Recently, we reported that thymocytes expressing the CD8 molecule on their surface can give rise to CD4+CD8+ double‐positive and CD4+ single‐positive progeny following intrathymic transfer into an irradiated host mouse. Thymcoytes expressing a high density of CD8, referred to as CD8hi, and those expressing a low density of the molecule, CD8lo, were both able to differentiate in vivo. In this study we examined the ability of these CD8+ thymocyte populations and of CD4−CD8− double‐negative thymocytes to change their phenotype during brief in vitro culture. CD8− thymocytes were prepared by anti‐CD4 plus complement lysis followed by positive selection of the survivors on anti‐CD8‐coated plates. After 16 h of culture, > 60% of CD8+ thymocytes became double‐positive. Both CD8hi and CD8lo cells were able to show this in vitro change: about 30% of the former and about 80% of the latter became double‐positive. In contrast to this, double‐negative thymocytes which had been depleted of cells expressing low densities of CD8 did not show such a phenotypic conversion in vitro. Further panning experiments suggested that all of the CD8+ thymocytes actually express a low surface density of the CD4 molecule which is undetectable in our cytofluorometric assays.
ASJC Scopus subject areas
- Immunology and Allergy