Alterations during positive selection in the thymus of nackt CD4-deficientmice

The T-cell repertoire is shaped by the positive and negative selection of i mmature CD4(+) CD8(+) double positive (DP) thymocytes. Positive selection o f DP T cells to the CD4(+) CD8(-) and CD4(-) CD8(+) simple positive (SP) li neages is a multistep process which involves cellular interactions between thymocytes and stromal cells. Mutant nackt (nkt/nkt) mice have been shown t o have a deficiency in the CD4(+) CD8(-) T-cell subset both in the thymus a nd in the periphery. The present report suggests that nkt/nkt mice present alterations in early steps of positive selection because they show decrease s in the percentages of CD69(+) and CD5(+) cells within the DP subset. Expe riments involving bone marrow transfer and thymic chimeras demonstrate that the thymic epithelium of nkt/nkt mice is involved in the alterations regis tered during positive selection and dictates the ultimate fate of CD4(+) SP cells.