A simple method to study the activity of natural compounds on the chemiluminescence of neutrophils upon stimulation by immune complexes.

Introduction: Neutrophils (PMNs) are the main effector cells involved in the immune response to microorganisms. However, in various noninfectious states, such as autoimmune and immune complex (ICs) diseases, ICs are found to be deposited in various organs, leading to recruitment and activation of PMNs at these sites of deposition. Consequently, reactive oxygen species (ROS) and lysosomal enzymes are extensively released by activated PMNs into the extracellular milieu, leading to host tissue injury.

Methods: In the present study, we discuss some experimental conditions of a luminol-enhanced chemiluminescence (LECL) assay to study the effect of natural compounds on the production of ROS by rabbit PMNs stimulated with precipitated ICs. Moreover, we evaluated the activities of quercetin and 7-allyloxycoumarin on this ROS-producing system and their toxicity to PMNs.

Results: Both compounds had concentration-dependent inhibitory effects on LECL. Quercetin at concentration of 5 micromol/l inhibited 94.5+/-1.0% of LECL, whereas 7-allyloxycoumarin at concentration of 200 micromol/l inhibited 53.8+/-2.4% of LECL. Neither compound was toxic to PMNs under the tested conditions.

Discussion: The proposed method may be useful for the screening of nontoxic compounds that can modulate ROS production by IC-stimulated PMNs. Special attention should be devoted to natural compounds from higher plants, since their potential as sources of new drugs is still largely unexplored.