ABSTRACT
A C1858T (R620W) variation in the PTPN22 gene encoding the tyrosine phosphatase LYP is a major risk factor for human autoimmunity. LYP is a known negative regulator of signaling through the T cell receptor (TCR), and murine Ptpn22 plays a role in thymic selection. However, the mechanism of action of the R620W variant in autoimmunity remains unclear. One model holds that LYP-W620 is a gain-of-function phosphatase that causes alterations in thymic negative selection and/or thymic output of regulatory T cells (Treg) through inhibition of thymic TCR signaling. To test this model, we generated mice in which the human LYP-W620 variant or its phosphatase-inactive mutant are expressed in developing thymocytes under control of the proximal Lck promoter. We found that LYP-W620 expression results in diminished thymocyte TCR signaling, thus modeling a "gain-of-function" of LYP at the signaling level. However, LYP-W620 transgenic mice display no alterations of thymic negative selection and no anomalies in thymic output of CD4(+)Foxp3(+) Treg were detected in these mice. Lck promoter-directed expression of the human transgene also causes no alteration in thymic repertoire or increase in disease severity in a model of rheumatoid arthritis, which depends on skewed thymic selection of CD4(+) T cells. Our data suggest that a gain-of-function of LYP is unlikely to increase risk of autoimmunity through alterations of thymic selection and that LYP likely acts in the periphery perhaps selectively in regulatory T cells or in another cell type to increase risk of autoimmunity.
Subject(s)
Autoimmunity , Protein Tyrosine Phosphatase, Non-Receptor Type 22/immunology , T-Lymphocytes/immunology , Thymus Gland/immunology , Animals , Arginine/genetics , CD4 Antigens/immunology , CD4 Antigens/metabolism , Female , Flow Cytometry , Forkhead Transcription Factors/immunology , Forkhead Transcription Factors/metabolism , Humans , Lymphocyte Activation/genetics , Lymphocyte Activation/immunology , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Inbred ICR , Mice, Transgenic , Mutation, Missense , Protein Tyrosine Phosphatase, Non-Receptor Type 22/genetics , Protein Tyrosine Phosphatase, Non-Receptor Type 22/metabolism , Receptors, Antigen, T-Cell/immunology , Receptors, Antigen, T-Cell/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction/genetics , Signal Transduction/immunology , T-Lymphocytes/metabolism , Thymocytes/immunology , Thymocytes/metabolism , Thymus Gland/cytology , Thymus Gland/metabolism , Tryptophan/geneticsABSTRACT
Immune cells sense microbial products through Toll-like receptors (TLR), which trigger host defense responses including type 1 interferons (IFNs) secretion. A coding polymorphism in the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene is a susceptibility allele for human autoimmune and infectious disease. We report that Ptpn22 selectively regulated type 1 IFN production after TLR engagement in myeloid cells. Ptpn22 promoted host antiviral responses and was critical for TLR agonist-induced, type 1 IFN-dependent suppression of inflammation in colitis and arthritis. PTPN22 directly associated with TNF receptor-associated factor 3 (TRAF3) and promotes TRAF3 lysine 63-linked ubiquitination. The disease-associated PTPN22W variant failed to promote TRAF3 ubiquitination, type 1 IFN upregulation, and type 1 IFN-dependent suppression of arthritis. The findings establish a candidate innate immune mechanism of action for a human autoimmunity "risk" gene in the regulation of host defense and inflammation.
