanisms Flashcards

1
Q

what are primary immunodeficiencies

A
  • 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
  • e.g. SCID
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4
Q

types of inherited of SCID

A

autosomal recessive: caused by ADA
x-linked: mutation in IL-2RG gene - affects cytokine receptors

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5
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 cause a defect in T-cell function
  • pyogenic bacteria cause a defect in antibody, complement or phagocyte function
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6
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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7
Q

what is the difference between the SCIDs ADA and Omenn syndrome

A

ADA: B and T cells affected
Omenn: T cells affected (autoreactive) + B cell development effected

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8
Q

what are the autosomal recessive SCIDs - (affect boys and girls + both B and T cells)

A

ADA and Omenn syndrome

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9
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
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10
Q

characteristics of Omenn syndrome

A
  • partial loss of V(D)J recombinase activity through mutations in at least one of RAG-1 or RAG-2 alleles
  • Peripheral T cells are autoreactive
  • impaired helper-T cells also indirectly impacts B cells
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11
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)
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12
Q

examples of immunodeficiencies that alter T-cell development and function

A

FOXN1 mutation
DiGeorge syndrome
Bare Lymphocyte syndrome (BLS)

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13
Q

FOXN1 mutation

A
  • lack of thymic function
  • abnormal T-cell development
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14
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
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15
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)
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16
Q

examples of immunodeficiencies that alter B-cell development

A

XLA
Hyper IgM syndrome
CVID

17
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
18
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
19
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
20
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.

21
Q

what are some immunodeficiencies of the innate immune system

A

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

22
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
23
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
24
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
25
Q

What are the mechanisms of immune evasion driven by genetic variation

A

antigenic variation
antigenic drift and shift

26
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
27
Q

antigenic drift and shift

A

drift: viral genome replicated and slowly accumulates mutations
shift: complete and sudden reassortment of the viral genome, creates a variant

28
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
29
Q

Acquired Immune Deficiency syndrome (AIDS)

A
  • major disease burden caused by HIV
  • CD4 T-cell count drops and leads to opprotunistic infections
30
Q

The virion of HIV

A
  • primary targets = T-helper cells
  • the protein gp120 on the vision surface recognizes CD4 (Th cell), CCR5 and CXCR4
31
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
32
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
33
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*
  5. viral assembly inhibitors
34
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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