Infection in the Immunocompromised Host Flashcards
What are primary and secondary immunodeficiencies?
Primary - Inherited immunodeficiency
Secondary - can be because of underlying disease state or due to treatment for disease
Why is there an increasingly immunocompromised population?
- Improved survival at extreme ages of life,
- Improved cancer treatment
- Developments in transplant techniques
- Developments in intensive care,
- Management of chronic inflammatory conditions
- Use of steroids
What are the different defects that can arise in the innate immune system
- Colonization resistance (altered microbiome),
- Mucosal barrier injury,
- Organ dysfunction,
- Splenic function,
- Impaired nutritional status,
- Neutropenia/neutrophil function,
- Inherited defects such as chronic granulomatous disease
What are the physical barriers to infections?
- Skin - Desquamates, its dry, has a low pH of 5-6 and IgA is secreted in sweat,
- Conjunctiva,
- Mucous membranes (in gut, respiratory tract and GU tract)
Explain how mucosal barrier injury can effect the immune system
- It can be damaged by chemotherapy or irradiation which can cause mucositis. Mucositis can cause pain, dysphagia, xerostomia and ulceration. This can impair the function og the GI system and lead to altered nutritional status.
Explain how organ dysfunction can affect the immune system
Obstruction of an organ (especially by tumours) can lead to infection, especially in the lung. In the CNS, tumours or spinal cord compression can result in a loss of cough/swallow reflex and cause incomplete bladder emptying which can cause infections
How does stress and diabetes impact immunity?
Stress - reduced T cell function,
Diabetes - reduced opsonization and chemotaxis
Explain how splenic function can impact immunity
- Splenic macrophages eliminate non-opsonized microbes such as encapsulated bacteria.
- The spleen is also the site of primary immunoglobulin response which is required for opsonizing encapsulated bacteria for phagocytosis.
- Hyposplenism can therefore result in S. pneumoniae, haemophilus influenzae type b infections and Neisseria meningitidis
How can an impaired nutritional status impact the immune system?
It can compromise integrity of host defences for example; iron deficiency can reduce microbicidal capacity of neutrophils and T cell function
What is classified as a severe nutritional deficiency?
- Patients who are less than 75% of their ideal body weight, patients with rapid weight loss and hypoalbuminaemia
Describe what can cause neutropenia?
- Cytotoxic drugs/irradiation can result in reduced proliferation of haematopoietic progenitor cells and can cause a depletion of marrow reserves.
- Neutropenia is defined as less than 0.5x10 to the 9/L
What can affect neutrophil function and what does this result in?
- Cytotoxic drugs, irradiation and steroids. This results in less chemotaxis, less phagocytic activity and less intracellular killing. Leaving host susceptible to several bacterial infections
What is chronic granulomatous disease?
An X-linked inherited disease which causes a defect in the gene coding for NADPH oxidase. This results in deficient production of oxygen free radicles and defective intracellular killing.
This can cause recurrent bacterial and fungal infections. The inflammatory responses cause widespread granuloma formation
What are some defects in the adaptive immune system,?
- Humeral immunity,
- Cellular immunity,
- Infections in olid organ transplants
How can defects humeral immunity impact the immune system?
- Antibody production
- Primary defects such as Bruton agammaglobinaemia.
- Lymphoproliferative disorders such as CLL or myeloma which result in reduced antibody productions.
- Intensive radiotherapy and chemotherapy can cause hypogammaglobinaemia.
- At increased risk of capsular organisms
