Abstract
We investigated the possible mechanisms how interferon (IFN)‐β may control T cell infiltration in the CNS in experimental autoimmune encephalomyelitis (EAE). Adoptive transfer (AT) EAE was induced in groups of six female Lewis rats. Animals were treated with 3 × 10^5^ units of recombinant rat IFN‐β s.c. once at 18 hr, or with 10 mg/kg methylprednisolone (MP) i.v. twice at 18 and 6 hr prior to dissection, or with a combination of both. T cell apoptosis was detected by immunohistochemistry on paraffin sections of spinal cord, using morphological criteria and TUNEL staining. Double labeling of immune cells was done for tumor necrosis factor (TNF)‐α and metalloproteinase (MMP) 2. Disruption of the blood–brain barrier (BBB) was visualized by staining for albumin. In severe EAE, an increase of T cell apoptosis was seen after IFN‐β alone (all data presented as mean ± SD: 24.5% ± 2.2%, P < 0.05, vs. 19.4% ± 3.1% in controls), and in combination with MP (29.4% ± 7.3%, P < 0.05 vs. controls). Only the combination therapy decreased T cell infiltration (53.9 ± 17.7 cells/mm^2^, P < 0.05, vs. 99.5 ± 35.2 cells/mm^2^ in controls). In moderate EAE, the rate of T cell apoptosis was slightly increased after IFN‐β (21.2% ± 5.2% vs. 17.4% ± 5.0% in controls), whereas MP alone (25.5% ± 3.5%, P < 0.01 vs. controls) and the combination therapy (22.4% ± 4.8%, P < 0.05 vs. controls) had a clear augmenting effect. IFN‐β tended to decrease T cell infiltration (46.1 ± 12.7 cells/mm^2^) compared to controls (59.2 ± 18.5 cells/mm^2^). The rate of TNF‐α‐expressing T cells was significantly decreased by IFN‐β and in combination with MP. Also, TNF‐α expression in macrophages was significantly reduced by IFN‐β and by the combination therapy. The rate of MMP2‐expressing macrophages was lower after IFN‐β but clearly decreased only in combination with MP. BBB disruption was ameliorated after IFN‐β but significantly only in combination with MP. Our study indicates that IFN‐β affects the immunopathological process in EAE in several ways, but apoptosis appears as a minor component. In view of treatment of MS relapses, the synergistic effects in this study corroborate the use of a combination therapy with high‐dose MP and IFN‐β. J. Neurosci. Res. 65:59–67, 2001. © 2001 Wiley‐Liss, Inc.