The novel, multiplex, BIOCHIP mosaic-based indirect immunofluorescence (IIF) method has the potential to be a less invasive, rapid, and accurate screening test in patients with bullous pemphigoid (BP), pemphigus vulgaris (PV), and pemphigus foliaceous (PF). This is according to a study published in Journal of the European Academy of Dermatology and Venereology.

To evaluate the diagnostic accuracy of the new BIOCHIP multiplex tool and direct IIF and determine their ability to differentiate between diagnoses of autoimmune bullous disease subtypes, researchers collected sera from patients with BP (n=38), PF (n=8), and PV (n=23). Sera were also collected from control patients who presented to the dermatology clinic for conditions other than BP, PV, and PF (n=63), as well as from healthy volunteers (n=39).

For the IIF multiplex method, the researchers evaluated blinded sera from patients and controls on the same slide. The BIOCHIP mosaic used 10 incubation fields with 6 different substrates, and then compared the results with the positive control sera of pemphigus and BP. The diagnosis of PF and PV was made based on reactivity with monkey esophagus and/or reactivity with desmosomal cadherins (desmoglein [Dsg]1 or Dsg3) and was considered negative if there was no reactivity in any of the 6 biochips.

In 86.8% of the BP patients (n=33), the BIOCHIP mosaic was positive for at least 1 of either structural proteins in the dermo-epidermal junction (BP180 or BP230) substrate. The sensitivity and specificity of the BP180 substrate was 55.3% and 97.7%, compared with 65.8% and 86.5%, respectively, for the BP230 substrate.

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Human salt-split skin substrate was positive in 76.3% of cases, with a specificity of 73.7%. BIOCHIP was positive for 1 or more of either Dsg1 or Dsg3 substrate in 87.5% of patients with PF. The sensitivity and specificity of the Dsg1 substrate was 75% and 97.7%, compared with 62.5% and 70.6%, respectively, for the Dsg3 substrate.

BIOCHIP was positive for either Dsg1 or Dsg3 substrate, or both, in 65.2% of the PV patients. The sensitivity and specificity of the Dsg1 substrate was 13% and 84.5%, compared with 60.9% and 73.6%, respectively, for the Dsg3 substrate in PF.

The researchers found it difficult to accurately interpret the BIOCHIP slides. The intensity of the fluorescence was variable, patchy, and sometimes ambiguous, making interpretation difficult. In an unblinded clinical situation, this could lead to interpretation bias, they wrote.

The researchers suggested that the “BIOCHIP IIF method has high specificity for BP180 and Dsg1 but lower specificity for BP230 and Dsg3.” The BIOCHIP mosaic-based IIF test is potentially a simple, time- and effort-saving test that may aid in the diagnosis and screening of BP, PV, and PF, they concluded.

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Reference

Yang A, Xuan R, Melbourne W, Tran K, Murrell DF. Validation of the BIOCHIP test for the diagnosis of bullous pemphigoid, pemphigus vulgaris and pemphigus foliaceous [published online July 1, 2019]. J Eur Acad Dermatol Venereol. doi: 10.1111/jdv.15770