16. Immunocompromised Host Flashcards
What is an immunocompromised host?
State in which the immune system is unable to respond appropriately and effectively to infectious microorganisms
Due to a defect in one or more components of the immune system
Why can a host be immunocompromised?
Primary immunodeficiency (congenital) - due to intrinsic gene defect: missing protein, missing cell, non-functional components
Secondary immunodeficiency (acquired) - due to underlying disease/treatment: decreased production/function of immune components, increased loss of catabolism of immune components
What can cause secondary immunodeficiency?
HIV Chemotherapy Cancer Infections Immunosuppressants (steroids)
When do you suspect an immunodeficiency?
Infections defined as SPUR
Severe - IV antibiotics, hospitalisation
Persistent - despite conventional treatment not responding, or takes longer than usual
Unusual - site of infection, type of microorganism
Recurrent
What are the broad categories of immunodeficiencies caused by antibody defects?
Defect in B cell development
Defect in antibody production
What are the defects in B cell development?
X-linked agammaglobulinaemia (Bruton’s disease)
- cannot produce antibodies
What are the defects in antibody production?
Common variable immunodeficiency Selective IgA deficiency IgG subclass deficiency Hyper-IgM syndrome - unable to produce IgG
What is the most common defect in antibody production that requires treatment?
Common variable immunodeficiency
What is the most common defect in antibody production but is asymptomatic?
Selective IgA deficiency
What can happen if immunoglobulin replacement therapy is given to someone with selective IgA deficiency?
Patients with this immunodeficiency may develop anti-IgA antibodies so the body rejects the immunoglobulin replacement therapy and has an anaphylactic shock
What are the broad types of immunodeficiency caused by T cell defects?
Combined B and T cell defects
T cell defects
What are the types of combined B and T cell defects?
Severe combined immunodeficiency (SCID)
Wiskott-Aldrich syndrome
Ataxia telangectasia
What are the T cell defects?
Di George syndrome (thymus) - either no thymus or missing part of thymus so T cells cannot mature CD3 deficiency MHC class II deficiencies MHC class I deficiency
What are the broad types of immunodeficiencies causes by phagocytic defects?
Defects in respiratory burst
Defect in fusion of lysosome/phagosome
Defect in neutrophil production and chemotaxis
What is the defect in respiratory burst?
Chronic granulomatous disease (CGD)
Wha is the defect in fusion of lysosome/phagosome?
Chediak-Higashi syndrome
What are the defects in neutrophil production and chemotaxis?
Cyclic neutropenia
LAD protein deficiencies
What is the most common cause of secondary immunodeficiency?
Malnutrition
What are the most likely primary immunodeficiency diseases if symptom onset is <6 months?
T cell or phagocyte defect
What are the most likely primary immunodeficiency diseases if symptom onset is >6 months and <5 years old?
B cell antibody or phagocyte defect
What are the likely primary immunodeficiency diseases if symptom onset is >5 years old?
B cell/antibody/complement or secondary immunodeficiency
What are the most common bacteria in complement deficiency?
Neisseria, streptococci
Which immune defect is giardia lamblia most commonly seen in?
Antibody deficiency
What is the supportive treatment for PIDs?
Infection prevention (prophylactic antimicrobial)
Treat infections promptly and aggressively
Nutritional support
Use UV-irradiated CMVneg blood products only
Avoid live attenuated vaccines
What is the specific treatment of PIDs?
Regular immunoglobulin therapy
SCID: haematopoietic stem cell therapy
What is the goal of immunoglobulin replacement therapy?
Serum IgG>8g/l
Life long treatment
What conditions is immunoglobulin replacement therapy used in?
CVID
XLA (Bruton’s disease)
Hyper-IgM syndrome
What are the secondary immune deficiencies caused by?
Decreased production of immune components
Increased loss of immune components
What can cause decreased production of immune components?
Malnutrition Infection Liver diseases Haematological malignancies Therapeutic treatment Splenectomy
What can cause increased loss of immune components?
Protein-losing conditions (nephropathy, enteropathy)
Burns
