Abstract 92

Background: Leukocyte trafficking to inflammatory sites is initiated by leukocyte rolling mediated by the selectin family of adhesion molecules. Adhesion of leukocytes to endothelial cells and extravasation in the intraalveolar space is thought to be critical for induction of acute lung injury. Recently, we identified several intracellular signalling cascades upon L-selectin triggering in leukocytes, resulting in synthesis of oxygen radicals, actin polymerization, activation of the neutral sphingomyelinase and the Ras/MAP-kinase pathway. Aim of the present study is to examine potential effects of surfactant on L-selectin induced signalling.

Methods: Immune fluorescence, kinase/sphingomyelinase assays, flow cytometry in L-selectin stimulated T-lymphocytes preincubated with surfactant.

Results: Treatment of lymphocytes with different surfactant preparations (Exosurf™, Curosurf™) blocks L-selectin induced lymphocyte activation. In particular, surfactant prevented capping of the L-selectin receptor molecule and the activation of the src-like tyrosine kinase p56lck after L-selectin triggering. Furthermore, the neutral sphingomyelinase, which is also activated by L-selectin, is inhibited by surfactant already in resting cells. Surfactant did not influence receptor binding by antibodies as shown in FACS-analysis.

Conclusions: Surfactant inhibits at least two independent signalling pathways triggered by L-selectin stimulation. The attenuation of L-selectin signalling might result in modulation of leukocyte function and may contribute to the anti-inflammatory effects of surfactant. Supported by a grant from the University Heidelberg