IL-8 ₇₇ isoform in lungs of preterm infants and its processing by neutrophil serine proteases

Introduction: Persistent neutrophilic (PMN) lung inflammation is strongly implicated in the development of Chronic Lung Disease (CLD) of Prematurity. The 72 amino acid (a.a.) chemokine, IL-8 72 , is a key molecule involved in attracting PMNs to sites of inflammation. The longer 77 a.a. isoform (IL-8 77 ) is less potent than IL-8 72 in vitro . We studied expression of IL-8 77 in the preterm ventilated lung and its processing by neutrophil serine proteases. Methods: IL-8 77 was measured by ELISA in bronchoalveolar lavage fluid (BALF) from ventilated preterm infants born at ≤32 weeks gestational age and after conversion by purified PMN serine proteases. Results were compared between the CLD (persistent inflammation) and non-CLD groups (resolved). Results: The majority of IL-8 consisted of the shorter isoforms in the preterm lung (96.3% non-CLD vs 97.1% CLD, p=ns). IL-8 77 expression correlated well with total IL-8 (p<0.0001) but not with gestation (p=ns).Stimulated adult airway-cells and neonatal PMNs and monocytes expressed IL-8 77 as the major isoform, suggesting possible expression in the lung. Preterm BALF significantly converted rhIL-8 77 to shorter isoforms at 18 hours (p<0.05), which was inhibited by α-1 antitrypsin (AAT). Purified neutrophil serine proteases converted IL-8 77 to shorter isoforms dose-dependently and over time. Conclusions: Majority of IL-8 in the ventilated preterm lung are the potent shorter isoforms. Although potentially expressed in the lung, IL-8 77 is probably converted to the shorter isoforms by neutrophil serine proteases. Inhibition of conversion by AAT suggests a potential therapeutic role for it in modulating inflammation in the preterm lung.