Role of the CD1a molecule in the superantigen-induced activation of MHC class II negative human thymocytes

Insulin-like growth factor I promotes cord blood T cell maturation through monocytes and inhibits their apoptosis in part through interleukin-6

Background

The functional immaturity of T cells contributes to the susceptibility of neonates to infections and the less severe graft-versus-host disease associated with cord blood (CB) transplantation. We have previously reported that insulin-like growth factor – I (IGF-I) promotes the phytohaemagglutinin (PHA)-induced CB T cell maturation and inhibits their apoptosis in mononuclear cell (MC) culture. We hypothesized that the effects of IGF-I may be mediated by accessory cells and soluble factors.

Results

This study showed that the kinetics of PHA-induced maturation in purified CD3+ T cell was delayed compared to that in CBMC. The addition of autologous CD14+ monocytes increased T cell maturation and potentiated the effect of IGF-I. The addition of IL-6 had no effect on CB T cell maturation but it reduced PHA-induced apoptosis significantly. We further demonstrated that the neutralisation of IL-6 in CBMC culture partially abrogated the anti-apoptotic effect of IGF-1 on T cells. The anti-apoptotic effect of IL-6 was not mediated via the reduction of Fas expression in T cell subsets.

Conclusion

Our results suggested that the maturation effect of IGF-1 is partially mediated by monocytes and the anti-apoptotic effect in part via IL-6. Further investigation is needed to explore the therapeutic use of IGF-I in enhancing neonatal immunity.

Regulation of CD1a surface expression and antigen presentation by invariant chain and lipid rafts

In immature dendritic cells (DCs), CD1a is almost exclusively expressed at the cell surface and its membrane organization is poorly understood. In this study, we report that MHC class II, invariant chain (Ii), and CD9 molecules are coimmunoprecipitated with CD1a in immature DCs, and that CD1a/Ii colocalization is dependent on lipid raft integrity. In HeLa-CIITA cells CD1a expression leads to increased Ii trafficking to the cell surface, confirming the relevance of this association. Furthermore, silencing of Ii in DCs induces significant CD1a accumulation on the plasma membrane whereas the total CD1a expression remains similar to that of control cells. These data suggest that CD1a recycling is facilitated by the association with the Ii. The CD1a localization in lipid rafts has functional relevance as demonstrated by inhibition of CD1a-restricted presentation following raft disruption. Overall, these findings identify Ii and lipid rafts as key regulators of CD1a organization on the surface of immature DCs and of its immunological function as Ag-presenting molecule.

Natural killer T cells are required for the development of a superantigen-driven T helper type 2 immune response in mice

We show, here, that one single injection or weekly injections of staphylococcal enterotoxin B (SEB), starting in 1-day-old newborn mice, induced a powerful immune response with a T helper type 2 (Th2) pattern, as judged by the isotype and cytokine profile, with the production of large amounts of SEB-specific immunoglobulin G1 (IgG1), detectable levels of SEB-specific IgE and increased production of interleukin-4 by spleen cells. These protocols also induced an increase in the levels of total IgE in the serum. Memory of SEB was transferred to secondary recipients by using total spleen cells from primed animals. The secondary humoral response in transferred mice was diminished if spleen cells from SEB-treated mice were previously depleted of CD3+ or Vbeta8+ T cells or NK1.1+ cells. In vivo depletion of NK1.1+ cells in adult mice resulted in a marked reduction in the SEB-specific antibody response in both the primary and secondary immune responses. Additionally, purified NK1.1+ T cells were able to perform SEB-specific helper B-cell actions in vitro and in vivo. These results suggest that NK1.1+ T cells are required for the full development of humoral immunological memory, whilst making neonatal tolerance to SEB unachievable.

Transcription factor LKLF is sufficient to program T cell quiescence via a c-Myc-dependent pathway

T lymphocytes circulate in a quiescent state until they encounter cognate antigen bound to the surface of an antigen-presenting cell. The molecular pathways that regulate T cell quiescence remain largely unknown. Here we show that forced expression of the lung Krüppel-like transcription factor (LKLF) in Jurkat T cells is sufficient to program a quiescent phenotype characterized by decreased proliferation, reduced cell size and protein synthesis and decreased surface expression of activation markers. Conversely, LKLF-deficient peripheral T cells produced by gene targeting showed increased proliferation, increased cell size and enhanced expression of surface activation markers in vivo. LKLF appeared to function, at least in part, by decreasing expression of the proto-oncogene encoding c-Myc. Forced expression of LKLF was associated with markedly decreased c-Myc expression. In addition, many effects of LKLF expression were mimicked by expression of the dominant-negative MadMyc protein and rescued by overexpression of c-Myc. Thus, LKLF is both necessary and sufficient to program quiescence in T cells and functions, in part, by negatively regulating a c-Myc--dependent pathway.