4 immunodeficiencies

Question 1

What are immunodeficiency diseases?

Answer 1

A group of diseases where aspects of the immune system are lacking or hyperactive.

Question 2

What are the two broad categories of immunodeficiency?

Answer 2

Primary: Genetic defect in the immune system.
Secondary: Immune system compromised by another condition/factor.

Question 3

What causes primary immune deficiency?

Answer 3

Intrinsic defects in the immune system due to genetic mutations.

Question 4

How are primary immune deficiencies inherited?

Answer 4

Can be dominant or recessive, autosomal or X-linked.

Question 5

Are primary immune deficiencies common?

Answer 5

No, most are rare.

Question 6

What are the major types of primary immune deficiencies?

Answer 6

Complement defects
Phagocytic cell defects
B cell defects (humoral immunity)
T cell defects (cell-mediated immunity)
Combined B and T cell defects

Question 7

What causes secondary immune deficiency?

Answer 7

The immune system is initially intact but compromised by external factors.

Question 8

Examples of causes of secondary immune deficiency?

Answer 8

Malnutrition
Splenectomy
Infections (e.g. HIV)
Medications (e.g. corticosteroids, chemotherapy)
Defects in physical barriers

Question 9

How does secondary immune deficiency affect the immune system?

Answer 9

Impact depends on which part of the immune system is affected and how severely.

Question 10

What are the two main types of immunity affected by immune deficiencies?

Answer 10

Specific (adaptive): T and B cells
Innate: Complement, phagocytes

Question 11

What are the major functions of the immune system?

Answer 11

Defend against pathogens
Regulate inflammation
Tumour surveillance
Maintain self-tolerance

Question 12

What happens when the immune system fails?

Answer 12

Infection: Failure to fight pathogens
Autoimmunity: Attack on self-antigens
Allergy: Response to harmless antigens
Malignancy: Failure of tumour surveillance
Autoinflammation: Dysregulated innate response

Question 13

What are key signs of an immune system error?

Answer 13

Recurrent infections
Opportunistic infections
Increased malignancy risk
Autoimmune disorders
Autoinflammatory conditions

Question 14

When should an immune deficiency be suspected?

Answer 14

Serious, persistent, unusual, or recurrent infections
Family history of immune deficiency
Failure to thrive

Question 15

What is the function of neutrophils?

Answer 15

Engulf and destroy pathogens
Facilitate phagocytosis

Question 16

What pathogens are common in neutrophil defects?

Answer 16

Bacteria: Staphylococcus, Pseudomonas
Fungi: Candida, Aspergillus

Question 17

What is Chronic Granulomatous Disease (CGD)?

Answer 17

A defect in neutrophil oxidative burst, leading to recurrent infections.

Question 18

How is CGD inherited?

Answer 18

X-linked (most common) or autosomal recessive.

Question 19

What are symptoms of CGD?

Answer 19

Recurrent skin abscesses
Lymphadenitis
Pneumonia
Chronic inflammation

Question 20

Causes of secondary neutrophil defects?

Answer 20

Post-infectious neutropenia
Nutritional deficiencies (e.g. folate, B12)
Medications

Question 21

What is the role of antibodies?

Answer 21

Opsonization
Neutralisation
Complement activation

Question 22

What infections are common in B cell defects?

Answer 22

Bacterial: Encapsulated bacteria (Streptococcus pneumoniae, H. influenzae)
Viral: Enteroviruses
Protozoal: Giardia

Question 23

What is X-linked agammaglobulinaemia (XLA)?

Answer 23

A condition with very low or absent B cells and immunoglobulins.

Question 24

Why do XLA symptoms start at 6-12 months?

Answer 24

Maternal antibodies provide initial protection.

Question 25

Symptoms of XLA?

Answer 25

Recurrent respiratory infections Sepsis, meningitis, osteomyelitis

Question 26

Secondary causes of humoral immune deficiency?

Answer 26

Medications (e.g. rituximab, chemotherapy) Protein loss (e.g. nephrotic syndrome)

Question 27

What is the role of complement?

Answer 27

Opsonization Immune complex clearance Direct lysis of bacteria

Question 28

What infections are common in complement deficiency?

Answer 28

C3 deficiency: Pneumococcal, H. influenzae infections C5-C9 deficiency: Neisserial infections

Question 29

What autoimmune disease is associated with complement deficiency?

Answer 29

Systemic Lupus Erythematosus (SLE).

Question 30

What drug can cause secondary complement deficiency?

Answer 30

Eculizumab (C5 inhibitor).

Question 31

Why do T cell defects also affect B cells?

Answer 31

Most B cell antibody production requires T cell help.

Question 32

What infections are common in T cell deficiency?

Answer 32

Viral: CMV, RSV Fungal: Pneumocystis jirovecii Protozoal: Cryptosporidia, Toxoplasma

Question 33

What is Severe Combined Immunodeficiency (SCID)?

Answer 33

A fatal disorder with combined T and B cell failure.

Question 34

When should SCID be suspected?

Answer 34

Persistent lymphopenia (<2 × 10⁹/L), especially in infants <6 months.

Question 35

Symptoms of SCID?

Answer 35

Failure to thrive Chronic diarrhoea Persistent viral infections

Question 36

Treatment for SCID?

Answer 36

Haematopoietic stem cell transplantation (HSCT) Gene therapy for some forms

Question 37

Causes of secondary T cell deficiency?

Answer 37

HIV Immunosuppressive drugs (e.g. calcineurin inhibitors, anti-TNF therapy)

Question 38

What is used to treat antibody deficiencies?

Answer 38

Immunoglobulin replacement therapy.

Question 39

What is the function of monoclonal antibodies (MoAbs)?

Answer 39

Depleting (e.g. anti-CD3) Non-depleting (blocking function)

Question 40

Is primary or secondary immune deficiency more common?

Answer 40

Secondary immune deficiency is more common.

Question 41

Do primary immune deficiencies only affect infections?

Answer 41

No, they can also cause autoimmunity, allergy, and malignancy.

Question 42

Which therapy expands immune deficiency risk?

Answer 42

Biological immunotherapies (e.g. CAR-T cells).

Question 43

What therapy can be curative for some primary immunodeficiencies?

Answer 43

Haematopoietic stem cell transplantation (HSCT).

Question 44

What increases the risk of inherited immune disorders?

Answer 44

Consanguinity (related parents).

Question 45

What is the best approach to prevent infections in immunodeficient patients?

Answer 45

Prophylactic antibiotics, antifungals, and immunoglobulin therapy.

Question 46

Which infection is common in complement deficiency?

Answer 46

Neisseria meningitidis.

Question 47

What condition is linked to antibody loss in nephrotic syndrome?

Answer 47

Hypogammaglobulinaemia.

Question 48

Why must SCID patients avoid live vaccines?

Answer 48

Risk of severe or fatal infection.