We studied ten individuals from eight families showing features consistent with the immuno-osseus dysplasia spondyloenchondrodysplasia (SPENCD). Of particular note was the diverse spectrum of autoimmune phenotypes observed in these patients, including systemic lupus erythematosus (SLE), Sjögren's syndrome, haemolytic anemia, thrombocytopenia, hypothyroidism, inflammatory myositis, Raynaud's disease, and vitiligo. Haplotype data indicated the disease gene to be on chromosome 19p13 and linkage analysis yielded a combined multipoint lod score of 3.6. Sequencing of the ACP5 gene, encoding tartrate resistant acid phosphatase (TRAP), identified biallelic mutations in each of the patients studied, and in vivo testing confirmed a loss of expressed protein. All eight patients assayed demonstrated elevated serum interferon alpha activity, and gene expression profiling in whole blood defined a type I interferon signature. Our findings reveal a previously unrecognised link between TRAP activity and interferon metabolism, and highlight the importance of type I interferon in the genesis of autoimmunity.

Transgenic expression of TLR7 results in the expansion and hyperactivation of T1 B cells in response to endogenous RNA complexes, leading to increased autoantibody production.

Significant progress has been made in defining both TLR as well as non-TLR mediated stimulation of IFN-I. This has helped elucidate the mechanisms of several mutations and common genetic variations in predisposing to SLE. Challenges remain in the establishing the utility of biomarkers and the role of IFN-I blockade in the clinical management of patients with this disease.

No abstract

Monocytes in patients with systemic lupus erythematosus (SLE) are hyperstimulatory for T lymphocytes. We previously found that the normal program for expression of a negative costimulatory molecule programmed death ligand-1 (PD-L1) is defective in SLE patients with active disease. Here, we investigated the mechanism for PD-L1 dysregulation on lupus monocytes. We found that PD-L1 expression on cultured SLE monocytes correlated with TNF-α expression. Exogenous TNF-α restored PD-L1 expression on lupus monocytes. Conversely, TGF-β inversely correlated with PD-L1 in SLE and suppressed expression of PD-L1 on healthy monocytes. Therefore, PD-L1 expression in monocytes is regulated by opposing actions of TNF-α and TGF-β. As PD-L1 functions to fine tune lymphocyte activation, dysregulation of cytokines resulting in reduced expression could lead to loss of peripheral T cell tolerance.

These data are the first to link active lupus with reversibly decreased PD-L1 expression on professional APC, suggesting a novel mechanism for loss of peripheral tolerance in SLE.

Immune complexes (ICs) play a pivotal role in causing inflammation in systemic lupus erythematosus (SLE)3. Yet, it remains unclear what the dominant blood cell type(s) and inflammation related gene programs stimulated by lupus ICs are. To address these questions, we exposed normal human peripheral blood mononuclear cells (PBMCs) or CD14+ isolated monocytes to SLE ICs in the presence or absence of C1q and performed microarray analysis and other tests for cell activation. By microarray analysis, we identified genes and pathways regulated by SLE ICs that are both type I IFN dependent and independent. We also found that C1q containing ICs markedly reduced expression of the majority of IFN-response genes and also influenced the expression of multiple other genes induced by SLE ICs. Surprisingly, IC activation of isolated CD14+ monocytes did not upregulate CD40 and CD86 and only modestly stimulated inflammatory gene expression. However, when monocyte subsets were purified and analyzed separately, the low abundance CD14dim (‘patrolling’) subpopulation was more responsive to ICs. These observations demonstrate the importance of plasmacytoid dendritic cells (pDCs), CD14dim monocytes and C1q as key regulators of inflammatory properties of ICs and identify many pathways through which they act.

IgG attenuates IFNα production by PDCs by both cell surface receptor and intracellular pathways, depending on the nature of the inducing stimulus.