Diversity of T cell receptor delta-chain cDNA in the thymus of a one-month-old pig.

Pig TCR delta-chain cDNA sequences were obtained from the anchored PCR products of the reverse-transcribed RNA from the thymus of a 1-mo-old germfree pig. Among 43 sequences analyzed, 4 different J delta sequences were found, and in the cDNA sequences of rearranged V-D-J junctional regions, three putative D delta sequences were assigned. Also, the V delta region sequences were grouped into five families. One family, V delta 1, consisted of a large number of members and the other families consisted of limited members as determined by cDNA sequences as well as genomic Southern blots. Using PCR, V delta 1 gene segments were also obtained from liver genomic DNA of the same individual pig. Thirty-one distinct sequences were found for the V delta 1 family including the sequences obtained from both the thymic RNA and the PCR product of liver DNA. All the V delta 1 genes were found to be associated with almost identical leader gene sequences. The amino acid sequences of the complimentarity-determining region 3 coded by the V-D-J joints gave long and variable lengths with a high content of tryptophan and charged amino acids. The length of the complimentarity-determining region 3 in the porcine TCR delta-chain supports the idea that TCR delta-chain is designed to see Ags directly similar to the Ig heavy chain. Data presented from this study shows that the porcine TCR delta-chain has extensive V region diversity as well as junctional diversity. The combination of these two creates a level of diversity that is the highest of any lymphocyte Ag receptor studied so far.

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