ABSTRACT
Treatment of rainbow trout macrophages with glycyrrhizin (GL), an aqueous extract of licorice (Glycyrrhiza glabra), enhanced their respiratory burst activity. Maximal effects were seen using concentrations of 10-100 ug/ml. GL also modulated trout lymphocytes, increasing proliferation responses to the mitogen phytohemagglutinin two-fold over a range of GL concentrations. In addition, GL elicited the release of a macrophage activating factor (MAF) kom head kidney leukocytes, as assessed by the ability of generated supernatants to increase respiratory burst activity of target macrophages. MAF activity was most apparent using 100 ug/ml GL to induce MAF release and a 48 h incubation period with the target macrophages. Finally, GL was shown to enhance the release oF MAF in response to the mitogen concanavalin A. The results suggest that GL might modulate the innate defences in fish.