Involvement of the interleukin 4 pathway in the generation of functional γδT cells from human pro-T cells

We have used the technique of in situ hybridization to investigate the transcription of genes encoding the CD3 complex and the lymphokine interleukin 4 (IL-4) by human pro-T cells-i.e., cells that phenotypically resemble those T-cell precursors that colonize the thymus during early intrathymic development. CD1^-2^-3^-4^-7⁺8 ^-45⁺ pro-T cells isolated from postnatal thymi via immunoselection with a panel of specific monoclonal antibodies are already committed to the T-cell lineage because most of them transcribe the genes encoding the δ and ε chains of the CD3 complex. About half of such pro-T cells synthesize IL-4 mRNA in the absence of any exogenous stimulation. Upon culture with IL-4, pro-T cells extensively proliferate and differentiate into functionally competent, mature γδ T cells expressing a T-cell receptor repertoire similar to that of γδ T cells that can be found in postnatal thymus. The IL-4 response of pro-T cells is not mediated by induction of the interleukin 2 (IL-2)-IL-2 receptor pathway and, unlike IL-2-driven T-cell differentiation, does not require the presence of stromal cells. Taken altogether, these findings suggest that an autocrine IL-4-mediated pathway might be implicated in early thymocyte differentiation - namely, in the generation of T cells bearing the γδ T-cell receptor.