ALLERGY & IMMUNOLOGY Flashcards
What are the 4 major categories of immunodeficiencies?
- Defective cell-mediated immunity
- Defective antibody-mediated immunity
- Defective phagocytosis
- Defective complement function
What are the infection susceptibilities with the following immunodeficiencies? What is your test for diagnosis?
- humoral (antibody mediated)
- cell mediated
- phagocytes
- complement
- Humoral:
- deficiency in antibodies = infections start after 6 months when maternal antibodies start to wane
- infections with encapsulated bacteria
- test: immunoglobulin levels, immune titres (antibody response to vaccines) - Cell mediated: difficulty with bacteria
- fungal infections (especially aspergillus and candida)
- unusually severe viral infections
- pneumocystis, mycobacteria
- test: lymphocyte count, T cell subsets (CD4, CD8) - Phagocytes:
- CATALASE POSITIVE organisms (staph, nocardia, serratia, aspergillus, salmonella)
- abscesses, skin infection
- poor wound healing
- test: CBC + diff, looking at WBC differential - Complement:
- neisseria meningitidis and neisseria gonorrhea
- sepsis with encapsulated bacteria
- test: CH50 (total hemolytic component)
Which class of immunodeficiency is the most common primary immunodeficiency?
Antibody-mediated immunodeficiency (B-cell) - up to 50% of primary immunodeficiencies in kids
What are 2 potential complications of long-term IVIG treatment?
- Chronic lung disease (need PFTs q1yr)
2. Exposure to bloodborne pathogens
What is the pathogenesis of Bruton’s agammaglobulinemia?
- pattern of inheritance?
- at risk for which organisms?
- clinical features?
- diagnosis?
- treatment? (3)
Pathogenesis: defective B cell production due to enzyme deficiency (tyrosine kinase)–> NO B CELLS = no antibodies (agammaglobulinemia)
- X-linked = only affects males
- at risk for: staph aureus, strep pneumo, H flu, pseudomonas, giardia, enterovirus
Clinical features:
- No lymphoid tissue! = small or absent tonsils & no palpable lymph nodes (that’s because you need B cells to have lymph tissue)
- Pyogenic bacterial infections of the resp tract, skin and joints (sinusitis, pneumonia, meningitis, etc.)
- Enterovirus infections are severe and can be fatal
- Risk of life threatening pseudomonas infections
Diagnosis:
- Immunoglobulin levels: will see low levels or completely absent
- Bone marrow with absence of B cells on flow cytometry
Treatment:
- IVIG replacement monthly
- Avoidance of live virus vaccines
- Follow PFTs and CT chests since patients are prone to develop bronchiectasis
What 5 organisms are most common causes of infection for patients with antibody-mediated (B cell) immunodeficiency?
- Staph aureus
- Strep pneumo
- H. flu
- Pseudomonas
- Giardia
What is the pathogenesis of common variable immunodeficiency (CVID)?
- clinical features? (3)
- pattern of inheritance?
- treatment? (3)
Hypogammaglobulinemia with phenotypically NORMAL B cells that fail to mature appropriately into antibody-producing plasma cells
-no clear pattern of inheritance
Clinical features:
- recurrent bacterial infections (sinopulmonary, mycoplasma) and viral infections (enteroviruses) and parasitic infections (giardia)
- Autoimmune manifestations: inflammatory bowel disease like picture: diarrhea, weight loss, malabsorption, cytopenias
- Increased risk of malignancy: lymphoma and other malignancies
Treatment:
- IVIG replacement
- May require immunosuppressive treatment for rheumatologic disorders
- Monitor for malignancy!!
How do you differentiate between Bruton’s agammaglobulinemia and CVID?
Given that they are both disorders of absent antibody production, will have similar infection susceptibilities. Thus, can differentiate by:
- Agammaglobulinemia: see only in males (X-linked), NO lymphoid tissue, NO B cells on bone marrow, see more enterovirus infection than with CVID
- CVID: see in both males and females, normal lymphoid tissue, normal B cells on bone marrow
What conditions are patients with CVID at increased risk for? (3)
- Lymphoma
- Autoimmune disorders
- Noncaseating granulomas of spleen, liver, lungs and skin
What is the most common immunodeficiency syndrome?
IgA deficiency
Which infections are patients with IgA deficiency at most risk, in general terms? (3)
IgA protects mucosal surfaces THUS are most susceptible to bacterial and viral infections involving mucosal surfaces such as:
- Respiratory tract
- Urinary tract
- GI tract
A patient receiving a blood transfusion post-trauma develops anaphylaxis. You have double-checked the blood product and it is correctly cross-matched to the patient. What diagnosis should you rule out?
Undiagnosed IgA deficiency = trace amounts of IgA in a blood product may trigger anaphylaxis in a patient who does not have IgA!
What is the diagnosis and treatment of IgA deficiency?
-minimum age at which IgA deficiency can be diagnosed?
Diagnosis: serum IgA levels < 10 mg/dL
- cannot confirm diagnosis until at least 4 yo when IgA levels should reach adult levels
- treatment: targeted treatment of associated infections (IVIG is not indicated since these patients make IgG normally)
What is the pathogenesis of IgG subclass deficiency? -at risk for what type of infections?
Occurs when the level of abs in one or more IgG subclasses (IgG1-4) is selectively decreased while total IgG levels are normal
-recurrent upper resp tract infections
What is the pathogenesis of Hyper IgM syndrome?
-inheritance pattern of most common form of Hyper IgM?
Failure of immunoglobulin isotype switching from IgM to IgG, IgA or IgE.
- most commonly X-linked: defect in CD40 ligand gene thus, the T cell with CD40 ligand cannot bind to the B cell with CD40 receptor to trigger immunoglobulin isotype switching
- **so in a way, you have both T cell and B cell dysfunction in X-linked Hyper IgM syndrome
- thus patients have normal or high levels of IgM with low or absent levels of the other antibodies
What infections are patients with Hyper IgM syndrome at risk for?
-treatment for Hyper IgM syndrome?
- Sinopulmonary infections
- Opportunistic infections with PCP, cryptosporidium
Treatment: IVIG replacement
Which immunizations do not produce an antibody response in patients with IgG subclass deficiency?
Polysaccharide vaccines!
What infections are people with T cell immunodeficiencies at risk for? (3)
- Viral
- Fungal
- Intracellular infections
**disorders of T cell function also often result in B cell antibody production dysfunction because B cells need T cells to function properly = this is combined immunodeficiency
What is the only isolated congenital T–cell immunodeficiency?
DiGeorge syndrome = caused by thymic hypoplasia (thymus makes T cells)
What are the clinical manifestations of DiGeorge syndrome?
-diagnosis?
CATCH-22
- Cardiac defects: TOF most common
- Abnormal facies: low set ears, hypertelorism, hypoplastic mandible, bowing of upper lip
- Thymic hypoplasia & T cell immunodeficiency
- Cleft palate
- Hypoparathyroidism with subsequent hypocalcemia
Diagnosis: genetic testing (FISH) for 22q11 deletion
What are lab results seen with combined immunodeficiency disorders? (3)
- Low lymphocyte count
- Low immunoglobulin levels
- Abnormal response to delayed type hypersensitivity testing (ie. TST)
***This reflects both B and T cell dysfunction since B cells depend on T cells to present antigens for antibody production
What is SCID?
- inheritance patterns?
- mean age of presentation?
Severe combined immunodeficiency = severe T cell dysfunction and resultant B cell dysfunction
- interitance: autosomal recessive (usually ADA = adenosine deaminase deficiency) and X-linked forms
- present by 6 months of age with SEVERE immunodeficiency
- most children die of infection during the first 2 years of life without intervention
What are clinical manifestations of SCID? (7)
- FTT
- Chronic diarrhea
- Chronic candidiasis
- Severe bacterial infection within 1st month of life
- Infection with opportunistic organisms: PCP, cryptosporidium
- Eczema (possibly from GVHD from engraftment of maternal lymphocytes)
- Absent thymus/lymph nodes/tonsils
What condition are patients with SCID at increased risk for developing?
Graft versus host disease: from engrafted maternal T cells or from blood transfusions
-THUS, should always be given irradiated blood products
What is the treatment for SCID?
- Bone marrow transplant is curative
- until BMT can occur, need to give IVIG replacement and PCP prophylaxis and avoid transfusions, no live vaccines
***Enzyme replacement therapy for patients with ADA deficiency can work BUT is not as good as BMT
How do you diagnose Ataxia Telangiectasia?
-findings on bloodwork
- Bloodwork:
- normal IgM and IgG levels but DECREASED IgA and IgG2
- increased serum AFP**** - Definitive diagnosis with gene testing of ATM gene (ataxia-telangiectasia mutated) = DNA repair enzyme