Pidotimod alleviated experimental autoimmune encephalomyelitis by regulating the balance of splenic lymphocytes.

Objective: To examine whether pidotimod affects the progression and severity of experimental autoimmune encephalomyelitis (EAE), a classic animal model of multiple sclerosis (MS), the balance of splenic lymphocytes in pidotimod-treated and untreated EAE mice was examined.

Methods: C57BL/6J mice were immunized by subcutaneous injection of an emulsion containing MOG35-55, with subsequent monitoring of their general condition and clinical scores following treatment with pidotimod or saline solution (vehicle control). Hematoxylin and eosin (H&E) staining, along with flow cytometry (FCM), was employed to evaluate leukocyte infiltration, while FluoroMyelin™ Green staining was utilized to assess axonal demyelination in the central nervous system (CNS). Additionally, FCM was conducted to investigate the effects of pidotimod on splenic lymphocytes both in vitro and in vivo during the peak stage of EAE.

Results: Compared to the vehicle control, pidotimod treatment significantly reduced the clinical scores, decreased leukocyte infiltration in the spinal cord and brain, and suppressed demyelination in the spinal cord. Furthermore, pidotimod treatment markedly increased the populations of CD4⁺ CD25⁺ Foxp3⁺ regulatory T cells (Tregs) and CD8⁺ Foxp3⁺ Tregs, while decreasing the numbers of CD4⁺ IFN-γ⁺ helper T cells (Th1), CD4⁺ IL-17⁺ helper T cells (Th17), and CD8⁺ IL-17⁺ cytotoxic T cells (Tc17) in the spleen during the peak stage of EAE both in vitro and in vivo. Additionally, pidotimod treatment significantly diminished the population of B220⁺ TNF-α⁺ B cells in the spleen at the peak stage of EAE both in vitro and in vivo.

Conclusions: The present study preliminarily explored the effects and potential immunomodulator mechanisms of pidotimod in treating EAE mice. Results indicated that pidotimod treatment decreased the percentages of CD4⁺ IFN-γ⁺ Th1 cells, CD4⁺ IL-17⁺ Th17 cells, CD8⁺ IL-17⁺ Tc17 cells and B220⁺ TNF-α⁺ B cells, while increasing the percentages of CD4⁺ CD25⁺ Foxp3⁺ Tregs and CD8⁺ Foxp3⁺ Tregs in the spleen at the peak stage of EAE. Additionally, pidotimod reduced leukocyte infiltration into the spinal cord and brain, as well as demyelination in the spinal cord. These findings suggest that the neuroprotective effects of pidotimod in EAE mice may be its ability to regulate the balance of splenic lymphocytes.