Analysis of T cell receptor β chains in Lewis rats with experimental allergic encephalomyelitis: Conserved complementarity determining region 3

This study explores the usage of T cell antigen receptor (TCR) β chain elements in Lewis rats with experimentally induced allergic encephalomyelitis (EAE). TCRs from 15 different T cell clones and hybridomas derived from animals immunized with myelin basic protein (MBP), and all having specificity for the 21-mer encephalitogenic fragment MBP 68-88, utilized Vβ8.2. In addition, there was a marked conservation of the first two amino acid residues of the junctional complementarity determining region 3 (CDR3) associated with the V/38.2 receptors. 12 of 15 contained an aspartic acid followed by serine regardless of the associated Jβ element. At the nucleotide level, this conservation of AspSer residues was accomplished with few or no nongermline-encoded nucleotide (N) additions. A similar pattern of AspSer usage and N region nucleotide additions was observed in a number of Vβ8.2 isolates derived from MBP-immunized lymph nodes. In contrast, Vβ8.2 polymerase chain reaction amplified isolates from Lewis T cells activated with concanavalin A or from lymph nodes of complete Freund's adjuvant-immunized animals showed no AspSer utilization (0/31) in the CDR3, and four to nine N region nucleotide additions. We conclude from this finding that AspSer residues in the CDR3, limited N region nucleotide additions, along with Vβ8.2 sequences, contribute to TCR specificity for MBP 68-88. This raises the possibility that encephalitogenic, disease-causing T cells either represent a population that derives from late fetal life or alternatively, that they are rare cells with this particular TCR phenotype contributed to the T cell pool throughout adulthood and are selected by antigen. In either case, the CDR3 AspSer sequences as well as Vβ8.2 sequences are candidates for the receptor target structures recognized by regulator T cells in recovery from and resistance to active EAE. In this respect, a preliminary analysis of TCR utilization in three T cell clones specific for MBP 68-88 isolated from animals recovered from active EAE indicates that while all three use Vβ8.2, only one contains AspSer in the CDR3.