Abstract 49

Introduction This study a) compares the concentrations of interleukin-1β [IL-1β], IL-1 receptor antagonist [IL-1ra] and type II soluble receptor of IL-1 [IL-1sRII] in the blood and lungs to identify whether separate pools of the cytokines exists in each compartment, and b) investigate respective IL-1β bioactivity.

Method Simultaneous blood and bronchoalveolar lavage (BAL) samples were taken at predetermined times over 3 weeks in 15 neonates (mean gestation=27 wks), yielding 60 samples, and the concentrations of the 3 cytokines were measured.

Results Median (range) [IL-1β] (pg/ml) was considerably greater in BAL fluid than in serum 80.3 (0.8-5509) vs 2.2 (undetectable-48) (p<0.05). [IL-1ra] were similar in each compartment 6400 (540-190000) vs 11000 (680-14000) (p=0.6) while [IL-1sRII] were far lower in BAL 2300 (220-61000) vs 21000 (4600-92000) (p<0.001).

Conclusion Different pools of IL-1β and IL-1sRII were identified in the two compartments. The results demonstrate that IL-1β bioactivity is greater in neonatal lungs than in serum. Serum [IL-1β] do not accurately reflect lung IL-1β is a smaller molecule than albumin so it may leak to the systemic circulation.