Immunocompromised Host Flashcards
What is an immunocompromised host?
The state in which the immune system is unable to respond appropriately and effectively to infectious microorganisms – due to a qualitative or quantitative loss
Suggestion of underlying immune deficiency:
- Severe
- Persistent – despite treatment usual treatment
- Unusual (opportunistic infections, odd sites of infection)
- Recurrent
What are some B cell-antibody deficiencies and how may they be managed?
B cell– antibody deficiencies:
Common Variable Immunodeficiency (CVID), IgA deficiency, Bruton’s disease (XLA), IgG subclass deficiency, Hyper-IgM syndrome
o Presentation is with recurrent RTIs, GI complications, arthropathies, increased incidence of lymphoma and gastric carcinoma, barely detectable tonsils/adenoids as they are made of B cells mainly
o Management is with prophylactic antibiotics, immunoglobulin replacement therapy (IRT), avoid radiation exposure, manage respiratory function
What are some disorders of T cell deficiency and how may they be managed?
T cell deficiency:
Di George Syndrome (lack of thymus), Severe Combined Immunodeficiency
o Presentation of SCID: failure to thrive, abscesses, low lymphocyte count, high susceptibility to PCP, VZV< CMV, EBV
o Management of SCID: no live vaccines, irradiated blood products, prevent new infections with isolation and prophylaxis. Long term treatment by bone
marrow/ stem cell transplantation and gene therapy
What are some causes of phagocyte deficiency and how may they be managed?
● Phagocytes- (secondary phagocyte deficiency is more common) – cyclic neutropenia,
leukocyte adhesion deficiency (LAD), chronic granulomatous disease (CDG), Chediak-Higashi Syndrome (defect in phagolysosome formation)
o Presentation is with ulcers, osteomyelitis, deep abscesses, sepsis, invasive aspergillosis, inflammatory problems (granulomas)
o Management is with prophylaxis, surgical management, stem celltransplantation, steroids (CGD)
What are some causes of complement deficiency?
● Complement
– C1 inhibitor deficiency causes hereditary angioedema, immune complex disease (C1,2,4) recurrent infections (C3,5,6,7,8,9)
70% are male because often X linked, it is congenital so often presents in young people but can present at any age
What is secondary immunodeficiency?
Secondary ID – underlying disease or condition affecting immune components due to decreased production or increased breakdown
Why may there be decreased production of immune components?
- Malnutrition
- Infection (HIV)
- Liver diseases
- lymphoproliferative diseases
- Splenectomy
Why is the spleen important in immune defence?
- Immune response against bloodborne pathogens – particularly encapsulated bacteria because they need to be opsonised by spleen (they are very susceptible to neisseria meningitides, haemophilus influenza, streptococcus pneumonia)
- Produces IgM for the initial response and then IgG for long term protection
- Contains lots of macrophages to remove opsonised microbes
Why may there be increased breakdown of immune components?
Increased break down of immune components can be due to:
● Nephropathies that break down proteins
● Enteropathies can cause loss of proteins
● Burns
How may you diagnose an immunodeficiency?
-Full blood count (if all cell counts are low they are pancytopaenic -Test antibody levels -Test lymphocyte subsets (CD4, CD8 etc) -Test phagocytic cells -Test complement -Test molecules and gene mutations to identify specific diseases -Age is important -Take a detailed history
What is Aspergillus?
Aspergillus is an opportunistic mold fungal species which normally resides within dust of buildings which can then be inhaled and cause respiratory tract infections in immunocomprimised people (it doesn’t ‘normally’ cause infections)
What is Varicella Zoster?
Varicella-zoster is a double stranded DNA, enveloped virus that causes chicken pox.
If person has had chickenpox they will normally retain IgG positive for varicella zoster in their blood.
After the initial chickenpox infection is cleared the virus can often remain in the dorsal root ganglia where it remains dormant. Normally, T cells keep it dormant in its latent phase, however, sometimes (more so in immunocomprimised people where they have lower T cell
numbers so can’t keep it in check) the virus can migrate along the sensory nerve and cause an asymmetrical vesicular rash – shingles
In so called ‘normal’ patients treatment is not required but an anti-viral (acyclovir) is required in immunocomprimised people.
What are the virulence factors for staph aureus?
Polysaccharide capsule and protein A that inhibit phagocytosis
Superantigen exotoxins that activate T cells and cause toxic shock syndrome
Toxins cause diarrhoea and skin to peel also
Exotoxins that attack RBC’s
What infections are caused by staph aureus?
The infection produces pus (dead neutrophils accumulations)
Infections caused by staph aureus:
● Pneumonia ● Cellulitis ● Impetigo ● Osteomyelitis ● Lower UTI ● Endocarditis ● Septicaemia ● Gastroenteritis
Where are the different immunoglobulins found? (A, D, E, G, M)
IgA Is not found in blood but in mucous membranes and breast milk to fight bacteria, viruses, fungi and parasites
IgD found on B cells and activate basophils and mast cells
IgE respond to parasitic worms and allergens and activate basophils and mast cells causing secretion of histamines
IgG is the most common immunoglobulin that is found in blood and migrates into tissues as is the smallest. It is involved in a delayed response to an infection activating phagocytes and the complement system but then remains for a long time afterwards and as it is so small is present in the placenta and breast milk to protect the new born.
IgM is the early response before there is enough IgG to counter the attack. They are the largest immunoglobulin.
