The CD11b-diphtheria toxin receptor (DTR) mouse has been widely used to study the role of microglia and macrophages in disease. By taking advantage of the insensitivity of murine cells to diphtheria toxin (DT), transgenic expression of the DTR renders CD11b-expressing cells DT sensitive, leading to toxin-induced apoptosis. Despite use of these mice across the literature, we found DT treatment caused high mortality and behavioural deficits in naive CD11b-DTR and wild-type mice, highlighting the need for DTR mouse line characterisation and consideration of potential side-effects, before use in disease models.

In this study, CD11b-DTR and C57BL/6 mice were implanted with a cannula into the lateral ventricles and allowed to recover for two-weeks. Mice were then infused with differing doses of DT for up to 10 days. Throughout the treatment period, mice underwent the open field test, rotarod and Y-maze to assess motor function and memory. Blood testing and histological analysis are being conducted, and CD11b depletion efficiency in the transgenic mice will be quantified in the midbrain, striatum and hippocampus.

We found CD11b-DTR mortality sensitive to all doses of DT, and observed dose-dependent survival in wild-type mice. Unexpectedly, wild-type DT treated mice exhibited severe loss of motor function and mild impairment of memory, and DT severely affected CD11b-DTR mice performance across all doses in the Y-maze and rotarod. Taken together, our results suggest possible shortcomings of the DT-mediated ablation system as wild-type mice are non-specifically effected by DT, reiterating the importance of employing appropriate controls in studies using transgenic DTR mice.