Lymphokine-mediated induction of antigen-presenting ability in thymic stromal cells

Abstract

We have established and characterized long term thymic stromal cultures from BALB/c (H-2d) and CBA/J (H-2k) mice. All cultures contained multiple adherent cell types, whereas some also contained thymic macrophages (TM). Culture supernatants from all cultures tested contained macrophage colony-stimulating factor activity, whereas only cultures with TM had soluble or membrane-associated interleukin (IL)-1. However, a thymic epithelial cell line (3D . 1), cloned from one of these cultures, produced IL-1 bioactivity. Further analysis confirmed the production of IL-1 alpha mRNA by the epithelial cell. No IL-2 or IL-4 (formerly called B cell stimulatory factor 1) activity was detected in any of the cultures. Antigen-presenting (AP) ability was determined using the chicken ovalbumin (OVA)-specific, I-Ad-restricted T cell hybridoma 3DO-18.3. Harvested TM exhibited antigen-specific, Ia-restricted AP ability which was enhanced by IL-4 as well as interferon-gamma (IFN-gamma). In contrast, AP ability was detected in non-macrophage stromal cell cultures (NMSC) only after preincubation with IFN-gamma. AP by preinduced NMSC was also Ia-restricted and could be blocked by anti-I-Ad antibodies. Since the T cell receptor of 3DO-18.3 is known to recognize a peptide produced by CNBr degradation of OVA, these observations suggest that both TM and NMSC can process OVA to produce this peptide. Glutaraldehyde-fixation experiments confirmed that NMSC must process native OVA into antigenic peptides for successful AP. Assays using several cloned stromal cell lines of different lineages suggested that only epithelial cells could be induced with IFN-gamma to exhibit competent AP. Given the possible role for IFN-gamma in the maintenance of Ia in the thymus, we investigated whether IFN-gamma production could be ascribed to a subpopulation of thymocytes. Culture supernatants from calcium ionophore and phorbol ester-stimulated peanut agglutinin-negative, but not peanut agglutinin-positive, thymocytes induced AP ability in NMSC. Thus, some thymocytes can produce an Ia-inducing lymphokine (most likely IFN-gamma) which may play an important role in T cell ontogeny through its effects on both thymic macrophages and thymic epithelial cells.