CONSTITUTIVE EXPRESSION OF INTERLEUKIN-7 MESSENGER-RNA AND PRODUCTION OF IL-7 BY A CLONED MURINE THYMIC STROMAL CELL-LINE

Mouse interleukin-7 (IL-7) cDNA was cloned from mouse thymic stromal cell clone MRL104.8a using a polymerase chain reaction (PCR) technique and expressed in COS-7 cells. The resulting recombinant interleukin-7 (rIL-7) supported the proliferation of mouse antigen-specific helper T cell (Th) clone 9-16 in the absence of IL-2 and antigen as well as mouse pre-B cell line DW34. It was also found that high levels of the mRNA for IL-7 were constitutively expressed in the MRL 104.8a cells, and a potent amount of IL-7 was produced in its culture supernatant. These results provide the evidence for constitutive expression of IL-7 mRNA and for production of IL-7 by thymic stromal cells that have a critical role in intrathymic T cell development. The results are discussed in the context of the functional and molecular relationship between IL-7 and the previously described cytokines produced by thymic stromal cells.