Abstract
Incubation of different volumes of serum from the Komodo dragon (Varanus komodoensis) with sheep red blood cells (SRBCs) resulted in volume-dependent hemolysis, as measured spectrophotometrically at 540 nm. The hemolysis occurred rapidly, with almost 90% of the hemolytic activity occurring within 20 min of incubation. A thermal profile showed that Komodo dragon serum exhibited low activity from 5- 20℃, but exerted maximum activity at 35℃, which was substantially reduced at 40℃. The maximum activity was observed near optimal temperatures to which Komodo dragons thermoregulate. Mild heat treatment of Komodo dragon serum (56℃, 30 min) depleted the ability to hemolyze SRBCs. In addition, preincubation of Komodo dragon serum with only 5 mM EDTA or phosphate, both chelators of divalent metal ions, reduced the hemolytic activity sharply. These results indicate that the hemolytic activity was due to the presence of a potent serum complement system. Incubation of Komodo dragon serum with 5 mM EDTA and 15 mM Ca2+ or Mg2+, but not Ba2+, Zn2+, or Fe2+, completely restored activity. These results indicate that Komodo dragon serum complement activity requires the presence of Mg2+ or Ca2+. This is the first assessment of innate immune activity of a Varanid.
Highlights
Innate immunity comprises that part of microbial defense which responds in a non-specific manner to infiltration by microbes
Exposure of different dilutions of serum from Varanus komodoensis to sheep red blood cells (SRBCs) resulted in volume-dependent hemolysis (Figure 1)
Treatment of a 500 μL suspension of 1% SRBCs (v/v) with only 3 μL of serum resulted in measureable (p < 0.5) hemolysis, as 5.5% ± 0.9% of the SRBCs were hemolyzed
Summary
Innate immunity comprises that part of microbial defense which responds in a non-specific manner to infiltration by microbes. Serum complement is one of the first lines of defense against infection, and is made up of approximately 11 different proteins that can be activated by three different mechanisms, the classical (antibody-dependent) pathway [1], the alternative pathway [2], and the lectin-dependent pathway [3]. All three mechanisms work in a proteolytic cascade fashion, resulting in the eventual formation of a multi-protein “membrane attack complex” [4] in the outer membrane of the microbe, causing leakage of cellular contents and lysis. Serum complement is among the most important components of innate immunity, and has been identified and characterized across a broad spectrum of diverse taxa, including mammals [13] and ancient invertebrates [14,15]
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