Summary Systemic Lupus Erythematosus (SLE) is characterized by B-cells lacking IgD and CD27 (double negative; DN). We show that DN cell expansions reflected a subset of CXCR5−CD11c+ cells (DN2) representing pre-plasma cells (PC). DN2 cells predominated in African-American patients with active disease and nephritis, anti-Smith and anti-RNA autoantibodies. They expressed a T-bet transcriptional network; increased toll-like receptor-7 (TLR7); lacked the negative TLR regulator TRAF5; and were hyper-responsive to TLR7. DN2 cells shared with activated naïve cells (aNAV), phenotypic and functional features, and similar transcriptomes. Their PC differentiation and autoantibody production was driven by TLR7 in an interleukin-21 (IL-21)-mediated fashion. An in vivo developmental link between aNAV, DN2 cells and PC was demonstrated by clonal sharing. This study defines a distinct differentiation fate of autoreactive naïve B cells into PC precursors with hyper-responsiveness to innate stimuli, as well as establishes prominence of extra-follicular B-cell activation in SLE, and identifies therapeutic targets.

Iimmune regulatory proteins such as CIITA, NAIP, IPAF, NOD1, NOD2, NALP1, cryopyrin/ NALP3 are members of a family characterized by the presence of a nucleotide-binding domain (NBD) and leucine-rich repeats (LRR). Members of this gene family encode a protein structure similar to the NB-LRR subgroup of disease-resistance genes in plants and are involved in the sensing of pathogenic products and the regulation of cell signaling and apoptosis. Several members of this family have been associated with immunologic disorders. NOD2 for instance is associated with both Crohn's disease and Blau syndrome.

A complementary DNA (cDNA) for ubiquitin carboxyl-terminal hydrolase isozyme L3 was cloned from human B cells. The cDNA encodes a protein of 230 amino acids with a molecular mass of 26.182 daltons. The human protein is very similar to the bovine homolog, with only three amino acids differing in over 100 residues compared. The amino acid sequence deduced from the cDNA was 54% identical to that of the neuron-specific protein PGP 9.5. Purification of bovine PGP 9.5 confirmed that it is also a ubiquitin carboxyl-terminal hydrolase. These results suggest that a family of such related proteins exists and that their expression is tissue-specific.

T cell exhaustion plays a major role in failure to control chronic infections. High expression of inhibitory receptors, including PD-1, and the inability to sustain functional T cell responses contribute to exhaustion. However, the transcriptional control of these processes remains unclear. Here we demonstrate that the transcription factor T-bet regulates CD8+ T cell exhaustion and inhibitory receptor expression. T-bet directly repressed Pdcd1 transcription and decreased the expression of other inhibitory receptors. While elevated T-bet promoted terminal differentiation following acute infection, high T-bet expression sustained exhausted CD8+ T cells and repressed inhibitory receptor expression during chronic viral infection. Persisting antigenic stimulation caused T-bet downregulation, which resulted in more severe exhaustion of CD8+ T cells. These observations suggest therapeutic opportunities involving increasing T-bet expression during chronic infection.

SUMMARY Functionally exhausted T cells express high levels of the PD-1 inhibitory receptor, and therapies that block PD-1 signaling show promise for resolving chronic viral infections and cancer. Using human and murine systems of acute and chronic viral infections we analyzed epigenetic regulation of PD-1 expression during CD8 T cell differentiation. During acute infection, naïve to effector CD8 T cell differentiation was accompanied by a transient loss of DNA methylation of the Pdcd1 locus that was directly coupled to the duration and strength of TCR signaling. Further differentiation into functional memory cells coincided with Pdcd1 remethylation providing an adapted program for regulation of PD-1 expression. In contrast, the Pdcd1 regulatory region was completely demethylated in exhausted CD8 T cells and remained unmethylated even when virus titers decreased. This lack of DNA remethylation leaves the Pdcd1 locus poised for rapid expression, potentially providing a signal for premature termination of antiviral functions.

No abstract

P rogrammed death-1 (CD279) is a transmembrane protein that shares homology with the B7/CD28 family of T cell signaling molecules (1). PD-1 interactions with its ligands PD-L1 and/or PD-L2 provides a negative regulatory signal to CD4 and CD8 T cells that results ultimately in a phenotype termed T cell exhaustion (2, 3). Exhausted T cells have lost the ability to combat invading pathogens, synthesize cytokines, and proliferate (4 -6). Specific examples include T cell responses toward chronic viral infections caused by HIV and lymphocytic choriomeningitis virus (LCMV) (7-11). Molecular blockade of the interaction between PD-1 and its ligands results in the reinvigoration of the exhausted T cell's effector functions, enabling cytotoxic action and cytokine release, suggesting that the PD-1 pathway is reversible (11,12).Depending on the model used, genetic studies showed that deletion of the PD-1 gene ( pdcd1) in mice resulted in the manifestation of spontaneous autoimmune diseases, including arthritis, gastritis, and cardiomyopathy (13-15). Other studies have concluded that the PD-1/PD-L1 pathway also plays a role in the onset of diabetes and encephalomyelitis in mice (16,17). In humans, polymorphisms within pdcd1 have been linked to multiple sclerosis, rheumatoid arthritis, type 1 diabetes, and systemic lupus erythematosus (18 -21). Additionally, aberrant PD-1 function and/or misregulation have been implicated in aiding tumor evasion from the immune system and playing a role in graft-vs-host disease (18 -26). These studies suggest that PD-1 is likely to be critically involved in the development and maintenance of peripheral tolerance. PD-1 expression is restricted to cells of the immune system.Early studies demonstrated that PD-1 was up-regulated in thymocyte populations exposed to apoptotic stimuli (27). PD-1 is expressed on thymocytes at the early double negative and double positive stages; however, the full significance of PD-1 expression at these stages is not known. In addition to appearing on the surfaces of exhausted T cells, PD-1 is transiently expressed following T cell activation.Upon T cell activation, family members of the NFAT are dephosphorylated and translocate to the nucleus where they can activate target genes (28). Nuclear translocation of NFAT is abrogated by inhibition of the phosphatase activity of calcineurin with immunophilin-interacting compounds such as cyclosporine A (29 -31). Examination of cDNA microarray data comparing exhausted, effector, and memory CD8 T cells showed an increase in NFATc1 (also called NFAT2) expression, suggesting a possibility for its role in regulating PD-1 transcription (32).Despite PD-1's role in immune responses and its association with disease, little is known about the regulation of this critical gene. In this study, an unbiased approach was taken to determine the mechanism of PD-1 regulation during T cell activation as a first step in understanding the regulatory pathway that controls this gene during complex immune responses. The results have identified two 5...

The transcriptional repressor BCL-6 regulates B lymphocyte cell fate during the germinal center reaction by preventing terminal differentiation of B lymphocytes into plasma cells until appropriate signals are received. Here, we report a cofactor, MTA3, a cell type-specific subunit of the corepressor complex Mi-2/NuRD, for BCL-6-dependent cell fate determination. MTA3 is expressed in the same pattern in germinal centers as BCL-6. BCL-6 physically interacts with Mi-2/NuRD and this interaction is sensitive to BCL-6 acetylation status. Depletion of MTA3 by RNAi impairs BCL-6-dependent repression and alters the cell-specific transcriptional pattern characteristic of the B lymphocyte. Remarkably, exogenous expression of BCL-6 in a plasma cell line leads, in an MTA3-dependent manner, to repression of plasma cell-specific transcripts, reactivation of the B cell transcriptional program, expression of B lymphocyte cell surface markers, and reprogramming of cell fate.