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Salivary SP-D may be a biomarker reflecting small airway inflammation and asthma exacerbation

Shintaro Okazaki1*, Hiroki Murai1*, Shuhei Kidoguchi2, Eishi Nomura1, Naohiro Itoh1, Norikazu Hashimoto2, Toshihiko Hamada2, Akiko Kawakita1, Motoko Yasutomi1, Yusei Ohshima1

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

J Investig Allergol Clin Immunol 2017; Vol. 27(5)
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 elevated in asthmatic children compared to healthy controls. In the asthmatic children, salivary SP-D levels correlated with the percentages of predicted differences in resistance between 5Hz and 20Hz (%R5-R20), representing 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.