Glucocorticosteroids modulate antigen-induced T cell apoptosis in experimental autoimmune neuritis and cause T cell proliferation in situ

Treatment of experimental autoimmune disorders of the nervous system with high doses of glucocorticosteroids (GC) or with administration of the specific antigen is effective and associated with marked T cell apoptosis in situ. Here we investigated in adoptive transfer-experimental autoimmune neuritis (AT-EAN) of the Lewis rat whether induction of T cell apoptosis resulting from T cell activation by antigen therapy can be further augmented by glucocorticosteroids (GC). AT-EAN was induced by intravenous injection of P2-specific T cell blasts. At the maximum of disease two pulses of the antigen recombinant human P2 (rhP2) were given within 12 h. Methylprednisolone was administered simultaneously or 2 h after the antigen and animals were killed 6 h after the second antigen injection. Using an in situ tailing technique followed by immunocytochemical analysis, the presence of DNA fragmentation in T lymphocytes was confirmed. The bromodeoxyuridine (BrdU) technique was employed to detect in situ proliferating cells. T cell apoptosis in sciatic nerve was enhanced after monotherapy with either antigen or GC compared to the control group receiving an irrelevant myelin protein, recombinant human P0. In combination therapy, a synergistic effect on T cell apoptosis in sciatic nerve was obtained when methylprednisolone was injected sequentially, 2 h after rhP2 protein. BrdU incorporation in the sciatic nerve as well as in the spleen, a major lymphoid organ, was significantly enhanced in animals treated with antigen followed by GC 2 h later as compared to rats receiving rhP2 only, speaking for T cell proliferation in situ associated with T cells undergoing apoptosis. Our findings underscore that different proapoptotic stimuli may act synergistically, depending on the timing of the second treatment. In this scenario even local T cell proliferation in the inflamed nervous system occurs. These results support the paradigm of antigen presentation in the nervous system.