Apoptosis of V beta 8.2+ T lymphocytes in the spinal cord during recovery from experimental autoimmune encephalomyelitis induced in Lewis rats by inoculation with myelin basic protein.

To study T cell apoptosis during spontaneous recovery from experimental autoimmune encephalomyelitis (EAE), we extracted lymphocytes from the spinal cords of Lewis rats with EAE induced by inoculation with myelin basic protein (MBP) and adjuvants. Using flow cytometry we assessed the numbers of CD5+ and TCR alpha beta + lymphocytes, as well as V beta 8.2+ lymphocytes, which constitute the predominant encephalitogenic MBP-reactive cells in Lewis rats. Rats developed neurological signs of disease 10-12 days after inoculation. The peak of disease was on day 14 after inoculation and was followed by clinical recovery. The numbers of CD5+, TCR alpha beta + and V beta 8.2+ cells obtained from the spinal cord were greatest on day 13. During spontaneous clinical recovery, there was a decline in the numbers of all the cells studied, with a selective loss of V beta 8.2+ cells from the CD5+ and TCR alpha beta + populations. To determine whether the decline in lymphocyte numbers was due to apoptosis, we used simultaneous surface labelling and propidium iodide staining of the DNA of the cells extracted from the spinal cord. From day 14 onwards, there was selective enrichment of V beta 8.2+ cells in the apoptotic population, and the percentage of V beta 8.2+ cells undergoing apoptosis was greater than the percentages of CD5+ and TCR alpha beta + cells undergoing apoptosis. These findings indicate that recovery from acute EAE is associated with the selective apoptosis, in the central nervous system, of these disease-relevant cells. The findings in this study of actively induced EAE are similar to those of our previous study of EAE induced by transfer of encephalitogenic MBP-specific T cells (Z. Tabi et al., Eur. J. Immunol. 24: 2609-2617, 1994) and further support the hypothesis that selective apoptosis of autoreactive T cells in the central nervous system is of primary importance in spontaneous recovery from EAE.