CHT Antibody Detection & Characterization 2 — Questions and Answers
Question 1: Non-HLA antibodies have been implicated in transplant rejection. Which non-HLA target is most studied?
- MICA (MHC class I chain-related antigen A) (Correct answer)
- ABO blood group antigens
- Lewis blood group antigens
- Kell blood group antigens
Correct answer: MICA (MHC class I chain-related antigen A)
MICA is a stress-induced cell surface molecule encoded in the MHC region; anti-MICA antibodies have been associated with rejection and graft loss independent of HLA.
Question 2: Which immunoglobulin subclass of IgG most efficiently activates complement and is most associated with acute AMR?
- IgG1 and IgG3 (Correct answer)
- IgG2 and IgG4
- IgG4 only
- IgG2 only
Correct answer: IgG1 and IgG3
IgG1 and IgG3 are the most potent complement-activating IgG subclasses and are strongly associated with antibody-mediated rejection.
Question 3: What does it mean when DSA is described as 'complement-binding' in the clinical context?
- The antibody can activate the classical complement cascade, increasing rejection risk (Correct answer)
- The antibody blocks complement from injuring the graft
- The antibody is detected only by CDC assay
- Complement is bound to the antibody preventing it from binding HLA
Correct answer: The antibody can activate the classical complement cascade, increasing rejection risk
Complement-binding DSA (e.g., C1q-binding or C3d-fixing) indicates the antibody can activate complement, which is associated with more severe AMR and worse graft outcomes.
Question 4: In Luminex-based crossmatch (LCM/FCXM by bead), what advantage does it have over traditional CDC crossmatch?
- Higher sensitivity for detecting low-level HLA antibodies (Correct answer)
- Can detect non-HLA antibodies only
- Requires live donor cells for testing
- Less expensive and faster turnaround
Correct answer: Higher sensitivity for detecting low-level HLA antibodies
Luminex and flow cytometric crossmatches are significantly more sensitive than CDC, detecting antibody levels too low to activate complement but still potentially harmful.
Question 5: What is the purpose of DTT (dithiothreitol) treatment of serum in HLA antibody testing?
- Inactivates IgM antibodies by breaking disulfide bonds to allow IgG-only testing (Correct answer)
- Removes complement components from serum
- Concentrates antibodies by protein precipitation
- Inactivates lipopolysaccharide contamination
Correct answer: Inactivates IgM antibodies by breaking disulfide bonds to allow IgG-only testing
DTT cleaves the disulfide bonds that hold IgM pentamers together, inactivating IgM antibodies so the assay result reflects only IgG antibodies.
Question 6: Which type of HLA antibody specificity is considered most critical to identify before transplantation?
- Donor-specific antibodies (DSA) directed against the specific donor's HLA antigens (Correct answer)
- Any HLA class I antibody regardless of donor type
- MICA antibodies only
- Anti-HLA-DP antibodies only
Correct answer: Donor-specific antibodies (DSA) directed against the specific donor's HLA antigens
DSA against the specific donor's HLA antigens are the most clinically critical to identify, as they predict positive crossmatches and risk for hyperacute and AMR.
CHT Antibody Detection & Characterization 2
Non-HLA antibodies have been implicated in transplant rejection.
Which non-HLA target is most studied?