Characterization of Innate Immunity of the Prairie Rattlesnake (Crotalus viridis)

Merchant, Mark

mmerchant@mcneese.edu

Department of Chemistry

McNeese State University

Lake Charles, Louisiana, USA

Baker, Sarah*

Illinois Natural History Survey

1816 S Oak Street

Champaign, Illinois, USA

* Present Address:

Arizona Game and Fish Department

5000 W Carefree Highway

Phoenix, Arizona, USA

The innate immune system functions to respond quickly to pathogenic challenge and is likely the primary line of defense for ectothermic vertebrates. Snake populations are declining globally, and disease has been identified as a significant threat. However, few studies have been done investigating snake immune systems. To characterize innate immunity, we measured the antibacterial properties and complement activity of plasma collected from 20 captive Prairie Rattlesnakes (Crotalus viridis). Results from antibacterial studies showed that rattlesnake plasma was effective at killing six Gram-negative and two Gram-positive bacterial species in vitro. The antibacterial activities were rapid, inhibiting 73% of E. coli growth within 20 minutes of exposure. The antibacterial activities were also protease-sensitive, heat labile, and inhibited by chelators of divalent metal ions, suggesting that these activities were due to the presence of serum complement activity. We employed a spectrophotometric sheep red blood cell (SRBC) hemolysis assay to assess serum complement activity in rattlesnake plasma. The complement-mediated hemolysis of SRBCs showed the same concentration-dependent, kinetic, and mechanistic characteristics as the antibacterial activities, confirming that the antibacterial activities observed were primarily due to the action of serum complement activity.