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The Biomarker Salivary SP-D May Indicate Small Airway Inflammation and Asthma Exacerbation

Okazaki S1*, Murai H1*, Kidoguchi S2, Nomura E1, Itoh N1, Hashimoto N2, Hamada T2, Kawakita A1, Yasutomi M1, Ohshima Y1

*These authors contributed equally to the manuscript
1Department of Pediatrics, Faculty of Medial Sciences, University of Fukui, Fukui, Japan
2Department of Clinical Laboratory, Faculty of Medial Sciences, University of Fukui, Fukui, Japan

J Investig Allergol Clin Immunol 2017; Vol 27(5) : 305-312
doi: 10.18176/jiaci.0174

Background: Noninvasive and child-friendly biomarkers are important tools for understanding the various phenotypes of childhood asthma.
Objective: The aim of this study was to examine the usefulness of salivary surfactant protein (SP) D in assessing the pathophysiology of childhood asthma.
Methods: We measured salivary concentrations of SP-D and forced oscillation technique (FOT) indexes in 19 healthy controls and 21 asthmatic children. Regression equations for the predictive values of FOT indexes were generated from healthy controls. We analyzed the correlations between salivary SP-D concentration and percentages of the predictive values of FOT indexes, as well as the severity of exacerbation.
Results: We found that salivary SP-D levels were higher in asthmatic children than in healthy controls. In the asthmatic children, salivary SP-D levels correlated with the percentages of predicted differences in resistance between 5 Hz and 20 Hz (%R5-R20), which represented the resistance of peripheral airways, and with the severity of asthma exacerbation.
Conclusion: Salivary SP-D may reflect asthmatic inflammation in peripheral small airways and may be a useful marker for monitoring the degree of exacerbation in childhood asthma.

Key words: Asthma, Biomarkers, Children, Forced oscillation technique, Salivary SP-D