IN-VITRO NEGATIVE SELECTION OF ALPHA-BETA-T-CELL RECEPTOR TRANSGENIC THYMOCYTES BY CONDITIONALLY IMMORTALIZED THYMIC CORTICAL EPITHELIAL-CELL LINES AND DENDRITIC CELLS

We have established conditionally immortalized thymic cortical epithel ial cell lines from transgenic mice carrying a temperature-sensitive S V40 large T antigen. One of these cell lines expresses cortical marker s and produces IL-1alpha, IL-6, IL-7, and TGF-beta1. These cells expre ss class I major histocompatibility complex (MHC) constitutively and c lass II MHC upon induction with IFN-gamma. The cells appear to have a normal class I antigen presenting pathway since messages for both pept ide transporter genes (TAP1, TAP2) were detected. The ability of these cortical epithelial cells to present peptide antigen was compared to that of thymic dendritic cells. In suspension culture with alphabeta T cell receptor (TcR) transgenic thymocytes, these epithelial cells and dendritic cells (pre-pulsed with peptide cognate for the transgenic T cR) caused down-regulation of CD4, CD8, and TcR in an antigen dose-dep endent and MHC-restricted manner. CD4(dull)CD8dull cells were taken as evidence for negative selection because these cells contained apoptot ic DNA. Concentration of peptide required for negative selection of th ymocytes was similar between dendritic cells and cortical epithelial c ells. In contrast, alphabetaTcR transgenic spleen cells were activated only by dendritic cells but not by cortical epithelial cells.