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Y2 Clinical Pathology > Immunodeficiency > Flashcards

Immunodeficiency Flashcards

1
Q

The main physiological function of the immune system is to protect from infection.

What does it need to do in order to be able to do this?

A
  • Recognise pathogens
  • mount an immune response which requires cell-to-cell communication
  • clear the pathogen
  • self-regulation
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2
Q

What may clearing tha pathogen require?

Why is self-regulation important?

A

Clearing the pathogen may require adaptive responses to the changing pathogen

Self-regulation is important to minimise host damage

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3
Q

What are the characteristics of innate immunity?

A
  • General - it is NOT antigen-specific, but can recognise broad classes
  • rapid speed of onset
  • does not alter on repeated exposure (same response happens each time)
  • no memory
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4
Q

What are the characteristics of adaptive immunity?

A
  • Antigen specific
  • slower response, but it is more potent due to antibody production
  • subsequent exposure leads to a more effective response
  • memory
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5
Q

Complete the diagram showing the innate and adaptive immune responses

A
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6
Q

What is meant by immunodeficiency?

A

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

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7
Q

What are the 2 different types of immunodeficiency?

A

Primary:

  • there is an inherent defect within the immune system
  • this is usually genetic

Secondary:

  • the immune system is affected due to external causes
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8
Q

What are the secondary causes of immunodeficiency?

A
  1. Breakdown in physical barriers - e.g. cystic fibrosis
  2. Protein loss
  3. Malignancy
  4. Drugs
  5. Infection
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9
Q

How can cystic fibrosis act as a secondary cause of immunodeficiency?

A

Mucus mounts up as it cannot be cleared

pathogens will collect within this mucus, and are more likely to cause infection

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10
Q

How can protein loss and malignancy act as a secondary cause of immunodeficiency?

A

Protein loss:

  • burns
  • protein loosing enteropathy
  • malnutrition
  • this can lead to the loss of immunoglobulins

Malignancy:

  • in blood cancers, the clones of the cells expand in the immune system and take up space
  • e.g. Lymphoproliferative disease, myeloma
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11
Q

Which drugs and infections act as secondary causes of immunodeficiency?

A

Drugs:

  • steroids
  • DMARDS
  • Rituximab
  • anti-convultants
  • myelosuppressive drugs that knock out the bone marrow

Infection:

  • HIV
  • TB
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12
Q

What are the 2 main types of phagocytes?

What is their role?

A

Neutrophils are short-lived

macrophages are long-lived and found in tissues

they ingest bacteria and fungi and then destroy them

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13
Q

What is a pathogen recognition receptor?

A

PRRs recognise conserved pathogen associated molecular patterns (PAMPs)

These are unique to each pathogen

They tend to be repeated sequences, such as lipopolysaccharides on bacteria

Phagocytes use PRRs to detect pathogens and ingest them

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14
Q

What are the 3 main toll like receptors?

A

Toll like receptors are a type of PRR

  • TLR4 recognises lipopolysaccharide
  • TLR5 recognises flagellin (found on some bacteria)
  • TLR3 recognises viral RNA within the nucleus
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15
Q

What happens if there is a defect in TLR3?

A

Without TLR3, the cell does not recognise viruses

This leads to recurrent HSV encephalitis (herpes simplex virus)

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16
Q

What happens when the toll like receptor binds to the molecule that it recognises?

A

It leads to a cascade of events involving various intracellular molecules

this leads to the production of inflammatory cytokines

MyD88 and IRAK4 are involved in this cascade

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17
Q

If a patient had IRAK4 or MyD88 deficiency, what would the clinical presentation be like?

A
  • Recurrent bacterial infection - especially streptococcus and staphylococcus

This includes pneumonia, meningitis, arthritis

  • poor inflammatory response
  • susceptibility to infection decreases with age
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18
Q

What is meant by a “poor inflammatory response” in IRAK4 deficiency?

A

The patient will NOT have raised CRP and they will have normal levels of lymphocytes and neutrophils

This is because cytokines are not being released, so the patient feels okay

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19
Q

What is the treatment for IRAK4 of MyD88 deficiency?

A
  1. Prophylactic antibiotics
  2. IV immunoglobulin if severe
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20
Q

What is the role of the phagolysosome?

How is the NADPH complex involved?

A

The NADPH complex is formed of several proteins, including gp91phox

This is encoded by the X chromosome

NADPH releases an electron, which combines with superoxide to produce hypochlorous acid

This is a bleach that will kill the pathogen

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21
Q

How does chronic granulomatous disease present?

A
  • Recurrent abscesses - in the lung, liver, bone, skin and gut
  • inflamed lymph nodes
  • infection with unusual organisms - staphylococcus, klebsiella, serretia, aspergillus
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22
Q

What would you see in a clinical presentation of a patient with chronic granulomatous disease?

A
  • History of recurrent skin abscesses
  • maybe previous pneumoia
  • normal immunoglobulins, lymphocytes and neutrophil count
  • it is an X-linked recessive disease, so may be family history
23
Q

What is the background behind chronic granulomatous disease?

A

There is a mutation in gp91phox, meaning the NADPH complex does not work

This means that no hypochlorous acid is produced within the phagolysosome

Neutrophils can’t kill bacteria, but they can take them up

24
Q

What is the treatment for chronic granulomatous disease?

A
  • Haemopoeitic stem cell transplant
  • antibiotics
25
Q

How can you test to see if someone has chronic granulomatous disease?

What does the test rely on?

A

Test the function of macrophages by measuring dihydrorhodamine reduction using flow cytometry

This test relies on REDUCTION

DHR in the blood is reduced by the e- released from NADPH, causing activation of the neutrophil by PMA

26
Q

What visual test can be used for chronic granulomatous disease?

A

Nitro blue tetrazolium dye reduction

in this test, healthy neutrophils should turn purple in colour

27
Q

What is meant by “complement”?

What are their roles?

A

Non-immunoglobulin proteins, that are important in the immune system for:

  1. Cell lysis
  2. Control of inflammation
  3. Stimulation of phagocytosis
28
Q

How can you test complement function?

A

Complement should lose foreign cells if the foreign cells are covered in antibody

this will trigger the classical complement cascade

patients serum is placed on sheep erythrocytes, and it should lyse them

29
Q

What are the 2 types of complement deficiency and how do they tend to present?

A

C2, C4 deficiency:

  • presents as SLE, infections and myositis

C5 - C9 deficiency:

  • these form the membrane attack complex
  • presents with repeated episodes of BACTERIAL MENINGITIS
  • particularly with infection with Neisseria meningitis
30
Q

How does the adaptive immune system work?

A

The antigen binds to the B cell (antigen-presenting cell)

The B cell presents the antigen to the helper T cell via MHCII

The T cell stimulates the B cell to proliferate and differentiate

The plasma cells are stimulated to produce antibodies

31
Q

What are the roles of T helper cells (CD4)?

In which disease are they compromised?

A

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

In HIV, there is a low CD4 count

32
Q

What is the role of the plasma cell?

A

They stay in the blood for a long period of time and produce the same antibody

33
Q

Complete the table showing the roles of antibodies binding to antigens

A
34
Q

What causes X-linked agammaglobulinaemia?

A

NO antibodies are produced

This is due to a defect in Bruton’s tyrosine kinase (BTK)

this is needed for B cell signalling and B cell maturation

B cell maturation is not completed in the bone marrow so no antibodies are produced

35
Q

What are the typical presentations of X-linked agammaglobulinaemia?

A

Patients present young (before age 5)

Previous hospital admissions with pneumonia and recurrent chest infections

Relatives may have passed away young from bronchiectasis (scarring of the lungs that builds up with each infection)

36
Q

What would the bloods look like in someone with X-linked agammaglobulinaemia?

A
  • No B cells but normal T cells
  • No IgG, IgA or IgM
  • CT shows bronchial thickening
37
Q

How does the defect in BTK affect B cell production?

A

The defect means that B cells are not present in the periphery

Plasma cells are not produced, so there are no antibodies

38
Q

What are 4 other B cell defects?

A
  • CVID
  • IgA deficiency
  • X linked hyper IgM syndrome
  • transient hypogammaglobulinaemia of infancy
39
Q

What are patients with IgA deficiency more prone to?

A

They have no IgA antibodies

Most patients are fine, some have recurrent infections

They are more prone to autoimmune diseases

40
Q

What is meant by transient hypogammaglobulinaemia of infancy?

A

A patient has no antibodies when they are a baby, but acquires them when they get older

A baby does not start making antibodies until around 4-5 months of age

(they initially have antibodies from their mother)

41
Q

What are the consequences of a B cell defect?

What is the treatment?

A
  • Loss of antibody secretion
  • usually leads to recurrent bacterial infection with pyogenic organisms
  • treat with antibiotics and then IV IgG for life
42
Q

What is a more common reason to have an antibody deficiency?

A

Secondary antibody deficiency due to drugs

often caused by immunosuppressants such as:

  1. Methotrexate
  2. Infliximab
  3. Rituximab
43
Q

What would the bloods look like in a patient with secondary antibody deficiency due to drugs?

A
  • Slightly low B and T cells
  • low IgG and IgA
44
Q

Why does someone acquire a secondary antibody deficiency due to drugs?

A

Drugs (such as Rituximab) target the CD20 molecule on the surface of B cells

This prevents the B cell from functioning, differentiating and producing antibodies

45
Q

What are the main mechanisms of antibody deficiency treatment?

A
  • Antibiotics
  • immunoglobulin G replacement
46
Q

How would chickenpox vary in a healthy child and a child with SCID?

A

Healthy:

  • mild disease with typical vesicles

SCID:

  • fulminant disease with haemorrhagic lesions
  • may have pneumonitis and/or meningitis
47
Q
A
48
Q

What would the blood results look like in a young child presenting with severe combined immunodeficiency (SCID)?

A
  • Normal levels of IgG (as this comes from the mother for the first 6 months of life)
  • no IgA
  • reduced IgM
  • lymphocyte markers show absent/reduced T cells and NK cells but present B cells
49
Q

Why are defects in T cells usually more severe than defects in B cells?

A

B cells also need T cell help

Even if there are B cells, they will not function

50
Q

WHat are the symptoms of a T cell defect (SCID or DOCK8 deficiency)?

A
  • Recurrent infection with opportunistic pathogens
  • These are infections that a healthy person wouldn’t usually contract
  • e.g. Candida (fungi) or pneumocystis (protozoa)
51
Q

what are the treatments for SCID?

A
  • Antibiotics, antivirals and antifungals
  • asepsis
  • haemopoietic stem cell transplant is the only cure (i.e. bone marrow transplant)
52
Q

What are the causes of SCID?

A

Defect/absence of a critical T cell molecule:

  • T cell receptor, common gamma chain
  • if any of the chains are missing, the TCR will not function

Loss of communication:

  • deficiency of MHCII means there is no communication between B and T cells

Metabolic:

  • adenosine deaminase deficiency
  • leads to a build up of metabolites that are toxic to lymphocytes
53
Q
A

Y2 Clinical Pathology (76 decks)

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