The Beginning and the End of the Development of TCRγδ Cells in the Thymus

Abstract

The thymus is primarily a site for the expansion, differentiation and selection of developing cells of the TCR-αβ lineage. However, TCR-γδ cells also develop in the thymus, and are found primarily within the CD^- 8^- subpopulation (reviewed by Raulet, 1989). In our past studies (Pearse et al, 1988; Pearse et al, 1989) where we aimed to isolate subpopulations of adult mouse CD4^- 8^- thymocytes representing sequential stages of development along the TCR-αβ pathway, we have noted thymocytes with various degrees of rearrangement of TCR-γ genes, of expression of γ-mRNA, and of surface expression of TCR-γδ. Although the balance between TCR-αβ and TCR-γδ expression differed in different subpopulations, we have never found a combination of surface markers, apart form the TCR itself, which would separate the developing cells of the two lineages. The developmental pathways are intertwined, and it is not clear if there are two quite separate pathways, or if there are common streams at some stages.