IL-10 inhibits CD28 and ICOS costimulations of T cells via src homology 2 domain—containing protein tyrosine phosphatase 1

Background

Specific T-cell activation requires T-cell receptor stimulation and the generation of costimulatory signals. Major costimulatory signals are delivered to T cells by the interaction of CD28 and inducible costimulator (ICOS).

Objective

To investigate the molecular pathways involved in direct T-cell suppression by IL-10.

Methods

T-cell proliferation analysis, immunoprecipitations, and Western blots were performed after T-cell receptor and CD28 and ICOS stimulations in the absence or presence of IL-10. Dominant-negative src homology 2 domain–containing protein tyrosine phosphatase 1 (SHP-1) overexpression, small inhibitory RNA, and SHP-1–deficient and IL-10–deficient mice were used.

Results

IL-10 receptor–associated tyrosine kinase Tyk-2 acts as a constitutive reservoir for SHP-1 in resting T cells, and then tyrosine phosphorylates SHP-1 on IL-10 binding. SHP-1 rapidly binds to CD28 and ICOS costimulatory receptors and dephosphorylates them within minutes. In consequence, the binding of phosphatidylinositol 3-kinase to either costimulatory receptor no longer occurs, and downstream signaling is inhibited. Accordingly, spleen cells from SHP-1–deficient mice showed increased proliferation with CD28 and ICOS stimulation in comparison with wild-type mice, which was not suppressed by IL-10. Generation of dominant-negative SHP-1–overexpressing T cells or silencing of the SHP-1 gene by small inhibitory RNA both altered SHP-1 functions and abolished the T-cell suppressive effect of IL-10.

Conclusion

The rapid inhibition of the CD28 or ICOS costimulatory pathways by SHP-1 represents a novel mechanism for direct T-cell suppression by IL-10.

Clinical implications

Molecular mechanisms of direct T-cell suppression by IL-10 may provide a novel target for therapy of allergy/asthma and autoimmune disease.

Key words: IL-10, T cell, suppression, costimulation, anergy, SHP-1, phosphorylation, tolerance, inhibition

Abbreviations used: CFSE, Carboxyfluorescein succinimidyl ester, cRPMI, Complete Roswell Park Memorial Institute, DN, Dominant-negative, GALV, Gibbon ape leukemia virus, GFP, Green fluorescent protein, HA, Hemagglutinin, ICOS, Inducible costimulator, ITAM, Immunoreceptor tyrosine-based activation motif, ITIM, Immunoreceptor tyrosine-based inhibition motif, MLV, Moloney murine leukemia virus, NGFR, Nerve growth factor receptor, PI3-K, Phosphatidylinositol 3-kinase, PPD, Purified protein derivative, SEB, Staphylococcal enterotoxin B, SH2, Src-homology-2, SHP-1, Src homology 2 domain–containing protein tyrosine phosphatase 1, siRNA, Small inhibitory RNA, STAT, Signal transducer and activator of transcription, TCR, T-cell receptor