Cross-Positive Selection of Thymocytes Expressing a Single TCR by Multiple Major Histocompatibility Complex Molecules of Both Classes: Implications for CD4+ versus CD8+ Lineage Commitment

Abstract

This study has investigated the cross-reactivity upon thymic selection of thymocytes expressing transgenic TCR derived from a murine CD8+ CTL clone. The Idhigh+ cells in this transgenic mouse had been previously shown to mature through positive selection by class I MHC, Dq or Lq molecule. By investigating on various strains, we found that the transgenic TCR cross-reacts with three different MHCs, resulting in positive or negative selection. Interestingly, in the TCR-transgenic mice of H-2q background, mature Idhigh+ T cells appeared among both CD4+ and CD8+ subsets in periphery, even in the absence of RAG-2 gene. When examined on β2-microglobulin−/− background, CD4+, but not CD8+, Idhigh+ T cells developed, suggesting that maturation of CD8+ and CD4+ Idhigh+ cells was MHC class I (Dq/Lq) and class II (I-Aq) dependent, respectively. These results indicated that this TCR-transgenic mouse of H-2q background contains both classes of selecting MHC ligands for the transgenic TCR simultaneously. Further genetic analyses altering the gene dosage and combinations of selecting MHCs suggested novel asymmetric effects of class I and class II MHC on the positive selection of thymocytes. Implications of these observations in CD4+/CD8+ lineage commitment are discussed.

TCR-MHC docking orientation: natural selection, or thymic selection?

“…Thus, any bias that may be present is not likely to result from conserved MHC contacts, but rather from other forces, such as TCRa/b chain pairing preferences. The fact that T cells expressing transgenic TCRs can be selected on a variety of MHC allotypes, including different MHCI and MHCII alleles [46], suggests that if a TCR exhibits a binding preference for one MHC, that preference cannot trump T cell selection on other alleles.…”

Ectopic expression of a T-box transcription factor, eomesodermin, renders CD4+ Th cells cytotoxic by activating both perforin- and FasL-pathways

“…MRL-lpr/lpr mice were bred once with C3H/HeN mice to reduce the disease severity and to keep H-2 haplotype (H-2 k ), before re-obtaining lpr/lpr mice. The TCR QM11 -Tg mouse, which bears transgenes for TCR specific for I-A k as allo-antigen, was made deficient for RAG2 gene on H-2 q background to allow CD4 + differentiation of transgenic T cells [23]. All mice used in this study were maintained in specific pathogen-free facility of Kitasato University School of Medicine.…”

Accumulation of allo-MHC cross-reactive memory T cells in bone marrow

“…Flow cytometric analyses were performed as described previously [15]. Briefly, single cell suspension of spleens or bone marrow cells were stained with FITC-, PE-, or biotin-labeled monoclonal antibody to CD4, CD8␣, CD44, CD122, TCR␤, or Sca-1 (all from BD Pharmingen, San Diego, CA) in the presence of anti-murine Fc␥RII/III antibody 2.4G2.…”

“…Five or 6 days after the second stimulation, cells were harvested and used as the effector cells in the cytolytic assay. Cell mediated cytolytic assay were performed as described previously [15]. In brief, effector cells were incubated with 5 × 10 3 /well of 51 Cr-labeled target cells for 4-8 h (as indicated) at 37 • C in 10% CO 2 .…”