Myelin antigen-coupled splenocytes suppress experimental autoimmune encephalomyelitis in Lewis rats through a partially reversible anergy mechanism

Mechanisms of adult tolerance induced by injecting myelin Ag/ECDI (ethyl carbodiimide)-coupled splenocytes (Ag-SPL) were evaluated in Lewis rat experimental autoimmune encephalomyelitis (EAE). Rats could be tolerized against the major encephalitogenic epitope of guinea pig basic protein (Gp- BP), residues 72-89, using either S72-89-SPL or crude spinal cord homogenate (SCH)-SPL. In contrast to lymph node responses that were not affected significantly, the proliferation responses of blood T cells were markedly inhibited at the peak of EAE and during the recovery period to both Gp-BP and S72-89, but not to purified protein derivative (PPD), demonstrating Ag- specific tolerance. Tolerance induction reduced the number of infiltrating spinal cord (SC) cells, especially recruited CD45RC⁺ cells, as well as SC proliferation responses to S72-89 throughout the course of EAE. In contrast, SC response to PPD was increased at onset of EAE, but later during recovery the PPD response was also decreased compared with control rats. Tolerance induced by S72-89-SPL in blood and SC T cells could be reversed by incubation in IL-2, in accordance with an anergy model. BP-specific T cells preincubated in vitro with Gp-BP-SPL were rendered unresponsive to Gp-BP or S72-89, compared with the same T cells preincubated with histone (Hist)-SPL that remained Ag responsive. Consistent with an anergy model, preincubation with BP-SPL + IL-2 partially prevented tolerance induction to BP. T cells tolerized in vitro to BP-SPL induced milder EAE with delayed onset compared with control-tolerized T cells that produced lethal disease. These results demonstrate the efficacy of myelin Ag-coupled SPL in preventing EAE by selective tolerization of encephalitogenic T cells through a partially reversible anergy-induction mechanism.