LONG-LIFE SPAN OF TOLERANT T-CELLS AND THE ROLE OF ANTIGEN IN MAINTENANCE OF PERIPHERAL TOLERANCE

To follow the fate of tolerant T cells in vivo we used a transgenic mouse model in which peripheral T cell tolerance was based on a non-deletional mechanism. These mice expressed two transgenes: the MHC class I molecule K-b under the keratin IV promoter on keratinocytes (2.4 KerIV-K-b) and an anti-K-b TCR identified by the anti-clonotypic antibody Desire-1 (DES-TCR), Although these mice were tolerant to K-b skin grafts, CD8(+)DES(+) T cells were present in their lymphoid organs in the same numbers as in K-b-reactive DES-TCR single-transgenic mice. The unresponsiveness towards K-b grafts suggested previous contact of the CD8(+)DES(+) T cells with the K-b molecule on keratinocytes, but the evidence was indirect, The present study demonstrates enhanced levels of activation markers like CD44 and CD2 on the tolerant T cells, indicating contact with the K-b molecule, Continuous presence of antigen was required for maintenance of the tolerant state as shown by transfer of tolerant T cells into K-b-negative nu/nu BALB/c mice, Three days after cell transfer most recipients were still tolerant and accepted K-b-positive skin grafts, but 2 weeks after transfer the transferred cells had recovered their responsiveness and rejected K-b grafts. In order to see if contact with the tolerogen would eventually drive the tolerant cells into cell death, the life span of tolerant CD8(+)DES(+) cells was measured in thymectomized DES-TCR x 2.4 KerIV-K-b double-transgenic mice. The tolerant cells were found to have a life span of at least 8 weeks, which was comparable with the life span of non-tolerant CD8(+)DES(+) cells from DES-TCR single-transgenic mice. Thus, tolerant T cell populations can be long-lived and need continuous contact with the tolerogen to remain tolerant.