NK1.1+ CD4+ CD8‐ thymocytes with specific lymphokine secretion

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Abstract
CD4+8− or CD4−8+ thymocytes have been regarded as direct progenitors of peripheral T cells. However, recently, we have found a novel NK1.1+ subpopulation with skewed T cell antigen receptor (TcR) Vβ family among heat‐stable antigen negative (HSA−) CD4+8− thymocytes. In the present study, we show that these NK1.1+ CD4+8− thymocytes, which represent a different lineage from the major NK1.1− CD4+8− thymocytes or CD4+ lymph node T cells, vigorously secrete interleukin (IL)‐4 and interfron (IFN)‐γ upon stimulation with immobilized anti‐TcR‐αβ antibody. On the other hand, neither NK1.1− CD4+8−thymocytes nor CD4+ lymph node T cells produced substantial amounts of these lymphokines. A similar pattern of lymphokine secretion was observed with the NK1.1+ CD4+ T cells obtained from bone marrow. The present findings elucidate the recent observations that HSA− CD4+8− thymocytes secrete a variety of lymphokines including IFN‐γ, IL‐4, IL‐5 and IL‐10 before the CD4+8− thymocytes are exported from thymus. Our evidence indicates that NK1.1+ CD4+8− thymocytes are totally responsible for the specific lymphokine secretions observed in the HSA‐ CD4+8− thymocytes.