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Science 31 January 1997:
Vol. 275. no. 5300, pp. 595 - 0
DOI: 10.1126/science.275.5300.595h
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As T cells mature in the thymus, their receptors are biased against self-peptides (negative selection) but also toward nonself peptides. How does this latter positive-selection process prepare the T cell repertoire for encounters with the huge array of nonself sequences? Nakano et al. (p. 678) explored this question by studying mice that were injected in the thymus with an adenovirus vector expressing a nonself peptide along with an invariant chain (Ii) of the class II major histocompatibility complex. In this way, the peptide was expressed near its binding groove. Although the T cells could respond to both closely related and unrelated peptide sequences, the particular repertoire changed with even slight changes to the original peptide sequence.




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