Molecular basis for T cell response induced by altered peptide ligand of type II collagen

The role of Syk in peripheral T cells

The aim of this study was to understand how Syk affects peripheral T cell function. T cells from Syk^-/- chimeric mice and DR1 Syk^fl/fl CD4^cre conditional mice gave strong CD3-induced Th1, Th2, and Th17 cytokine responses. However, an altered peptide ligand (APL) of human CII (256-276) with two substitutions (F263N, E266D), also called A12, elicited only Th2 cytokine responses from Syk^fl/fl T cells but not Syk^fl/fl-CD4^cre T cells. Western blots revealed a marked increase in the phosphorylation of Syk, JNK and p38 upon A12/DR1 activation in WT or Syk^fl/fl T cells but not in Syk^fl/flCD4^-cre cells. We demonstrate that Syk is required for the APL- induction of suppressive cytokines. Chemical Syk inhibitors blocked activation of GATA-3 by peptide A12/DR1. In conclusion, this study provides novel insights into the role that Syk plays in directing T cell activity, and may shape therapeutic approaches for autoimmune diseases.

The Role of Leukocyte-Associated Ig-like Receptor-1 in Suppressing Collagen-Induced Arthritis

Several observations implicate a critical role for T cell dysregulation as a central problem in rheumatoid arthritis. We investigated a mechanism for suppressing T cell activation by stimulating a natural inhibitory receptor called leukocyte-associated Ig-like receptor-1 (LAIR-1). The collagen-induced arthritis (CIA) model and DR-1 transgenic mice were used to study the importance of LAIR-1 in autoimmune arthritis. Splenocytes from wild-type or LAIR-1^-/- mice were stimulated with soluble anti-CD3 Ab in the presence or absence of α1(II) and supernatants were collected for cytokine analysis. B6.DR1 mice were immunized with type II collagen/CFA to induce arthritis and were treated with either the stimulatory mAb to LAIR-1 or a hamster IgG control. Finally, B6.DR1/LAIR-1^-/- and B6.DR1/LAIR-1^+/+ mice were challenged for CIA and mean severity scores were recorded thrice weekly. Using splenocytes or purified CD4⁺ cells that were sufficient in LAIR-1, CD3-induced cytokine secretion was significantly suppressed in the presence of collagen, whereas LAIR-1-deficient splenocytes had no attenuation. Treatment with a stimulatory mAb to LAIR-1 also significantly attenuated CIA in the LAIR^+/+ mice. When B6.DR1/LAIR-1^-/- mice were immunized with type II collagen they developed more severe arthritis and had a greater percentage of affected limbs than the wild-type mice. These data demonstrate that collagen can suppress the T cell cytokine response through the action of LAIR-1. Treatment with stimulating LAIR-1 Abs suppresses CIA whereas B6.DR1/LAIR-1^-/- mice develop more severe arthritis than wild-type controls. These data suggest that LAIR-1 may be a potential therapeutic target for suppressing rheumatoid arthritis.

Characterization of the Syk-Dependent T Cell Signaling Response to an Altered Peptide

Rheumatoid arthritis is an autoimmune disorder characterized by T cell dysregulation. We have shown that an altered peptide ligand (A9) activates T cells to use an alternate signaling pathway that is dependent on FcRγ and spleen tyrosine kinase, resulting in downregulation of inflammation. In the experiments described in this study, we have attempted to determine the molecular basis of this paradox. Three major Src family kinases found in T cells (Lck, Fyn, and Lyn) were tested for activation following stimulation by A9/I-A^q Unexpectedly we found they are not required for T cell functions induced by A9/I-A^q, nor are they required for APL stimulation of cytokines. On the other hand, the induction of the second messenger inositol trisphosphate and the mobilization of calcium are clearly triggered by the APL A9/I-A^q stimulation and are required for cytokine production, albeit the cytokines induced are different from those produced after activation of the canonical pathway. DBA/1 mice doubly deficient in IL-4 and IL-10 were used to confirm that these two cytokines are important for the APL-induced attenuation of arthritis. These studies provide a basis for exploring the effectiveness of analog peptides and the inhibitory T cells they induce as therapeutic tools for autoimmune arthritis.

The anergy induction of M3 muscarinic acetylcholine receptor-reactive CD4+ T cells suppresses experimental sialadenitis-like Sjögren's syndrome

OBJECTIVE

Autoreactive CD4+ T cells are involved in the pathogenesis of Sjögren's syndrome (SS). The aim of the present study was to clarify the dominant T cell epitopes of M3 muscarinic acetylcholine receptor (M3R) and to establish a new antigen-specific therapy for SS using an experimental mouse model.

METHODS

Production of cytokines from M3R-reactive CD4+ T cells, after culture with various M3R peptides, was analyzed by enzyme-linked immunosorbent assay. Adoptive cell transfer was performed using splenocytes from M3R(-/-) mice that were immunized with M3R peptides or phosphate buffered saline plus H37Ra as a control. Rag1(-/-) mice were inoculated with the splenocytes and examined for the development of sialadenitis. Altered peptide ligands (APLs) of the T cell epitopes, with substitutions in amino acid residues at T cell receptor contact sites, were synthesized, and the ability of the APLs to suppress sialadenitis was evaluated. The mechanisms underlying such effects were assessed.

RESULTS

CD4+ M3R-reactive T cells produced interleukin-17 (IL-17) and interferon-γ (IFNγ) in response to the N-terminal 1 (N1) and 1st extracellular loop peptides of M3R, and Rag1(-/-) mice that received N1- and/or 1st peptide-immunized splenocytes developed sialadenitis. Among the designed APLs, N1-APL7 (N→S at amino acid 15) significantly suppressed IFNγ production in vitro, and also suppressed sialadenitis in vivo. Levels of early growth response 2 in CD4+ T cells from the cervical lymph nodes of N1-APL7-treated mice were significantly higher than those of control mice, and cell proliferation was reversed by administration of exogenous IL-2. Levels of the anergy-related molecules itchy homolog E3 ubiquitin-protein ligase, Casitas B-lineage lymphoma b, gene related to anergy in lymphocytes, and Deltex-1 were significantly higher in CD4+ T cells cultured with N1-APL7.

CONCLUSION

The major T cell epitopes were from the N1 and 1st peptide regions. Moreover, N1-APL7, selected as the antagonistic APL in vitro, also suppressed sialadenitis through the induction of anergy. This is a potentially useful strategy for regulating pathogenic T cell infiltration in SS.

Peptide ligand structure and I-Aq binding avidity influence T cell signaling pathway utilization

Factors that drive T cells to signal through differing pathways remain unclear. We have shown that an altered peptide ligand (A9) activates T cells to utilize an alternate signaling pathway which is dependent upon FcRγ and Syk. However, it remains unknown whether the affinity of peptide binding to MHC drives this selection. To answer this question we developed a panel of peptides designed so that amino acids interacting with the p6 and p9 predicted MHC binding pockets were altered. Analogs were tested for binding to I-A(q) using a competitive binding assay and selected analogs were administered to arthritic mice. Using the collagen-induced arthritis (CIA) model, arthritis severity was correlated with T cell cytokine production and molecular T cell signaling responses. We establish that reduced affinity of interaction with the MHC correlates with T cell signaling through the alternative pathway, leading ultimately to secretion of suppressive cytokines and attenuation of arthritis.