Mechanisms of asthma and allergic inflammation
Superantigen-induced corticosteroid resistance of human T cells occurs through activation of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK-ERK) pathway

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Background

Microbial superantigens induce human T-cell resistance to corticosteroids.

Objective

Understanding the molecular pathways resulting in corticosteroid-resistant T cells is important because this condition can complicate the treatment of inflammation.

Methods

The response of human PBMCs to steroids was assessed by using proliferation assays after stimulation with superantigens or anti-CD3 in the presence of various kinase inhibitors. Glucocorticoid receptor α (GCRα) localization was defined on the basis of intracellular staining. Protein phosphorylation was measured by means of Western blotting.

Results

In the current study we found that PBMCs stimulated with superantigen, but not anti-CD3, induced corticosteroid-resistant T cells. However, the purified T cells stimulated either with staphylococcal enterotoxin B (SEB) or anti-CD3 are susceptible to corticosteroid inhibition. These results imply that signals on antigen-presenting cells might act in concert with the T-cell receptor to cause steroid resistance. Blockade of CD40–CD40 ligand interaction had no effect on superantigen-induced corticosteroid resistance. However, CD28 costimulation with T-cell receptor activation induced corticosteroid resistance of human T cells in a dose-dependent manner. Superantigen stimulation, compared with anti-CD3 stimulation, was found to induce a more rapid and sustained phosphorylation of mitogen-activated extracellular signal-regulated kinase (ERK). Treatment with PD98059 and UO126 (specific mitogen-activated protein kinase kinase [MEK]/ERK inhibitors), but not a p38 inhibitor or a c-Jun N-terminal kinase inhibitor, restored the response to steroids, as indicated by proliferation assays. Furthermore, purified ERK1 and ERK2 were able to phosphorylate recombinant human GCRα directly in an in vitro kinase assay. Of note, superantigen-induced corticosteroid resistance was associated with abrogation of GCRα nuclear translocation. This effect could be reversed by treatment with MEK/ERK pathway inhibitors.

Conclusions

These data are compatible with the hypothesis that superantigen-induced corticosteroid resistance involves the Raf-MEK-ERK1/ERK2 pathway of T-cell receptor signaling, which leads to GCRα phosphorylation and inhibition of dexamethasone-induced GCRα nuclear translocation.

Section snippets

Reagents

Staphylococcal enterotoxin B (SEB), toxic shock syndrome toxin 1 (TSST-1; Toxin Technology, Sarasota, Fla), anti-human CD3 (Orthoclone OKT 3 sterile solution; Ortho Biotech Products, L.P., Raritan, NJ), CD28 (BD PharMingen, San Diego, Calif), and dexamethasone (Sigma Chemicals Co, St Louis, Mo) were used for cell stimulation. The p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 (inhibitory concentration of 50% [IC50] = 35 nM), the MEK inhibitors U0126 (IC50 = 72 nM) and PD98059 (IC50 = 

Cellular requirements for superantigen-induced CR T cells

Because superantigens are known to activate T cells through the TCR, our initial experiments compared the effects of dexamethasone on superantigen (SEB or TSST-1) versus anti-CD3-induced proliferation of human T cells. As shown in Fig 1, A, dexamethasone significantly inhibited the T-cell proliferation induced by anti-CD3. In contrast, SEB-induced (Fig 1, A) or TSST-induced (data not shown) T-cell proliferation was not affected by dexamethasone. This difference in steroid responsiveness between

Discussion

The anti-inflammatory and immunosuppressive properties of corticosteroids are their major pharmacologic benefits and make them the most widely prescribed class of drugs in the world. The physiologic response and sensitivity to corticosteroids varies among individuals, tissues, and cell types.7 As such, corticosteroid resistance complicates the treatment of chronic inflammatory diseases. Although not proved, we hypothesize that superantigens contribute to the severity of various diseases by

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    Dr Leung's work was supported in part by National Institutes of Health grants HL36577, AR41256, and HL37260; the Ann and Louis Rudolph Kawasaki Disease Research Fund; and the Edelstein Family Chair in Pediatric Allergy and Immunology, the University of Colorado Cancer Center.

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    Copyright © 2004 American Academy of Allergy, Asthma and Immunology. Published by Mosby, Inc. All rights reserved.