Validation of a multiplex assay for measuring specific IgG4

Purpose: Specific IgG4 (sIgG4) increases with allergen specific immunotherapy and may reflect a state of immune tolerance in food allergy. While ImmunoCAP® has been widely used to measure sIgG4 to a single allergen, PROTIA™ Specific IgG4® has been designed as a multiplex assay for measuring sIgG4. This study sought to validate this assay in comparison to ImmunoCAP®. Materials and Methods: Measurements of sIgG4 were compared between PROTIA™ Specific IgG4® and ImmunoCAP® using sera from 519 allergy patients (asthma: 114, allergic rhinitis: 318, food allergy: 146) with 731 paired tests. sIgG4 was measured against nine inhalant allergens (Dermatophagoides pteronyssinus, Dermatophagoides farinae, cat dander, dog dander, birch pol-len, oak pollen, ragweed pollen, mugwort pollen, and Alternaria alternata spores) and nine food allergens (egg white, casein, wheat, peanut, walnut, crab, shrimp, apple, and peach). Results: PROTIA™ Specific IgG4® showed 95.6% agreement rate with ImmunoCAP® in the positivity comparison. For sIgG4 positivity to each individual allergen, an agreement rate of more than 84.8% was observed. In Cohen’s kappa analysis, these assays displayed substantial correlations [Cohen’s kappa coefficient (κ) ≥0.699], except for shrimp (κ=0.448). Furthermore, both assays displayed strong correlations in quantitative comparisons [correlation coefficients value (ρ) ≥0.8014], except for apple (ρ=0.6571, p=0.175). Serial dilution tests also showed consistency between the assays. Conclusion: PROTIA™ Specific IgG4® showed high consistency with ImmunoCAP® in measuring sIgG4. This assay is applicable to various clinical fields, including allergen immunotherapy and food allergy.