An improved assay for detection of sputum periostin in patients with asthma

<b>Background:</b> Circulating periostin associates with markers of type 2 inflammation in patients with asthma. Less is known about local airway periostin as detection levels in sputum are low using currently available periostin assays. <b>Aim:</b> To investigate detection levels of sputum periostin using two different periostin assays. <b>Methods:</b> Periostin levels were measured by ELISA as described (Okamoto et al. ERJ.2011;37:1119), using two assays with antibodies against different periostin protein epitopes (R1 and R4 in assay 1, R1 and R2 in assay 2). Assay reactivity was compared by Western blotting. Sputum (and matched serum) samples were available from n=107 mild-to-moderate and severe asthmatic patients from the European study BIOAIR (James et al. AJRCCM.2016;193:131). <b>Results:</b> Periostin was detectable in 39% of sputum samples using assay 1 and 90% of sputum samples using assay 2. Results of the two assays correlated (r=0.7, p&lt;0.0001). Only assay 2 detected cleavage products of periostin, as well as periostin monomers and oligomers. Sputum periostin (assay 2) showed several correlations with relevant clinical characteristics, table 1. <b>Conclusion:</b> We describe an assay for improved detection of sputum periostin. Local sputum periostin levels may show greater associations to airway inflammation than circulating periostin.