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Elevated blood levels of thymus and activation-regulated chemokine (TARC)/CCL17 have been observed in atopic dermatitis (AD) and may serve as a new biomarker for AD. However, the normal levels, especially in children, have not been well determined. We sought to establish an efficient enzyme-linked immunosorbent assay (ELISA) with a wide range of detection that would be suitable for measurement of serum TARC/CCL17 and to determine the normal ranges of this chemokine in different age groups and its diagnostic usefulness for AD. A sensitive specific ELISA for TARC/CCL17, which we previously reported, was modified to accommodate the wide range of TARC/CCL17 values often found in sera. Twenty-seven children with AD under 6 yr of age and 25 age-matched normal non-atopic controls, and 18 patients with AD and 27 controls who were 6 yr and older were enrolled. The severity of AD was evaluated using the SCORAD index. The serum levels of TARC/CCL17 were measured with the ELISA, and the serum levels of IP-10/CXCL10 were also measured. With the novel ELISA system, the assayable range of TARC/CCL17 was 14-8000 pg/ml, and the coefficient of variation at various concentrations ranged from 2.3% to 5.0%. The serum levels of TARC/CCL17 in normal individuals were significantly higher in young children, especially in the age group of 0-1 yr. The cut-off values of TARC/CCL17 for the diagnosis of AD were 1431 pg/ml for 0-1 yr group, 803 pg/ml for 2-5 yr group and 510 pg/ml for the 6 yr and older group, with high sensitivity and specificity of 0.83 and 0.93, 0.83 and 0.92, 0.85 and 0.96, respectively. The magnitude of the decrease in the SCORAD index after treatment with topical steroids correlated significantly with the decrease in serum TARC/CCL17. There was no difference in the serum levels of IP-10/CXCL10 between AD and the controls. The TARC/CCL17:IP-10/CXCL10 ratio tended to be higher in the control children aged 0-1 yr than in those aged 2-5 yr. The serum level of TARC/CCL17 reflects the severity and therapeutic response in AD. The high normal levels in infants should be taken into account when assaying TARC/CCL17.

Abstract. Oxygenated organic aerosol (OOA) observed in remote areas is believed to comprise aged secondary organic aerosol (SOA); however, the reaction processes relevant to SOA chemical aging have hitherto been unclear. We recently measured the mass spectra of SOA formed from the photooxidation of aromatic hydrocarbons using an Aerodyne aerosol mass spectrometer (AMS) and reported that SOA aging is slowed with increasing number of alkyl groups in the precursor molecule. In this study, we selected benzene and 1,3,5-trimethylbenzene (TMB) as precursors to analyze SOA formed from the photooxidation of aromatic hydrocarbons in the presence of NOx using high-resolution time-of-flight AMS (H-ToF-AMS) and liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS). A van Krevelen diagram was studied using the O/C and H/C ratios obtained by H-ToF-AMS for organics present in SOA. The results showed these organics to be rich in carboxylic acids or hydroxycarbonyls and the O/C ratio of SOA formed by the reaction of 1,3,5-TMB to be lower than that for benzene. Analytical results from LC/TOF-MS showed the particulate products formed by the reaction of 1,3,5-TMB to be richer in ketocarboxylic acids than for benzene. These results indicate that SOA aging proceeds mainly by formation of carboxylic acids and that the rate of SOA aging in laboratory chambers is limited by the oxidation of ketone groups. SOA formed in laboratory chamber experiments is less oxidized than for ambient OOA, not only because the experimental duration is insufficient or the SOA mass loading in the chamber is higher than that of the atmosphere. The laboratory chamber experiments under dry conditions are not able to simulate ketocarboxylic acid photochemical oxidation in the aqueous phase. The fractions of organic peroxides to the total SOA mass were determined by iodometric spectrophotometry to be 12 ± 8% (1,3,5-TMB) and <39% (benzene). Further, it was newly found that, unlike the reaction of benzene, only very small amounts of nitrophenols are produced by the reaction of 1,3,5-TMB.

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