A T cell clone with three potential TCR α chain rearrangements expresses only one receptor combination at the cell surface

In determining the T cell receptor (TcR) usage of various T cell clones that recognize peptide antigens derived from allergens, a particular clone (AC20) was found, that apparently expressed three different species of mRNA encoding α chains. The logical conclusion that the cells were not clonal was refuted by the finding of only a single β chain rearrangement. One of the α chains (Vα20), was not in frame, but two Vα8 transcripts of different lengths were both potentially translatable. Sequence analysis suggested that the shorter transcript was generated by a secondary splice event from the longer, through the use of a splice donor sequence encoded by the Jα38 gene segment. The efficiency of excision of the intervening sequence is such that approximately equal amounts of the long and short transcripts occur in the steady state pool of mRNA. This phenomenon has been reported previously in TcR α rearrangements, but it has never been made clear whether these truncated chains can form a functional TcR. Reconstitution of a TcR negative cell line with these transcripts showed that only the full length α chain was able to pair efficiently with the β chain to generate a functional receptor at the cell surface.