MLT GlobeImmunology & Serology: Transplant & immunodeficiency – page 2
54 Immunology & Serology MCQs on Transplant & immunodeficiency with answers and explanations.
Corneal transplants are rejected less often than most organ grafts mainly because:
The cornea has no blood vessels and limited lymphatic access, so it is relatively protected from immune attack (immune privilege).
The main purpose of immunosuppressive drugs after organ transplantation is to:
Immunosuppressants such as tacrolimus, cyclosporine and mycophenolate suppress the recipient's immune response so that the graft is not rejected.
A major side effect of long-term immunosuppression after transplantation is an increased risk of:
Suppressing immunity reduces defence against microbes and tumour cells, so transplant recipients have more opportunistic infections and virus-related cancers.
Which virus is a major cause of infection after organ and stem cell transplantation and is often monitored by PCR?
Cytomegalovirus reactivation or transmission with the graft is a common and serious complication in transplant recipients, so CMV DNA is often monitored by quantitative PCR.
A person who cannot make J chain would lack secretory IgA. Recurrent infections would most likely involve the:
Without J chain, polymeric IgA cannot be transported by the polymeric Ig receptor to mucosal surfaces such as the gut.
One autosomal recessive form of SCID results from deficiency of which enzyme?
ADA deficiency causes toxic metabolites that kill lymphocytes.
A kidney graft turns cyanotic and fails within minutes of reperfusion. This is most likely:
Preformed anti-ABO or anti-HLA antibodies fix complement on graft endothelium immediately. Acute rejection occurs over days to months; chronic over months to years.
Before solid-organ transplantation, which laboratory workup best reduces the risk of rejection?
ABO incompatibility and preformed anti-HLA antibodies cause hyperacute rejection, so ABO grouping, HLA typing and crossmatching are essential. Rh is not a major barrier in solid organs.
In a complement-dependent cytotoxicity (CDC) crossmatch, the test uses:
Recipient serum is incubated with donor lymphocytes and complement. Cell death shows donor-specific cytotoxic antibody, a contraindication to transplant.
Compared with the CDC crossmatch, the flow cytometric crossmatch:
Flow crossmatch uses fluorescent anti-human IgG to detect antibody bound to donor T and B cells, including antibodies that do not fix complement. It is more sensitive than CDC.
Panel reactive antibody (PRA) or calculated PRA (cPRA) in a transplant candidate estimates:
cPRA expresses the percentage of the donor population with HLA antigens to which the candidate has antibodies. A high cPRA means the patient is highly sensitised and harder to match.
Which HLA typing method gives the highest (allele-level) resolution?
Sequencing-based typing, especially next-generation sequencing, defines HLA alleles at high resolution. Serologic typing only defines broad antigen groups.
A child with recurrent catalase-positive infections (such as Staphylococcus aureus and Aspergillus) has an abnormal dihydrorhodamine (DHR) flow test. The diagnosis is:
Chronic granulomatous disease is a defect of NADPH oxidase, so neutrophils cannot produce an oxidative burst. The DHR test replaced the nitroblue tetrazolium (NBT) test.
Which laboratory pattern best fits hyper-IgM syndrome due to CD40 ligand deficiency?
CD40L on T cells is needed for B-cell class switching. Without it, B cells make IgM but little IgG, IgA or IgE.
Absolute CD4 count is calculated as WBC × % lymphocytes × % CD4+ lymphocytes. For WBC 5.0 × 10⁹/L, lymphocytes 20% and CD4+ 15% of lymphocytes, the CD4 count is:
5000/µL × 0.20 = 1000 lymphocytes/µL; 1000 × 0.15 = 150 CD4 cells/µL. A value below 200 cells/µL defines AIDS in an HIV-infected person.
Which assay identifies the exact HLA specificities of a transplant candidate's antibodies most precisely?
Single-antigen beads each carry one HLA antigen, so the fluorescence pattern shows the exact specificity of each antibody. A CDC crossmatch only shows whether antibody reacts with one donor's cells.
Cellular blood components for a stem cell transplant recipient are irradiated. The main purpose is to:
Gamma or X-ray irradiation (at least 25 Gy to the centre of the bag) stops donor T lymphocytes from proliferating, preventing TA-GVHD. Leukoreduction, not irradiation, reduces febrile reactions and CMV transmission.
Blood for monitoring tacrolimus levels in a transplant recipient should be:
Tacrolimus is concentrated in red cells, so whole blood (EDTA) is measured, usually as a trough level just before the next dose. Serum or plasma would give falsely low values.
Cyclosporine and tacrolimus suppress rejection mainly by:
Calcineurin inhibitors prevent NFAT activation in T cells, reducing transcription of IL-2 and T-cell proliferation. CD20 depletion is the action of rituximab.
A 4-month-old boy has severe infections and very low T and NK cells with normal B-cell numbers. The most likely defect is in the:
X-linked SCID from IL2RG mutation (T−B+NK−) blocks IL-7 and IL-15 signalling needed for T and NK development. Bruton tyrosine kinase defects cause absent B cells with normal T cells.