Low-Dose Interleukin-2 and Regulatory T Cell Treatments Attenuate Punctate and Dynamic Mechanical Allodynia in a Mouse Model of Sciatic Nerve Injury

Purpose: Nerve injury-induced mechanical hyper-sensitivity, in particular stroking-induced dynamic allodynia, is highly debilitating and difficult to treat. Previous studies indicate that the immunosuppressive regulatory T (Treg) cells modulate the magnitude of punctate mechanical allodynia resulting from sciatic nerve injury. However, whether enhancing Treg-mediated suppression attenuates dynamic allodynia is not known. In the present study, we addressed this knowledge gap by treating mice with low-dose interleukin-2 (ld-IL2) injections or adoptive transfer of Treg cells. Methods: Female Swiss Webster mice received daily injections of ld-IL2 (1 mu g/mouse, intraperitoneally) either before or after unilateral spared nerve injury (SNI). Male C57BL/6J mice received adoptive transfer of 1 x 10(6) Treg cells 3 weeks post-SNI. The responses to punctate and dynamic mechanical stimuli on the hindpaw were monitored before and up to 4-6 weeks post-SNI. We also compared the distribution of Treg cells and CD3(+) total T cells after SNI and/or ld-IL2 treatment. Results: Ld-IL2 pretreatment in female Swiss Webster mice completely blocked the development of SNI-induced dynamic mechanical allodynia and reduced the magnitude of punctate allodynia. Delayed ld-IL2 treatment in female mice significantly attenuated the morphine-resistant punctate and dynamic allodynia at 3-5 weeks post-SNI. Adoptive transfer of Treg cells to male C57BL/6J mice 3 weeks post-SNI effectively reversed the persistent punctate and dynamic allodynia, supporting that the effect of ld-IL2 is mediated through endogenous Treg cells, and is likely independent of mouse strain and sex. Neither ld-IL2 treatment nor Treg transfer affected the basal responses to punctate or brush stimuli. Ld-IL2 significantly increased the frequency of Treg cells among total CD3(+) T cells in the injured sciatic nerves but not in the uninjured nerves or the dorsal root ganglia, suggesting the injured nerve as ld-IL2's site of action. Conclusion: Collectively, results from the present study supports Treg as a cellular target and ld-IL2 as a potential therapeutic option for nerve injury-induced persistent punctate and dynamic mechanical allodynia.

Automated summary

The study demonstrates that enhancing Treg-mediated suppression can alleviate nerve injury-induced mechanical allodynia. Treatment with ld-IL2 and adoptive transfer of Treg cells effectively improved the abnormal sensation, indicating promising therapeutic options for persistent mechanical allodynia.