International Immunology, Vol. 6, No. 2, pp. 277-287 © 1994 Oxford University Press Induction of tolerance to self MHC class I molecules expressed under the control of milk protein or /3-globin gene promoters Anne-Martt Sponaas, Peter D. Tomlinson, Jane Antonlou, Nathalie Auphan 1 , Clair Langler, Bernard Malissen 1 , Anne-Marie Schmttt-Verhulst 1 , and Andrew L. Mellor Division of Molecular Immunology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK 1 Centre d'lmmunologie de Marseille-Luminy, CASE 906, 13288, Marseille, Cedex 9, France Key words: T cells, tolerance, transgenic mice Abstract We have studied tolerance Induction In transgenic CBA mice expressing H-2K" genes under the Influence of guinea-pig o-lactalbumln (KAL) or human /3-globln gene promoter (K/3). KAL radlo- reslstant cells, but not bone marrow derived cells, Induce tolerance to H-2K" In chlmerlc mice. In contrast, bone marrow derived and radio-resistant cells of KjS mice Induce tolerance. Although appropriate, tissue-specific, expression of H-2K b molecules occurs In KAL and K/S mice, H-2K" Is expressed at low levels In thymus of transgenic mice. In addition, dendritic cells and macrophages express H-2K b molecules when K/3, but not when KAL bone marrow Is cultured In vitro. The mode of tolerance induction was examined In double transgenic mice by mating KAL or K/9 mice to mice expressing TCR transgenes (Tg-TCR) derived from a H-2K b specific, CD8-independent cytotoxlc T cell clone. In both cases, a large number of Tg-TCR + CD8+CD4+ thymocytes develop but mature CD8+CO4" thymocytes fall to appear suggesting that thymocytes are eliminated late In development. Some CD8-CD4- and CD8-CD4+ Tg~TCR + T cells develop In double transgenic mice and respond to activation through their TCR - CD3 complex In vitro, although no responses to stimulation with H-2K b expressing cells were detected. Thus, tolerance Induction In KAL and K0 mice proceeds via a deletlonal mechanism that Is Inefficient due either to low numbers of H-2K b expressing thymtc cells or to the low levels of H-2K b expressed by thymlc cells, or to a combination of these factors. Introduction Clonal elimination of immature thymocytes is an important, but not the sole, mechanism by which a state of tolerance to self molecules is acquired in the T cell repertoire of every individual (1 - 4). However, many self proteins are not expressed constitutivery by all cells. Indeed, some self proteins are expressed only by cells in the peripheral, extra-thyme compartment. One factor likely to influence the way in which tolerance is induced and, consequently, the plasticity and persistence of the tolerant state and the associated risk of developing autoimmunity, is the type and number of cells able to present self molecules (as complexes between self MHC and processed self peptides) to thymocytes as they differentiate and mature. Cells derived from bone marrow stem cells are potent mediators of clonal elimination (negative selection) as demonstrated by experiments carried out in vivo (5). In particular, dendritic cells are efficient mediators of thymocyte deletion in vitro (6,7) and in vivo (7). Thymic epithefial ceBs are also able to effect negative (6,8,9) and positive (10) selection of thymocytes. The relative efficacy by which these, and other types of cell such as thymocytes, are able to induce tolerance via clonal elimination in the thymus is not clear but there are reports that thymocytes are able to effect clonal elimination in vitro (11) and in vivo (12) as well as positive selection in vivo (13). A number of groups (4,8) have addressed these issues using transgenic mice carrying recombinant MHC genes linked to heterdogous, cell type and/or tissue specific transcriptional promoters as a means of mimicking this situation. From studies in which MHC class I transgenes have been used, it is clear that clonal elimination can occur early in thymocyte maturation, at the CD8 + CD4 + stage (2,3), or at the later CD8+CD4" stage (14). Correspondence to: A. L. Mellor Transmitting editor: A. Cooke Received 5 July 1993, accepted 22 October 1993 at Universite D'Aix-Marseille on January 16, 2015 http://intimm.oxfordjournals.org/ Downloaded from