Mitogen-activated kinase kinase kinase 1 regulates T cell receptor- and CD28-mediated signaling events which lead to NF-kappaB activation

Optimal activation of Rel/NF-kappaB transcription factors in T lymphocytes requires a CD28-delivered co-stimulatory signal in addition to TCR engagement. Although, Rel/NF-kappaB transcription factors are critical regulators of many T cell functions, the mechanisms and molecules, which link the surface receptors to their activation, are poorly characterized. Using Jurkat T cells stimulated with superantigen presented on B7-positive APC, we showed that CD28- and TCR-stimulated NF-kappaB-dependent transcription is associated to the activation of IkappaB kinase beta (IKKbeta) and, to a lesser extent, of IkappaB kinase alpha (IKKalpha). A dominant negative mutant of the MAP3 kinase MEKK1, a kinase known to regulate the JNK pathway and to activate NF-kappaB-dependent transcription in many cell types, strongly inhibits CD28- and TCR-induced IKK activity, whereas the dominant negative mutants of the NF-kappaB-inducing kinase (NIK) did not exert any significant effects. In addition, TCR/CD28 stimulation results in the recruitment and autophosphorylation of endogenous MEKK1, whereas endogenous NIK was not detectably activated. Our data identify MEKK1 as a critical step in coupling signals initiated by TCR and CD28 to the downstream pathways which lead to both AP-1 and NF-kappaB activation in T lymphocytes.

Peptide analogues as a strategy to induce tolerance in T cells with indirect allospecificity

BACKGROUND

It has been demonstrated that indirect recognition of allogeneic MHC molecules might play an important role in provoking graft rejection. Although direct recognition of allogeneic molecules on antigen presenting cells of the graft may induce a state of tolerance, the continuous presentation of processed alloantigens by specialized antigen presenting cells does not allow the same phenomenon to occur. Tolerance to interleukin-2 secreting T cells can be achieved in different ways, among these is the exposure to mutants of the wild type allopeptide. We have investigated whether peptide analogues of the allopeptide can induce tolerance in T cells with indirect allospecificity.

METHODS

T cell clones with indirect anti-HLA-A2-specificity generated from a HLA-A2-DRB1*1502+ patient who chronically rejected a HLA-A2-expressing kidney allograft were used for this study. Nine peptide analogues of HLA-A2 (residues: 103-120) were produced with single amino acid substitutions at the putative T cell receptor for antigen contact positions. Their effect on the proliferation of a panel of T cell clones was evaluated.

RESULTS

Peptide analogues and wild type peptide had similar capacity to bind to the restriction molecule HLA-DRB1*1502. Co-presentation of the peptide analogues 111R/A, H, K and 114H/K, with the wild type peptide inhibited T cell responses, indicative of antagonism. In addition, one analogue 112G/S induced unresponsiveness in the T cells to subsequent culture with the wild type peptide.

CONCLUSIONS

The data presented here suggest that using reagents such as altered peptides may represent a strategy to prevent the activation of T cells with indirect alloreactivity and allograft rejection in vivo.

Flipping assumptions and revisioning perioperative services

As we approach a fully capitated healthcare environment, total revisioning and restructuring of hospitals as a whole, and perioperative services in particular, will be necessary to maintain the financial viability of our healthcare institutions. Nurse executives will be in pivotal roles in leading and influencing these hospital initiatives. The authors present a vision of the new hospital and discuss methods of responding to change within the healthcare environment, with an emphasis on perioperative services. An analysis of the findings of an operating room survey conducted with nurse executives is included in the discussion.

Hypervariable region 1 variants act as TCR antagonists for hepatitis C virus-specific CD4+ T cells

In various human viral infections, the appearance of mutated epitopes displaying TCR antagonistic activity has been correlated with the severity and persistence of infection. In hepatitis C virus (HCV) infection, where the virus persistence has been associated with the rapid and substantial Ag modifications occurring during replication, TCR antagonism has been evidenced in CD8+ T cell responses. However, CD4+ T cell antagonism may be another important strategy by which HCV eludes a protective response, because sustained Th responses directed against several HCV Ags are associated with a self-limited course of infection. The data reported here represent the first evidence that variants of the hypervariable region (HVR1) of the putative Envelope 2 protein of HCV can act as powerful TCR antagonists for HVR1-specific CD4+ T cells isolated from HCV-infected individuals. Using classical antagonism assays, we observed strong inhibition of cellular proliferation and cytokine production when the agonist and the antagonist ligands were simultaneously presented by the same APCs. The presence in HVR1 of conserved residues, critical for binding to HLA-DR molecules, supports the function of HVR1 variants as TCR antagonists. In conclusion, our data evidence an antagonism phenomenon, which was achieved by naturally occurring class II-restricted T cell epitopes whose mechanism was addressed in terms of the antagonist capacity to inhibit agonist-mediated TCR down-regulation and early signal transduction.