PHENOTYPICALLY DIVERSE MOUSE THYMIC STROMAL CELL-LINES WHICH INDUCE PROLIFERATION AND DIFFERENTIATION OF HEMATOPOIETIC-CELLS

The heterogeneity of the thymic stroma has made careful characterizati on of particular thymic stromal cell types difficult. To this end, we have derived a panel of cloned thymic stromal cell lines from simian v irus 40 T antigen (SV40-T antigen) transgenic mice. Based on their ana lysis with monoclonal antibodies that distinguish among subsets of thy mic stroma cells, and on the morphology and ultrastructural features o f the different clones, we suggest that our panel includes representat ives of the thymic subcapsular cortex or thymic nurse cells (427.1), t he deep cortex or cortical reticular cells (1308.1) and the medulla in cluding medullary interdigitating (IDC)-like cells (6.1.1) and medulla ry epithelial cells (6.1.7). A fifth cell type of undesignated but app arent medullary origin (6.1.11) was also isolated. All of the cell lin es constitutively express the SV40 T antigen transgene and the class I antigens of the major histocompatibility complex (MHC), and they can be induced to express MHC class II antigens upon stimulation with reco mbinant interferon-gamma (IFN-gamma). These cell lines elaborate a fac tor(s) that induces the proliferation of cells from the fetal liver an d bone marrow, but not from the neonatal thymus. A factor(s) elaborate d by the 1308.1 cell line also induces the proliferation of fetal thym ocytes in the absence of mitogens, phorbol esters or calcium ionophore which is augmented with the addition of recombinant interleukin-2 (IL -2). Analysis by reverse transcription polymerase chain reaction with primers for some mouse cytokines reveals that each of these cell lines contain granulocyte-macrophage colony-stimulating factor (GM-CSF) tra nscripts and that 1308.1, 6.1.1 and 6.1.7 produce IL-6 mRNA. Cell line s 1308.1 and 6.1.1 also produce IL-7; 6.1.1 produces IL-1beta and tumo r necrosis factor (TNF)-alpha while the 427.1 cell line produces IL-5 and IFN-gamma mRNA. None of the cell lines tested express the IL-2 rec eptor, IL-2, IL-3, IL-4, TNF-beta or macrophage inflammatory proteins mRNA. Conditioned medium (CM) from 1308.1 and 6.1.11 induced different iation of cells purified from the mouse fetal liver into granulocytes; 1308.1 CM also induced differentiation of the mouse hematopoietic ste m cell line 32DCl3(G) suggesting that the CM contains granulocyte (G)- CSF activity. Each cell line produces GM-CSF but the greatest activity is associated with 1308.1 and 6.1.11 CM. The availability of these we ll-characterized, functional, cloned thymic stromal cells will allow a more detailed analysis of the role of each cell type in both myeloid and T cell development.