BACKGROUND: The atopy patch test (APT) is an in vivo model to study the 
induction of eczema by inhalant allergens in atopic dermatitis (AD) patients. 
Mepolizumab is a monoclonal antibody to interleukin-5, which reduces peripheral 
blood eosinophils. Previously, we reported that mepolizumab treatment did not 
result in clinical improvement in AD. The current study investigates the effect 
of mepolizumab therapy on the APT in the same patients.
METHODS: Mepolizumab treatment was given at days 0 and 7 in a double-blind 
placebo-controlled design. The APT was applied at days -2, 0, 14 and 28. 
Clinical evaluation of each APT was conducted 48 h after application at days 0, 
2, 16 and 30. Skin biopsies were taken at days 0, 2 and 16 for eosinophil 
counts.
RESULTS: The mepolizumab-treated group showed no significant reduction in 
macroscopic outcome of the APT. Tissue eosinophils were reduced in the 
mepolizumab-treated group at day 16 compared with placebo; however, this was not 
significant.
CONCLUSION: Mepolizumab therapy cannot prevent the eczematous reaction induced 
by the APT. Furthermore, the influx of tissue eosinophil numbers in the APT is 
not significantly inhibited after mepolizumab treatment compared with placebo, 
despite a significant reduction in peripheral blood eosinophils.