• NK1.1+ CD4+8 T cell;
  • CD4+ bone marrow T cell;
  • Interleukin-2;
  • Interleukin-4;
  • Interferon-γ


CD4+8 or CD48+ 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+8thymocytes 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.