Supplementary Material for: A Promising New Approach for the Treatment of Inflammatory Pain: Transfer of Stem Cell-Derived Tyrosine Hydroxylase-Positive Cells

Objectives: The appearance of endogenous tyrosine hydroxylase-positive cells (TH⁺ cells) in collagen-induced arthritis was associated with an anti-inflammatory effect. Here we investigated putative anti-inflammatory and antinociceptive effects of the transfer of induced, bone marrow stem cell-derived TH⁺ cells (iTH⁺ cells) on murine antigen-induced arthritis (AIA). Methods: Bone marrow-derived stem cells were differentiated into iTH⁺ cells. These cells were transferred to mice immunized against methylated bovine serum albumin (mBSA) 2 days before AIA was induced by injection of mBSA into one knee joint. In AIA control mice and iTH⁺-treated mice the severity of AIA, pain-related behavior, humoral and cellular responses, and the invasion of macrophages into the dorsal root ganglia were assessed. Results: The intravenous transfer of iTH⁺ cells before AIA induction did not cause a sustained suppression of AIA severity but significantly reduced inflammation-evoked pain-related behavior. The iTH⁺ cells used for transfer exhibited enormous production of interleukin-4. A major difference between AIA control mice and iTH⁺-treated AIA mice was a massive invasion of the dorsal root ganglia by iNOS-negative, arginine 1-positive macrophages corresponding to an M2 phenotype. The differences in other cellular and humoral immune parameters such as release of cytokines from stimulated lymphocytes between AIA control mice and iTH⁺-treated mice were small. Conclusions: The transfer of iTH⁺ cells may cause a long-lasting reduction of arthritis-induced pain even if it does not ameliorate inflammation. The invasion of M2 macrophages into the dorsal root ganglia is likely to be an important mechanism of antinociception.