ABSTRACT
Plasmacytoid dendritic cells (PDCs), which produce IFN-alpha in response to autoimmune complexes containing nuclear antigens, are thought to be critically involved in the pathogenesis of systemic lupus erythematosus (SLE). One of the immunostimulatory components of SLE immune complexes (SLE-ICs) is self DNA, which is recognized through Tlr9 in PDCs and B cells. Small nuclear ribonucleoproteins (snRNPs) are another major component of SLE-ICs in 30% to 40% of patients. In this study, we show that murine PDCs are activated by purified U1snRNP/anti-Sm ICs to produce IFN-alpha and proinflammatory cytokines and to up-regulate costimulatory molecules. The induction of IFN-alpha and IL-6 by U1snRNPs in murine bone marrow-derived PDCs required the presence of intact U1RNA and was largely dependent on Tlr7 but independent of Tlr3. Intracellularly delivered isolated U1snRNA and oligoribonucleotides derived from the stem loop regions and the Sm-binding site of U1snRNA efficiently induced IFN-alpha and IL-6 in Flt3L-cultured DCs in a Tlr7-dependent manner. The U1snRNA component of U1snRNP immune complexes, found in patients with SLE, acts as an endogenous "self" ligand for Tlr7 and triggers IFN-alpha and IL-6 production in PDCs.
Subject(s)
Antibodies, Antinuclear/immunology , Antigen-Antibody Complex/immunology , Dendritic Cells/immunology , Interferon-alpha/immunology , Membrane Glycoproteins/immunology , Plasma Cells/immunology , Ribonucleoprotein, U1 Small Nuclear/immunology , Toll-Like Receptor 7/immunology , Animals , Antibodies, Antinuclear/pharmacology , Antigen-Antibody Complex/pharmacology , Cells, Cultured , Dendritic Cells/metabolism , Dendritic Cells/pathology , Humans , Interferon-alpha/biosynthesis , Interleukin-6/biosynthesis , Interleukin-6/immunology , Lupus Erythematosus, Systemic/immunology , Lupus Erythematosus, Systemic/metabolism , Lupus Erythematosus, Systemic/pathology , Membrane Glycoproteins/deficiency , Mice , Mice, Knockout , Oligoribonucleotides/immunology , Oligoribonucleotides/pharmacology , Plasma Cells/metabolism , Plasma Cells/pathology , Ribonucleoprotein, U1 Small Nuclear/pharmacology , Toll-Like Receptor 7/deficiency , fms-Like Tyrosine Kinase 3/immunologyABSTRACT
A peptide encompassing residues 131-151 of the spliceosomal U1-70K protein and its analog phosphorylated at Ser140 were synthesized as potential candidates for the treatment of patients with lupus. Studies in the MRL/lpr and (NZB x NZW)F1 lupus models have demonstrated that these sequences contain a CD4+ T cell epitope but administration of the phosphorylated peptide only ameliorates the clinical manifestations of treated MRL/lpr mice. Binding assays with soluble HLA class II molecules and molecular modeling experiments indicate that both peptides behave as promiscuous epitopes and bind to a large panel of human DR molecules. In contrast to normal T cells and T cells from non-lupus autoimmune patients, we found that PBMCs from 40% of lupus patients selected randomly and CFSE-labeled CD4+ T cells proliferate in response to peptide 131-151. Remarkably, however, we observed that phosphorylation of Ser140 prevents CD4+ T cells proliferation but not secretion of regulatory cytokines, suggesting a striking immunomodulatory effect of phosphorylated analog on lupus CD4+ T cells that was unique to patients. The analog might act as an activator of regulatory T cells or as a partial agonist of TCR.
