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

Comparative study of two laboratory techniques for the detection of HLA-B27 in patients with axial spondyloarthritis: a cross-sectional analysis

BACKGROUND

The diagnostic and prognostic relevance of Human Leukocyte Antigen B-27 (HLA-B27) in Axial Spondyloarthritis (AxSpA) is undeniable, with 70% of Ankylosing Spondylitis (AS) patients carrying the B27 gene, contrasted with a mere 4.35% in the general population. Flow cytometry (FC) and Polymerase Chain Reaction (PCR) have emerged as the predominant techniques for routine HLA-B27 typing. While various studies have compared these methods, none have catered to the unique characteristics of the Brazilian demographic. Therefore, this research aims to compare FC and PCR in a Brazilian cohort diagnosed with AxSpA.

METHODS

An analytical cross-sectional study was undertaken involving 62 AxSpA outpatients from a Brazilian University Hospital. Both FC and PCR-SSP assays were utilized to ascertain HLA-B27 typing. The outcomes (either confirming or refuting the allele's presence) underwent rigorous scrutiny. Agreement between the methodologies was assessed using the kappa statistic. A p-value of < 0.05 was deemed statistically significant.

RESULTS

Of the participants, 90.3% (n = 56) were HLA-B27 positive according to FC, while 79% (n = 49) were identified as positive using the PCR method. FC exhibited a sensitivity rate of 98% paired with a specificity of 38.5%. The Positive Predictive Value for FC stood at 85.7%, and the Negative Predictive Value was 83.5%. Consequently, the overall accuracy of the FC method was gauged at 85.5%. A kappa coefficient of κ = 0.454 was derived.

CONCLUSIONS

FC demonstrated noteworthy sensitivity and satisfactory accuracy in HLA-B27 detection, albeit with a reduced specificity when contrasted with PCR-SSP. Nevertheless, given its cost-effectiveness and streamlined operation relative to PCR, FC remains a pragmatic option for preliminary screening in clinical practice, especially in low-income regions. To optimize resource allocation, we advocate for a refined algorithm that initiates by assessing the relevance of HLA-B27 typing based on Choosing Wisely recommendations. It then leans on FC, and, if results are negative yet clinical suspicion persists, advances to PCR. This approach aims to balance diagnostic accuracy and financial prudence, particularly in regions contending with escalating medical costs.

Human leucocyte antigen-B27 testing in clinical practice: a global perspective

PURPOSE OF REVIEW

The association between human leucocyte antigen (HLA)-B27 and spondyloarthritis (SpA) was described half a century ago. New insights about pathophysiologic pathways and their role in bone formation were reported in recent years and will be discussed in this review.

RECENT FINDINGS

There is a considerable variation in the association between HLA-B27 and SpA across the globe, with the strongest association reported in populations of Northern European and Asian descent and the lowest in the Middle East and Africa. Other genes are also involved in disease susceptibility, highlighting the importance of newly proposed weighted genetic scores to support the diagnosis. On the global level, the interaction between genetic background and gut dysbiosis seems critical for disease predisposition. As for the individual patient, the presence of HLA-B27 can have a significant influence on SpA diagnosis and disease phenotype. More importantly, new studies suggested a role for HLA-B27 in radiographic damage in the sacroiliac joints and the progression of bone formation in the spine.

SUMMARY

Findings in recent years have enhanced our understanding of the role of HLA-B27 in the pathophysiology and in disease-related bone formation in SpA, which may pave the way for new therapeutic targets.

Comparison of Next-Generation Sequencing-Based Human Leukocyte Antigen Typing with Clinical Flow Cytometry and Allele-Specific PCR Melting Assays for HLA-B27 Genotyping

BACKGROUND

Due to the strong association between ankylosing spondylitis and Human Leukocyte Antigen (HLA)-B27, accurate identification of HLA-B27 is important in the diagnosis of patients with suspected spondyloarthritides. For this study, we compared a high-resolution HLA-B typing method to the clinical flow cytometry and allele-specific PCR melting assays to determine clinical benefits of high-resolution testing.

METHODS

Residual clinical samples submitted for HLA-B27 testing by flow cytometry were tested by single-locus HLA-B genotyping using next-generation sequencing (NGS), and PCR with melting curve analysis, currently used as a reflex test for indeterminate flow cytometry results.

RESULTS

Fifty out of the 51 samples (98%) positive by flow cytometry confirmed as HLA-B27 positive by PCR melting assay and by NGS. The sample that did not confirm was genotyped as HLA-B*07:02. All the samples negative by flow cytometry were confirmed as HLA-B27 negative by both PCR melting assay and NGS. For the group that was indeterminate by flow cytometry, 84.5% (n = 49) typed as positive for HLA-B27, while 15.5% (n = 9) were negative for HLA-B27 but positive for HLA-B*07:02. NGS was the only method able to distinguish between pathogenic and nonpathogenic HLA-B27 variants, in contrast to the flow cytometry or the PCR melting assays.

CONCLUSIONS

Single-locus NGS is superior to flow cytometry and PCR melting assay for the unambiguous identification of HLA-B27 variants, and uniquely able to distinguish between pathogenic and nonpathogenic B27 alleles. Due to its high accuracy, it may be a feasible superior alternative to flow cytometry and traditional molecular methods for clinical HLA-B27 testing.

What Does Human Leukocyte Antigen B27 Have to Do with Spondyloarthritis?

Human leukocyte antigen (HLA) B27 is the key laboratory parameter for axial spondyloarthritis (axSpA). Its prevalence is variable across different geographic zones and ethnicities, and often mirrors the prevalence of axSpA. HLA-B27 plays a role in axSpA physiopathology. It is correlated with spondyloarthritis phenotype with a consistent positive association with family history, early disease onset, shorter diagnostic delay, hip involvement, and acute anterior uveitis. HLA-B27 has a pivotal role in many referral strategies. However, these strategies were developed in European populations and need to be evaluated in populations with lower HLA-B27 background prevalence, and where additional parameters might be needed.

Real-time PCR based HLA-B*27 screening directly in whole blood

The linkage between the occurrence of human leucocyte antigen B*27 (HLA-B*27) and ankylosing spondylitis or other related spondyloarthritides is well documented. PCR based methods are widely used for HLA-B*27 screening. To refine HLA-B*27 testing we aimed at establishing a real-time PCR protocol to detect the HLA-B*27 allele directly in blood samples, without DNA extraction. HLA-B*27 analysis was performed by two real-time PCRs using TaqMan primer-probe assays for B*27 specific amplification of exon 2 or exon 3 of the HLA-B gene together with a mutant of Taq polymerase for direct blood PCR. Conditions for direct blood PCR were optimized and the reliability of the direct blood PCR protocol was evaluated by re-genotyping over 200 blood samples from patients who previously underwent routine DNA-based HLA-B*27 testing. Heating blood samples at 95°C for 10 minutes significantly improved PCR performance. Results from real-time PCR based HLA-B*27 testing directly in blood of over 200 patients were in 100% concordance with results obtained by routine DNA-based HLA-B*27 genotyping. In summary, we present a reliable real-time PCR protocol for HLA-B*27 screening directly in whole blood supporting fast clarification of the presence of ankylosing spondylitis or other spondyloarthritides in suspected cases.

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

BACKGROUND

Determination of HLA-B27 status plays an important role as adjuvant in suspected cases for diagnosis of Ankylosing Spondilytis (AS). Objectives of this study were to evaluate (i) flow cytometry method in comparison with DNA microarray for HLA-B27 typing and (ii) EUROArray HLA-B27 Direct assay for HLA-B27 allele detection along with discrimination of AS/non-AS subtypes in Indian population.

METHODS

A total of 7543 patients with a presumptive clinical diagnosis of AS were referred for screening of HLA-B27. All samples were initially tested by flow cytometry, and based on its findings, 1560 samples were analyzed for the presence of HLA-B27 allele by microarray technology. A subset of samples (n = 200) were further tested by DNA sequencing for identification of HLA-B27 subtypes.

RESULTS

Screening of HLA-B27 by flow cytometry reported 1551 positive (20.56%) and 5556 negative (73.65%) cases. Remaining 436 (5.78%) samples were identified within equivocal zone. Of cases (n = 1560) analyzed by microarray method, 1333 (85.44%) and 227 (14.55%) were detected microarray positive and negative, respectively. DNA sequencing identified HLA-B*27:07 as the predominant subtype among cases showing ex2 positivity by microarray method. Of 200 cases, 20 cases (14 of HLA-B*07 and 6 of HLA-B*37) of HLA-B27 cross-reactive subtypes were also identified.

CONCLUSION

We recommend DNA typing as a complementary tool along with flow cytometry to accomplish successful HLA-B27 phenotype determination. This is the first study among Indian population to evaluate efficacy of EUROArray to detect B27 allele and its potential to indicate the presence of nondisease-associated alleles in Indian population.