UNTRANSFECTED AND SV40-TRANSFECTED FETAL AND POSTNATAL HUMAN THYMIC STROMAL CELLS - ANALYSIS OF PHENOTYPE, CYTOKINE GENE-EXPRESSION AND CYTOKINE PRODUCTION

The thymic stromal network is complex and heterogeneous, containing th ymic epithelial cells which are thought to play an important role duri ng T-celt development and thymic fibroblasts which role is less define d. We herein present a phenotypic and functional comparison between de fined thymic stromal cell populations. We transfected SV40 ori- into f etal and postnatal thymic stromal cell cultures and obtained SV40-immo rtalized clones of epithelial and fibroblastic nature as demonstrated by expression of intracellular keratin. These various clones were char acterized in detail and compared to their untransfected bulk culture c ounterparts for phenotype, cytokine gene expression and cytokine produ ction. All the different thymic stromal cells examined, constitutively expressed ICAM-1, LFA-3, MHC class I antigens, CD44, and the genes co ding for IL-7, SCF and TGF-beta, but not TNF-alpha. After IL-1 stimula tion, epithelial cells seemed to produce more GM-CSF than fibroblasts, and that trend was also seen for IL-6 secretion. SV40 cells were also regulated by IFN-gamma which induced MHC class II antigens and inhibi ted the IL-1 induced GM-CSF production. SV40 cells differed from their untransfected counterparts by an atypical expression of CD40 and lack ed constitutive IL-1alpha gene expression. We isolated clones with dis tinct properties, 24SV48, a highly proliferative CD34 positive TEC sec reting low levels of GM-CSF and lacking constitutive IL-1alpha and bet a gene expression, and CTISV93, an epithelial clone of postnatal origi n with a high IL-1-induced cytokine production. In spite of difference s with untransfected bulk cultures, the various SV40 immortalized clon es may represent useful tools to further study the human thymic stroma .