Positive selection of gamma delta T cells.

The issue of T-cell repertoire selection has been addressed recently by several laboratories. While evidence has been provided for both negative and positive selection of CD4+ and CD8+ alpha beta T cells, the molecular basis of positive selection remains unclear. In this article Juan Lafaille and colleagues describe molecular features of gamma delta T-cell selection in the fetal thymus. These features were deduced from extensive junctional sequence data of gamma delta T-cell receptor genes in fetal thymocytes. Their data suggest the active participation of a self peptide in the positive selection of gamma delta T cells.