Beschreibung:
<jats:p>Cortical thymic epithelial cells (c<jats:styled-content style="fixed-case">TEC</jats:styled-content>s) and medullary thymic epithelial cells (m<jats:styled-content style="fixed-case">TEC</jats:styled-content>s), which play essential roles in the establishment of a functionally competent and self‐tolerant repertoire of <jats:styled-content style="fixed-case">T</jats:styled-content> cells, are derived from common thymic epithelial progenitor cells (p<jats:styled-content style="fixed-case">TEC</jats:styled-content>s). Recent findings indicate that m<jats:styled-content style="fixed-case">TEC</jats:styled-content>s are derived from cells that express molecules that are abundant in c<jats:styled-content style="fixed-case">TEC</jats:styled-content>s rather than m<jats:styled-content style="fixed-case">TEC</jats:styled-content>s, and provide fresh insight into the characteristics of p<jats:styled-content style="fixed-case">TEC</jats:styled-content>s and their diversification pathways into <jats:styled-content style="fixed-case">TEC</jats:styled-content> subpopulations. In this issue of the <jats:italic>European Journal of Immunology</jats:italic>, Ribeiro et al. [<jats:italic>Eur. J. Immunol</jats:italic>. 2014. 44: 2918–2924] focus on <jats:styled-content style="fixed-case">CCRL</jats:styled-content>1, an atypical chemokine receptor that is highly expressed by c<jats:styled-content style="fixed-case">TEC</jats:styled-content>s rather than m<jats:styled-content style="fixed-case">TEC</jats:styled-content>s, and show that <jats:styled-content style="fixed-case">CCRL</jats:styled-content>1‐expressing embryonic <jats:styled-content style="fixed-case">TEC</jats:styled-content>s can give rise to m<jats:styled-content style="fixed-case">TEC</jats:styled-content>s. Interestingly, Ribeiro et al. further report that a fraction of postnatal m<jats:styled-content style="fixed-case">TEC</jats:styled-content>s express <jats:styled-content style="fixed-case">CCRL</jats:styled-content>1 at a low level, suggesting novel complexity in m<jats:styled-content style="fixed-case">TEC</jats:styled-content>s.</jats:p>