Limiting dilution analysis of the frequency of antigen-reactive lymphocytes isolated from the central nervous system of Lewis rats with experimental allergic encephalomyelitis

Lymphocytes were isolated from the spinal cord and draining lymph nodes of Lewis rats with acute experimental allergic encephalomyelitis (EAE) 12 days after immunization with myelin basic protein (MBP) and tetanus toxoid (TT). An average of 8.0 +/- 2.0 X 10(6) cells was obtained from the spinal cord. Of these 71.1 +/- 8.6% expressed the helper-T-cell marker W3/25 and 14.8 +/- 6.2% expressed the killer/suppressor-T-cell marker OX8. By limiting dilution analysis of cells exhibiting an antigen-specific proliferative response, the average frequencies of cells reactive to MBP and TT were 3.36 +/- 2.4 and 7.60 +/- 4.1 per 10(4), respectively. In the draining lymph nodes, the frequencies of cells reactive to MBP and TT were 2.24 +/- 1.7 and 2.69 +/- 2.5 per 10(4). At a relatively early stage of clinical EAE, MBP-reactive T cells comprise only a small minority of the cells which can be isolated from the spinal cord; lymphocytes reactive to a protein antigen irrelevant to EAE pathogenesis are present in comparable numbers. This finding suggests that most of these cells accumulate as a result of mechanisms not specific for MBP-reactive lymphocytes.