Early Deletion and Late Positive Selection of T‐Cells Expressing a Male‐Specific Receptor in T‐Cell ReceptorTransgenic Mice

Abstract

The ontogeny of T cells in T-cell receptor (TCR) transgenic mice, which express a transgenic αβ heterodimer, specific for the male (H-Y) antigen in association with H-2Db, was determined. The transgenic α chain was expressed on about 10% of the fetal thymocytes on day 14 of gestation. About 50% of day-15 fetal thymocytes expressed both α and β transchains and virtually all fetal thymocytes expressed the transgenicαβ heterodimer by day 17. The early expression of the transgenic TCR on CD4-8- thymocytes prevented the development of γδ cells, and led to accelerated growth of thymocytes and an earlier expression of CD4 and CD8 molecules. Up to day 17, no significant differences in T-cell development could be detected between female and male thymuses. By day 18 of gestation, the male transgenic thymus contained more CD4-8- thymocytes than the female transgenic thymus. The preponderance of CD4-8- thymocytes in the male transgenic thymus increased until birth and was a consequence of the deletion of the CD4+8+ thymocytes and their CD4-8+ precursors. By the time of birth, the male transgenic thymus contained half the number of cells as the female transgenic thymus. The deletion of autospecific precursor cells in the male transgenic mouse began only at day 18 of gestation, despite the fact that the ligand could already be detected by day 16. The preferential accumulation of CD4-8+ T cells, which expressed a high density of the transgenic TCR, occurred only after birth and was .obvious in 6-week-old female thymus. These data support the hypothesis that the positive selection of T cells expressing this transgenic heterodimer may involve two steps, i.e., the commitment of CD4+8+ thymocytes to the CD4-8+ lineage following the interaction of the transgenic TCR with restricting major histocompatibility molecules, followed by a slow conversion of CD4+8+ thymocytes into CD4-8+ T cells. In normal mice, the precursors of CD+4+8 and single positive thymocytes have the CD4-8- CD3-J11d+ (or M1/69 +) phenotype. Because of the early expression of the transgenic αβ heterodimer, this population was not detected in adult transgenic mice. All CD4-8- M1/ 69+ cells expressed the transgenic receptor associated with CD3 and could be readily grown in media containing T-cell lectins and interleukin 2.

Xenogeneic β2-Microglobulin Substitution Affects Functional Binding of MHC Class I Molecules by CD8+ T Cells

“…Thymocytes derived from h-␤ 2 m ϩ -Tg mice demonstrated reduced overall density and frequency of profiles compared with control samples. This pattern of expression is consistent with a model of enhanced negative selection (44,45), whereby only those thymocytes expressing lower TCR␤ and CD3 levels survive beyond this checkpoint (46).…”

“…1, the pattern of reduction in both the DP and SP thymocyte populations is distinct from death by neglect, which is marked by decreased SP frequency alone (44,45), as capitulated by the H-2K bϪ/Ϫ control mouse. Rather, the phenotype we have described is consistent with a negative selection model whereby high-affinity binding thymocytes are eliminated as early as the DP stage (44,45,64) and where thymocytes with lower CD3, CD8, and TCR␣␤ expression levels (Table I) are permitted to undergo maturation and expansion (44,45,46). We therefore tentatively conclude that h-␤ 2 m substitution alters the MHC-I surface that is recognized by TCR␣␤, resulting in enhanced affinity (or rigidity) of the intermolecular association and increased negative selection of thymocytes in the h-␤ 2 m-Tg mouse.…”

Concurrent visualization of trafficking, expansion, and activation of T lymphocytes and T-cell precursors in vivo

“…24 Interestingly, although we could detect DP thymocytes in the thymus of male recipients, we were unable to detect any NFAT activation. This is in agreement with previous studies showing that NFAT is not required for negative selection and suggests prompt NFAT-independent negative selection of double-positive thymocytes, which is consistent with data by Teh et al 25 To use the proposed reporter system most effectively, one has to consider the changes to the measured signals that are a function of depth. This is of particular importance when analyzing the relative signal magnitudes from reporters with differing emission spectra, as we have here.…”

Ikaros Null Mice Display Defects in T Cell Selection and CD4 versus CD8 Lineage Decisions

“…Under conditions in which the agonist peptide is absent and the selecting peptide is one that induces positive selection, as in the F5 and female H-Y TCR Tg model systems, lack of Ikaros results in the inappropriate appearance of CD4 SP thymocytes, but these cells are neither mature nor functional. Abnormally early expression of a mature ␣␤TCR at the double-negative stage, which occurs in TCR Tg mice, may potentiate the appearance of these abnormal CD4-like T cells in the Ikaros null F5 and female H-Y model systems (25,32).…”