Detection and specification of noncomplement binding anti-HLA alloantibodies

Area of Science:

• Immunology
• Transplantation Science

Background:

• Alloimmunization against human leukocyte antigens (HLA) is a major barrier to successful kidney retransplantation.
• Understanding the specific immunoglobulin (Ig) isotypes and subclasses of anti-HLA antibodies is critical for accurate patient assessment.

Purpose of the Study:

• To investigate the distribution of HLA-specific Ig isotypes and subclasses in patients awaiting kidney retransplant.
• To determine the prevalence and specificity of noncomplement-binding IgG2 and IgG4 alloantibodies in this patient cohort.

Main Methods:

• Sera from 102 kidney retransplant candidates were analyzed for anti-HLA antibodies using complement-dependent cytotoxicity (CDC+DTT) and enzyme-linked immunosorbent assay (ELISA).
• Ig isotypes/subclasses (IgG1-4, IgA1-2, IgM) were identified using isotype-specific secondary antibodies.
• HLA specificities of IgG2 and IgG4 antibodies were compared to donor mismatches.

Main Results:

• 37% of sera were positive for class I HLA antibodies by CDC+DTT, 40% by class I ELISA, and 46% by class II ELISA.
• IgM antibodies were detected in 17% of sera, while IgA antibodies were not detected.
• Noncomplement-binding IgG2 and/or IgG4 antibodies were found in 25% of sera, with 88% directed against donor antigens.

Conclusions:

• Donor-specific noncomplement-binding IgG2 and IgG4 alloantibodies are highly prevalent in HLA-immunized kidney retransplant candidates.
• Thorough antibody screening, including CDC and ELISA, and defining Ig isotypes/subclasses are essential for pre-transplant evaluation.
• This approach can help explain inconsistent antibody screening results and improve patient management.