HLA-B27 testing: A journey from flow cytometry to molecular subtyping

Area of Science:

• Immunogenetics
• Molecular Diagnostics
• Rheumatology

Background:

• Human Leukocyte Antigen B27 (HLA-B27) testing is crucial for diagnosing Ankylosing Spondylitis (AS).
• Evaluating diagnostic methods for HLA-B27 is essential for clinical practice.

Purpose of the Study:

• To compare flow cytometry with DNA microarray for HLA-B27 typing.
• To assess the EUROArray HLA-B27 Direct assay for allele detection and AS/non-AS subtype discrimination in India.

Main Methods:

• Screening of 7543 patients for HLA-B27 using flow cytometry.
• Analysis of 1560 samples by DNA microarray and a subset (n=200) by DNA sequencing for HLA-B27 subtypes.

Main Results:

• Flow cytometry identified 20.56% positive, 73.65% negative, and 5.78% equivocal HLA-B27 cases.
• Microarray detected 85.44% positive and 14.55% negative results among 1560 samples.
• HLA-B*27:07 was the predominant subtype; HLA-B27 cross-reactive subtypes (HLA-B*07, HLA-B*37) were identified in 10% of cases.

Conclusions:

• DNA typing is recommended as a complementary method to flow cytometry for precise HLA-B27 phenotype determination.
• This study is the first to evaluate the EUROArray assay's efficacy for B27 allele detection and non-disease-associated allele identification in the Indian population.