MLT GlobeImmunology & Serology: Transplant & immunodeficiency – page 3
54 Immunology & Serology MCQs on Transplant & immunodeficiency with answers and explanations.
A baby had delayed umbilical cord separation and now has skin infections without pus. The WBC count shows marked neutrophilia. Flow cytometry would most likely show absent:
Leukocyte adhesion deficiency type I is caused by lack of the beta-2 integrin CD18, so neutrophils cannot leave vessels: high blood neutrophils but no pus. CD19 absence suggests agammaglobulinaemia.
A 28-year-old has recurrent sinus and lung infections. IgG and IgA are low, B-cell numbers are normal and antibody response to vaccines is poor. The most likely diagnosis is:
CVID usually presents after childhood with low IgG plus low IgA or IgM, poor vaccine responses and normal or slightly low B-cell numbers. X-linked agammaglobulinaemia presents in infancy with absent B cells.
In a healthy full-term infant, total serum IgG is normally lowest at about:
Maternal IgG falls after birth while the infant's own production is still low, giving a physiological nadir around 3–6 months. At birth IgG is high because of placental transfer.
A child has eczema, recurrent 'cold' staphylococcal skin abscesses, pneumonias with lung cysts and serum IgE above 2000 IU/mL. The most likely diagnosis is:
Autosomal dominant hyper-IgE (Job) syndrome from STAT3 mutation gives very high IgE, eczema, cold abscesses and pneumatoceles. Wiskott-Aldrich syndrome also has eczema but with thrombocytopenia and small platelets.
A patient with recurrent pneumonia has normal total IgG. Which test best assesses specific antibody function?
Measuring serotype-specific antibodies before and 4–6 weeks after polysaccharide vaccination tests the ability to make functional antibody. Normal total IgG does not exclude specific antibody deficiency.
A kidney transplant recipient on strong immunosuppression has slowly rising creatinine. Which laboratory test is used to screen for polyomavirus nephropathy?
BK polyomavirus reactivates under immunosuppression and can damage the graft; quantitative plasma BK DNA PCR is used for screening and monitoring. Serology is not useful because most adults are already seropositive.
A seronegative stem cell recipient needs transfusion. Which component attribute best reduces the risk of transfusion-transmitted cytomegalovirus?
CMV lives in donor leukocytes, so leukoreduction or use of CMV-seronegative donors reduces transmission. Irradiation prevents TA-GVHD but does not remove CMV.
A 1-year-old boy has eczema, recurrent ear infections and bleeding with low platelets that are small in size. Which immunodeficiency is most likely?
The triad of eczema, thrombocytopenia with small platelets and recurrent infections in a boy is typical of X-linked Wiskott–Aldrich syndrome.
An HIV-positive adult has a CD4 T-cell count of 150 cells/µL. This indicates:
A CD4 count below 200 cells/µL defines AIDS and carries a high risk of opportunistic infections such as Pneumocystis pneumonia. Normal adult CD4 counts are roughly 500–1500 cells/µL.
Before a kidney transplant, the recipient's serum gives a positive crossmatch against donor T lymphocytes. What does this usually mean?
A positive T-cell crossmatch shows preformed antibodies against donor HLA, which can cause hyperacute or acute antibody-mediated rejection, so the transplant is usually not performed.
A newborn screening TREC (T-cell receptor excision circle) assay result is undetectable. This suggests:
TRECs are DNA circles formed during T-cell receptor rearrangement in new thymic emigrants. Absent TRECs show very few new T cells, typical of SCID.
A 'virtual crossmatch' before organ offer is performed by:
A virtual crossmatch predicts compatibility by checking whether the recipient has antibodies against any HLA antigens in the donor's typing, without using donor cells. Mixing serum with donor lymphocytes is a physical crossmatch.
After allogeneic stem cell transplantation, donor engraftment is best monitored in the laboratory by:
STR analysis compares donor- and recipient-specific DNA markers in blood or marrow to measure the percentage of donor cells. ABO typing may not change if donor and recipient share the same group.
A 5-year-old with an unsteady gait and small dilated vessels on the conjunctivae has recurrent sinopulmonary infections and IgA deficiency. Which serum test is typically raised?
Ataxia-telangiectasia (ATM gene) shows ataxia, telangiectasia, IgA/IgG2 deficiency and a characteristically raised serum AFP. IgE is usually low or normal in this disorder.