Immunosuppressive effect of cyclosporin A in two lymphocyte transfer models in rats: comparison of in vivo and in vitro treatment.

The immunosuppressive effect of CS-A was first studied in the assay for local GvHR. 3 X 10(6) viable spleen cells from LEW rats were injected into one foot pad of LEW X BN hybrids and both PLN were weighed 7 days later. Treatment of the recipients with 3 doses of 50 mg/kg/day of CS-A suppressed this local GvHR. The effect was more pronounced when treatment started at the time of cell transfer rather than a few days before peak response. In vitro incubation of the cellular inoculum with CS-A also prevented local GvHR. Histology of the PLN confirmed the quantitative results expressed by the PLN index. CS-A was further investigated in the EAE model in LEW rats. It protected rats sensitised with spinal cord emulsified in complete Freund's adjuvant for as long as they were treated with CS-A. Treatment delayed until after the appearance of EAE also markedly improved their condition. Oral treatment of recipients with 50 mg/kg/day CS-A prevented the development of adoptive EAE following the transfer of lymphoid cells conditioned in vitro. The presence of 0.1-1.0 microgram CS-A in the medium of the sensitised lymphoid cells also inhibited the adoptive transfer of EAE. Finally, if the cells for the adoptive transfer were derived from CS-A-treated sensitised donors, they failed to induce EAE. Histological examination supported the symptomatic findings.