Sequential expression of transforming growth factor-β1 by T-cells, macrophages, and microglia in rat spinal cord during autoimmune inflammation

Transforming growth factor-beta 1 (TGF-beta 1) is crucially involved in regulating inflammatory events during experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. Despite accumulating evidence for local expression of TGF-beta 1 in the inflamed nervous system, uncertainty remains regarding its cellular source. We have investigated the temporospatial distribution of TGF-beta 1 gene expression in rat spinal cord during EAE. In actively induced EAE, in situ hybridization revealed strong expression of TGF-beta 1 in meningeal and perivascular mononuclear infiltrates at onset of the disease, continued expression in perivascular infiltrates and scattered mononuclear cells at maximal disease severity, and expression in scattered parenchymal cells during recovery. Double labeling studies revealed subpopulations of infiltrating T-cells to be the major source of TGF-beta 1 early in the disease, followed by macrophages at peak severity and microglial cells during the recovery phase of EAE. Astrocytes and neurons did not express TGF-beta 1. Quantification of mRNA by Northern blot analysis revealed that cellular expression of TGF-beta 1 by T-cells, macrophages, and microglia sums up to a long-lasting elevation of TGF-beta 1 mRNA extending well into the recovery phase. Our data indicate cellular diversity and suggest functional diversity of TGF-beta 1 gene expression during EAE. While TGF-beta 1 expressed early in the disease by T-cells may contribute to inflammatory lesion development, microglial cells may potentially contribute to recovery by expressing immunosuppressive TGF-beta 1 during remission.