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Clinical Pathology > Theme 2 Lecture 9: Immunodeficiency > Flashcards

Theme 2 Lecture 9: Immunodeficiency Flashcards

1
Q

Give 4 features of innate immunity

A
  • general, not antigen specific, but can recognise broad classes e.g bacteria
  • rapid speed of onset
  • does not alter on repeated exposure
  • no memory
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2
Q

Give 4 features of adaptive immunity

A
  • antigen specific
  • slower response, but more potent
  • subsequent exposure - more effective response
  • memory
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3
Q

What is immunodeficiency?

A

Clinical situations where the immune system is not effective enough to protect the body against infection

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4
Q

What is primary immunodeficiency?

A

inherent defect within the immune system - usually genetic

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5
Q

What is secondary immunodeficiency?

A

immune system affected due to external causes

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6
Q

What are 5 causes of secondary immunodeficiency?

A
  1. breakdown in physical barriers e.g in CF, there is a compromised mucosal barrier in the lung leading to recurrent infections
  2. protein loss e.g burns, malnutrition
  3. malignancy
  4. drugs - that suppress the immune system e.g for autoimmune conditions
  5. infection - HIV, TB
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7
Q

What are the two types of phagocytes?

A

neutrophils and macrophages

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8
Q

What is the difference between neutrophils and macrophages?

A
  • neutrophils are short lived, blood residents and can migrate when needed
  • macrophages are tissue residents
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9
Q

What do PRRs do?

A
  • pathogen recognition receptors
  • recognise conserved pathogen associated molecular patterns (PAMPs)
  • phagocytes use PRRs to detect pathogens
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10
Q

What is an example of PAMP?

A

Lipopolysaccharide

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11
Q

What effect might an IRAK4 or MyD88 deficiency have?

A
  • recurrent bacterial infection, pneumonia, meningitis, arthritis
  • poor inflammatory response
  • susceptibility to infection decreases with age
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12
Q

How does a phagolysosome kill bacteria?

A
  • NADPH complex - formed of several proteins including gp91phox
  • electron binds to oxygen producing superoxide
  • then becomes hypochlorous acid
  • hypochlorous acid is essentially bleach that kills fungi and bacteria
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13
Q

What is a granuloma?

A

collection of macrophages

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14
Q

Explain the genetic cause of chronic granulomatous disease

A
  • CGD is where there is an abnormality of gp91phox

- affects X chromosome so seen in males

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15
Q

What is the presentation of CGD?

A
  • Recurrent abscesses: lung, liver, bone, skin, gut

- unusual organisms e.g staphylococcus, klebsiella, aspergillus

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16
Q

what is the treatment for CGD?

A
  • Treatment: haemopoietic stem cell transplant, antibiotics

- patients typically need bone marrow transplant as they are prone to infection

17
Q

How do we test for CGD?

A
  • Neutrophil function test
  • tests rely on reduction (gain of electron)
  • measure dihydrorhodamine reduction (can be picked up on in neutrophils) using flow cytometry
  • in patients with CGD, patients were unable to reduce DHR
18
Q

Other than the neutrophil function test, how else can we diagnose CGD?

A

Nitro blue tetrazolium dye reduction

-healthy neutrophils should turn purple

19
Q

What are complement proteins important in the immune system for?

A
  • cell lysis (kill invading bacterium)
  • control of inflammation
  • stimulate phagocytosis
20
Q

What are the 3 complement pathways called?

A

classic, alternative and MBL

21
Q

what is the last event in the complement pathway?

A

Forming MAC complex, which lysis bacteria surfaces

22
Q

What is the function of complement?

A
  • should lyse foreign cells if the foreign cells are covered in antibody
  • will trigger the classical complement cascade
23
Q

A deficiency in which complement proteins might predispose to SLE, Infections and myositis?

A

C2, C4 (complements in the early classical pathway)

24
Q

A deficiency in which complement proteins presents with repeated episodes of bacterial meningitis?

A

C5-C9 (form membrane attack complex)

25
Q

What do T helper cells do?

A

produce cytokines that effect B cells and the recruitment of other immune cells

26
Q

Explain briefly how adaptive immunity works

A
  • antigen binds to B cell and presents on an MHC II molecule to a Th cell
  • Th produce cytokines that stimulate B cells, so the B cells differentiate into memory and plasma cells which make antibodies
27
Q

How does binding of antibodies to antigens inactivate the antigen?

A
  • neutralisation (blocks viral binding sites; coats bacteria)
  • agglutination of microbes
  • precipitation of dissolved antigens
  • all of above enhances phagocytosis
  • activation of complement system —> cell lysis
28
Q

What is X linked agammaglobulinaemia?

A
  • defect in Bruton’s tyrosine kinase
  • this is needed for B cell signalling and B cell maturation
  • B cell maturation not completed in the bone marrow
  • antibodies not produced
  • occurs almost exclusively in males
29
Q

Name 4 other B cell defects, other than X linked agammaglobulinaemia

A
  • Common Variable Immune Deficiency (CVID)
  • IgA deficiency (most common antibody deficiency)
  • X linked hyper IgM syndrome
  • transient hypogammaglobulinaemia of infancy
30
Q

Which drugs could potentially cause secondary antibody deficinecy?

A

rituximab, methotrexate

31
Q

How do we treat antibody deficiency?

A
  • antibiotics
  • immunoglobulin G replacement
  • IgG is most potent antibody and useful in clearing infection
32
Q

What is SCID?

A
  • Severe combined immunodeficiency
  • reduced T and NK cells
  • without T cells you don’t get a sufficient B cell response either
33
Q

How do we treat SCID?

A

-paediatric emergency, antibiotics, antivirals, antifungals, asepsis, haemopoietic stem cell transplant (only cure)

34
Q

What are the causes of SCID?

A
  • defect / absence of T cell
  • loss of communication - MHC II deficiency
  • metabolic - adenosine deaminase deficiency
35
Q

Summarise the main potential immunodeficiencies

A

phagocyte:

  • PRR: IRAK4 –> recurrent pneumonia, poor inflammatory response
  • CGD
  • Complement - bacterial meningitis
  • antibodies - X linked agammaglobulinaemia
  • T cells - SCID

Clinical Pathology (57 decks)

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