Sterile bred rats for studies involving septic challenges have differing levels of endogenous immunity to endotoxin core

Abstract

Background Low levels of natural endogenous antibody to endotoxin core (EndoCAb) have been related to poor outcome after surgery1 2 and sepsis.3 Rats are often used in animal models of sepsis, but baseline EndoCAb status, which varies greatly in humans, is rarely determined in these animals. The aim of this study was to determine if any significant differences existed between laboratory rats in baseline endotoxin immunity. Method: 35 sterile bred Wistar rats were anaesthetised with Isoflurane and blood 1 ml was removed by aseptic technique via cardiac puncture. This blood was then centrifuged at 2000g for 10 min and serum separated. The serum was diluted 1:200 and 100 μl added to the ELISA wells which were pre-coated with a variety of core moieties of endotoxin. This was then incubated at 37°C for 1 h, washed and 1:500 alkaline phosphatase anti-rat IgG 100 μl added. After further incubation and washing, alkaline phosphatase substrate was added. This was left at room temperature until the colour developed to give a maximum optical density of approximately 2.0 at the top of the standard curve using an ELISA plate reader. Results: These are shown in Figure 4. Conclusions This demonstrates that in animal experiments where there is supposed uniformity in a sterile bred population there remain vast differences in their underlying immunity to endotoxin which may affect the response to a septic challenge.