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BDS2 PMI > PMI02-3002 > Flashcards

PMI02-3002 Flashcards

1
Q

What are the four main components of the immune system?

A

T cells

B cells

Phagocytes

Complement

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2
Q

What is immunodeficiency?

A

Disease that is the result of loss of function/defective function/absence of a component of the immune system

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3
Q

What are primary and secondary immunodeficiencies?

A

Primary = genetically determined or result of developmental anomalies, rare

Secondary = acquired, caused by disease or immunosuppressive treatment, more common

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4
Q

What complement deficiencies can occur?

A

C1q/r/s, C2 or C4 deficiency (immune complex disease)

C3 deficiency

Factor B or D or properdin deficiency (similar to but not immune complex disease)

MAC deficiency

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5
Q

What is immune complex disease?

A

Inability to remove immune complexes with deficiencies in C1q/r/s or C2 or C4 (classical pathway)

Susceptibility to encapsulated organisms (S.pneumoniae, Neisseria)

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6
Q

What is the effect of a C3 deficiency?

A

Defective opsonisation so compromised removal via phagocytosis

Susceptibility to encapsulated organisms (Streptococcus, Neisseria)

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7
Q

What does Factor B or D or properdin deficiency result in?

A

Low C3b levels (no alternative pathway)

Pneumococcal and meningococcal infections

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8
Q

What is the effect of a MAC deficiency?

A

Unable to lyse bacterial cells

Recurrent infection with Neisseria meningitidis

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9
Q

Generally, what do complement deficiencies cause?

A

Increased susceptibility to bacterial infections

Especially Pneumococcus, Streptococcus, Neisseria

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10
Q

What deficiencies in phagocytosis can occur?

A

Problems in stem cell differentiation (neutropenia, leukocyte adhesion disease)

Lack of phagosome and lysosome fusion (Chediak-Higashi syndrome)

Defective intracellular killing (chronic granulomatous disease)

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11
Q

What is the difference between congenital and secondary (extrinsic) phagocytosis deficiencies?

A

Congenital = intrinsic deficiencies in differentiation, chemoattraction, intracellular killing

Secondary = result from deficiencies in another part of the immune system which affect phagocytosis

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12
Q

What conditions involving stem cell differentiation can cause phagocytosis deficiency?

A

Neutropenia

Leukocyte adhesion disease

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13
Q

What is leukocyte adhesion disease?

A

Lack of CD18 on neutrophils which binds to ICAM-1

Essential for recruitment/movement to site

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14
Q

What is Chediak-Higashi syndrome?

A

Lack of fusion of phagosome with lysosomes

Due to defective lysosomal trafficking regulator

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15
Q

What bacteria are those with Chediak-Higashi syndrome particularly susceptible to?

A

Staphylococcus aureus

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16
Q

Describe what causes defective intracellular killing in phagocytosis deficiency.

A

(Chronic granulomatous disease)

Defect in NADPH system (required for ROS formation)

So lack of oxygen-dependent killing

(Increased bacterial and fungal infection)

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17
Q

Generally, what do phagocytosis deficiencies cause?

A

Increased susceptibility to bacterial and fungal infections of skin and mucosal tissues

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18
Q

What is used to treat phagocytosis deficiency?

A

Antibiotics

Bone marrow transplant

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19
Q

What B cell/humoral deficiencies can occur?

A

Abnormal B cell development or lack of Th2 cell activity

B cells failing to develop (Bruton’s agammaglobulinaemia)

Common variable immunodeficiency (IgG and IgA)

No class-switching from IgM (hyper IgM syndrome)

20
Q

What does abnormal B cell development of lack of Th2 cell activity cause?

A

Lack of antibodies

So less/no opsonisation

So defective phagocytosis

21
Q

What is Bruton’s agammaglobulinaemia?

A

X-linked defect in Bruton’s Tyrosine Kinase (BTK)

BTK required for maturation of B cells from pre-B cells

Few/no mature B cells (so no antibodies)

22
Q

Does Bruton’s agammaglobulinaemia occur more frequently in a certain population?

A

Male (infants) as it is X-linked

Protected for 6 months with maternal antibodies then recurrent bacterial infections

23
Q

What is CVID?

A

Common variable immunodeficiency

Cause often unknown

IgG/IgA deficiency

Late onset (15-35yo)

Either no terminal differentiation of B cells of defective T cell signalling

24
Q

What is hyper IgM syndrome?

A

Lots of IgM but little/no IgG in circulation as no class-switching has occurred

So lack of IgG opsonisation and phagocytosis

May be due to defective CD40 (B cell) or CD40L (T cell) affecting costimulatory signalling

25
Q

Generally, what does humoral deficiency cause?

A

Recurrent extracellular bacterial infections (Pneumococcus, Streptococcus, Haemophilus)

Mainly encapsulated organisms

26
Q

How is humoral deficiency treated?

A

Life-long periodic gammaglobulin injections

27
Q

What cellular/T cell deficiencies can occur?

A

Lack of developed thymus (DiGeorge syndrome)

Stem cell defects or death of developing T cells (severe combined immunodeficiency syndrome)

MHC class II deficiency

28
Q

What is DiGeorge syndrome?

A

Lack of developed thymus

So lack of T cells => susceptible to many infections and humoral deficiency

Hypoparathyroidism accompanies = hypocalcaemia

Congenital heart disease accompanies

29
Q

What is SCID?

A

Severe combined immunodeficiency syndrome

Main cause is a defect in γ-chain co-receptor used in cytokine receptors for communication and development

Other causes could be deficiency in adenosine deaminase or purine nucleoside phosphorylase => metabolite build-up which inhibits DNA synthesis in T cells

30
Q

What does MHC class II deficiency cause?

A

No mature CD4+ T cells due to defective APCs during thymus selection

Low aPC function, reduced T and B cell activation, no antibodies

Death by 5yo due to bacterial and viral infections

31
Q

Generally, what do cellular deficiencies cause?

A

Opportunistic infections (also causes humoral deficiencies)

Often fatal in early life

32
Q

How is cellular deficiency treated?

A

Bone marrow transplant

33
Q

What are some clinical features of immunodeficiency?

A

Chronic or recurrent infections

Unusual microbial agents

Incomplete response to treatments

Diarrhoea

Recurrent abscesses

Recurrent osteomyelitis

Autoimmunity

Skin lesions (eg candidiasis, warts)

34
Q

What can cause secondary immunodeficiencies?

A

Therapeutic drugs (chemotherapy, radiotherapy, immunosuppression)

Infection (eg HIV)

Metabolic disorders

Chronic infections (eg diabetes)

Malnutrition

Aging

Burns, trauma (loss of Ig through damaged skin)

35
Q

What does HIV eventually cause?

A

AIDS (acquired immunodeficiency syndrome) => death

36
Q

How many genes does HIV contain and what do they code for?

A

9 genes:

3 core genes for viral components

6 accessory genes that affect host

37
Q

What are the surface proteins on HIV and how many are there?

A

gp120 + gp41 = gp160

~10-30 gp160 per virus

38
Q

What are the general steps of HIV infection?

A
  1. Sequestration/capture by epithelial cells
  2. Langerhan’s cells capture HIV
  3. Transfer of HIV to Th cells/macrophages in submucosa or lymph node
  4. HIV replication
39
Q

Describe the first step of HIV infection (sequestration).

A

gp120 binds and holds HIV at epithelial cells via heparan sulphate proteoglycans (eg syndecans) or galactosylceramide (Galcer)

Waits or gets internalised and integrated into genome (but epithelial cells do not produce new viruses)

40
Q

What surface receptors on Langerhan’s cells help capture HIV?

A

DC-SIGN (binds lectin)

CD4

HSPGs (heparan sulphate proteoglycans)

Galcer (galactosylceramide)

41
Q

What receptors are necessary for HIV to invade Th cells or macrophages?

A

CD4 = main receptor which needs a co-receptor:

  • CXCR4 = Th cells (X4 viruses)
  • CCR5 = macrophages (R5 viruses)
42
Q

Describe how HIV enters Th cells and replicates.

A
  1. Virus binds CD4 and co-receptor (CXCR4)
  2. Viral envelope fuses with cell membrane and viral genome enters cell
  3. Reverse transcriptase copies viral RNA in DS cDNA
  4. Viral cDNA enters nucleus and integrates into host DNA
  5. T cell activation induces low level transcription of provirus (NF-κB)
  6. RNA transcripts are multiply spliced = translation of early genes (tat and rev)
  7. Gag, Pol, Env (late vial proteins) translated and assembled into virus particles which bud from cell
43
Q

What is the function of the Tat gene?

A

Amplifies transcription (of HIV genes)

44
Q

What is the function of the Rev gene?

A

Allows (HIV) RNA to be moved from nucleus to cytoplasm

45
Q

Describe the course of an HIV infection.

A

Initial spike of HIV (viremia) causing flu-like disease = dip in CD4+ T cells (circulating is quickly replenished, mucosal less quickly) = 2-6 weeks

Asymptomatic phase = latency for 5-15 years

Symptomatic phase (viremia) = increase in population of HIV = decrease in CD4+ T cells => AIDS and lots of recurrent infections

46
Q

What concentration of CD4+ T cells in AIDS?

A

< 200/μl

47
Q

What are some signs and symptoms of acute HIV infection?

A

Headache, malaise, fever, nausea, weight loss, myalgia

Sores, thrush orally

Skin rashes

Vomiting

Liver and spleen enlargement

Lymphadenopathy

BDS2 PMI (21 decks)

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