Characterization of plasma secretory phospholipase A2 activity in the prairie rattlesnake (Crotalus viridis)

Abstract

Background: Plasma phospholipase A 2 (PLA 2 ) enzyme activity is a key component of innate immunity in most vertebrates. We evaluated circulating secreted PLA 2 activity of prairie rattlesnakes (Crotalus viridis) by incubation of plasma with bacteria labeled with fluorescent membrane lipids. Results: Incubation of bacteria with increasing volumes of plasma resulted in volume-dependent lysis of fatty acids from bacterial membranes. The activity was rapid, with substantial activity recorded after only 5 min of incubation with labeled bacteria, and a linear response for 20 min. In addition, the lysis activity was temperature-dependent, increasing activities from 5 to 20°C, peak activities at 25-30°C, and then decreasing activities from 35 to 40°C. Furthermore, the activity was inhibited in a concentration-dependent manner by p-bromophenacyl bromide, a specific inhibitor of PLA 2 activity, which indicated that the observed activities were due to the presence of PLA 2 in the plasma of C. viridis.Conclusions: This study represents the first description of secretory PLA 2 activity in the plasma of a snake. Our study shows that in addition to being an important component of snake venom, PLA 2 enzymes play an important role in the snake's immune response.