T U E S D A Y 852 Activity of Natural Moisturizing Factor Forming Enzyme Bleomycin Hydrolase in Atopic Dermatitis Affected By Disease Control Status and Seasonal Change Takeshi Chiba, MD; Division of Allergy, National Center for Child Health and Development, Tokyo, Japan. RATIONALE: Bleomycin hydrolase (BH) is thought to have an important physiological role by localizing at the stratum corneum (SC) in mammalian skin, and generating free amino acids from citrullinated peptides in the last step of filaggrin degradation pathway. In this study, we investigated whether disease activity and seasonal change affected BH activity. METHODS: We recruited 11 poorly controlled AD children (SCORAD>25), 51 well-controlled AD children (SCORAD<10) and 27 healthy volunteer children aged 15 or younger. SC samples were collected from the forearms in summer and winter using the tape-stripping technique. BH activity was measured using a fluorescent substrate, citrullinated aminomethylcoumarine as a substrate. RESULTS: BH activity was low in summer across all three groups. In winter, the activity elevated significantly in both the well-controlled AD and healthy groups, but not in the poorly controlledAD group. (summer vs. winter: well-controlled, 29620.3 pmol/mg/min vs. 174.26156.8 pmol/ mg/min, p<0.0001; poorly controlled, 24.0265.24 pmol/mg/min vs. 28.41610.4 pmol/mg/min, p50.252). In winter, BH activity of poorly controlled AD was significantly lower than that of well-controlled AD and healthy controls. (healthy vs. poorly controlled in winter: mean (SD), 76675.0 pmol/mg/min vs. 28610.9 pmol/mg/min, p50.013). CONCLUSIONS: BH activity is affected by seasonal change and disease control status. Regardless of the baseline severity of AD, the skin barrier can be recovered with improved BH activity as a result of appropriated treatment of AD.