Infection 17 - The Immunocompromised Host

Question 1

What is the difference between primary (congenital) immunodeficiency and secondary (acquired) immunity?

Answer 1

Primary = due to intrinsic gene defect (e.g.: missing protein, non-functional components)

Secondary = due to underlying disease/treatment (e.g.: HIV/chemotherapy)

Question 2

What is immunodeficiency caused by?

How do we suspect an immunodeficiency?

Answer 2

• A defect in one or more components of the immune system

- SPUR - severe, persistent, unusual and recurrent infections.

Question 3

65% of immunodeficiencies are caused by antibody defects. Give examples of PID’s caused by defects in:

1) B-cell development
2) Antibody production

Which disease is the most common?

Answer 3

1) X-linked agammaglobulinaemia (Bruton’s disease) - no B-cells so no antibodies produced at all
2) Common Variable Immunodeficiency (CVI) - have B-cells but dont produce antibodies

Selective IgA deficiency - No IgA

NB: CVI is the most common antibody defect requiring treatment. IgA is the most prevalent but a-lot of patients are asymptomatic.

Question 4

15% of immunodeficiencies are caused by T-cell defects. Give examples of PID’s caused by:

1) Combined B+T cell deficiencies
2) T-cell defects

Answer 4

1) Severe combined immunodeficiency (SCID) - T-cells defective, no B-cell activation
2) Di George syndrome (patient w/no thymus) - T-cells can’t mature

Question 5

10% of immunodeficiencies are caused by phagocytic defects. Give examples of PIDS caused by defects in:

1) Respiratory burst
2) Fusion of lysosomes/phagosomes

Answer 5

1) Chronic granulomatous disease (CGD) - no oxygen dependent mechanism to kill bacteria/pathogen within phagocyte.
2) Defect in fusion of lysosome/phagosome

Question 6

What does the age of symptom onset for PID’s suggest for the following:

1) <6 months
2) Between 6 months and 5 years
3) Over 5 years old

Answer 6

1) T-cell or phagocyte defect. Most likely NOT antibody problem as they are still protected by maternal antibodies.
2) B-cell antibody or phagocyte defect
3) B-cell/antibody/compliment defect or SID (secondary)

Question 7

What are the supportive + specific treatments for PID’s?

Answer 7

Supportive =

• Infection prevention (prophylaxis)
• Treat infections quickly + aggressively
• Nutritional support
• Avoid live attenuated vaccines

Specific =

• Regular immunoglobulin therapy (IVIG or SCIG)
• Haematopoetic stem cell therapy for SCID