Immunology 2: Primary Immunodeficiency

Question 1

Which antibody is maternally transferred?

Answer 1

IgG

Question 2

What is the difference between primary and secondary immunodeficiency?

Answer 2

• Primary: are congenital

- Secondary: are acquired

Question 3

Which parts of the immune system can be abnormal in primary immunodeficiency?

Answer 3

• The Innate immune system
• Stages of lymphocyte development
• Responses of mature lymphocytes to antigenic stimulation

Question 4

What happens when there is a mutation or defect in the process that creates lymphocytes?

Answer 4

There will be a lack of normal function in the T or B lymphocytes

Question 5

What are the features of B cell deficiency?

Answer 5

• Susceptibility to infection (pyogenic bacteria e.g. pneumonia, meningitis etc.)
• Reduced serum antibody levels
• Absent or reduced follicles and germinal centres in the lymph nodes
• Normal DTH reactions to common antigens

Question 6

What are the features of T cell deficiency?

Answer 6

• Susceptibility to infection (pneumocytis jiroveci, viruses, atypical mycobacteria and fungi)
• Normal or reduced serum antibody levels
• Reduced DTH reactions to common antigens
• Reduced parafollicular cortical regions of the lymph nodes

Question 7

What does a repeated infection with encapsulated bacteria suggest?

Answer 7

Defective antibody production

Question 8

What does recurrent respiratory infection by pneumococcus or haemophilus spp. suggest?

Answer 8

Antibody deficiency (IgG and IgA)

Question 9

What are infections with staph, gram-negative bacteria and fungi associated with?

Answer 9

Reduced number or function of phagocytes

Question 10

What does meningitis caused by Neisseria suggest?

Answer 10

Defects in the complement cascade

Question 11

What are infections with intracellular organisms (protozoa, viruses and intracellular bacteria including mycobacteria) associated with?

Answer 11

Defects in T cells or macrophages

Question 12

How do mycobacterial infections differ in T cell immunodeficiency?

Answer 12

• Increased severity

- Predisposition to widespread infection

Question 13

What is reactivation of latent herpes virus infection associated with?

Answer 13

T cell immunodeficiency

Question 14

What are recurrent attacks of cold sores or shingles associated with?

Answer 14

Mild immunodeficiency

Question 15

What are recurrent candida infections associated with?

Answer 15

Defects in the Th17 pathway

Question 16

What are herpesvirus induced tumours: Kaposi sarcoma and non-Hodgkin lymphomas characteristic of?

Answer 16

T cell dysfunction

Question 17

What is a mutation?

Answer 17

A permanent alteration in the DNA sequence that makes up a gene

Question 18

What is a polymorphism?

Answer 18

One or more variants of a particular DNA sequence (the most common involve a single base pair)

Question 19

What are polygenic disorders?

Answer 19

Disorders caused by the combined action of more than one gene (polygenic disorders of the immune system affect mainly antibodies)

Question 20

What is SCID?

Answer 20

Severe combined immunodeficiency

Question 21

Name two alleles which the absence of can increase the risk of infection

Answer 21

• HLA

- Mannan-binding lectin

Question 22

What are the features of common variable immunodeficiency?

Answer 22

• Patients have low levels of total IgG, IgA and IgM
• The numbers of B and T cells are variable
• Causes recurrent respiratory tract infections
• Infections involving the gut, skin and nervous system can also occur
• Autoimmunity is common
• Autosomal recessive inheritance

Question 23

How does severe combined immunodeficiency present?

Answer 23

• Infections within the first few weeks
• Unusual or recurrent infection
• Diarrhoea
• Unusual rashes
• FH of neonatal death or consanguinity
• Very low lymphocyte count (should be measured by flow cytometry)

Question 24

How can primary immunodeficiency be treated?

Answer 24

• Prophylactic antibiotics for mild immunodeficiency

- Immunoglobulin replacement therapy for more severe antibody deficiency

Question 25

In SCID, what should be done until definitive treatment is given?

Answer 25

• Avoid live vaccines (MMR and polio etc.)

- Prophylaxis against opportunistic infections e.g. Pneumocystis jiroveci

Question 26

What treatment is needed in most T cell deficiencies and SCID?

Answer 26

• Stem cell transplantation (most effective within a few weeks of birth)
• Gene therapy can also be used