Endogenous activation of adaptive immunity: tenascin-C drives interleukin-17 synthesis in murine arthritic joint disease.

OBJECTIVE: Rheumatoid arthritis is characterized by persistent synovial inflammation and progressive joint destruction, which are mediated by innate and adaptive immune responses. Cytokine blockade successfully treats some patient subsets; however, ∼50% do not respond to this approach. Targeting of pathogenic T lymphocytes is emerging as an effective alternative/complementary therapeutic strategy, yet the factors that control T cell activation in joint disease are not well understood. Tenascin-C is an arthritogenic extracellular matrix glycoprotein that is not expressed in healthy synovium but is elevated in the rheumatoid joint, where high levels are produced by myeloid cells. Among these cells, tenascin-C expression is most highly induced in activated dendritic cells (DCs). The aim of this study was to examine the role of tenascin-C in this cell type. METHODS: We systematically compared the phenotype of DCs isolated from wild-type mice or mice with a targeted deletion of tenascin-C by assessing cell maturation, cytokine synthesis, and T cell polarization. RESULTS: Dendritic cells derived from tenascin-C-null mice exhibited no defects in maturation; induction of the class II major histocompatibility complex and the costimulatory molecules CD40 and CD86 was unimpaired. Dendritic cells that did not express tenascin-C, however, produced lower levels of inflammatory cytokines than did cells from wild-type mice and exhibited specific defects in Th17 cell polarization. Moreover, tenascin-C-null mice displayed ablated levels of interleukin-17 in the joint during experimental arthritis. CONCLUSION: These data demonstrate that tenascin-C is important in DC-mediated polarization of Th17 lymphocytes during inflammation and suggest a key role for this endogenous danger signal in driving adaptive immunity in erosive joint disease.

An Antibody Against Triggering Receptor Expressed on Myeloid Cells 1 (TREM-1) Dampens Proinflammatory Cytokine Secretion by Lamina Propria Cells from Patients with IBD.

BACKGROUND: Triggering receptor expressed on myeloid cells 1 (TREM-1) is a potent amplifier of inflammation. Recently, the antimicrobial peptide PGLYRP-1 was shown to be the ligand of TREM-1. Here, the ability of an anti-TREM-1 antibody to dampen the release of proinflammatory cytokines by colon lamina propria cells (LPCs) from patients with IBD was investigated and correlated with PGLYRP-1 levels. METHODS: Biopsies from patients with ulcerative colitis (UC, n = 45) or Crohn's disease (CD, n = 26) were compared with those from individuals undergoing colonoscopy for other reasons (n = 17). TREM-1 expression was analyzed on myeloid cells by flow cytometry. Cell culture experiments with LPCs were used to analyze PGLYRP-1 and inflammatory cytokine levels and assess the effect of anti-TREM-1 on cytokine secretion. RESULTS: The frequency of TREM-1-expressing neutrophils and recruited macrophages was higher in inflamed than in noninflamed biopsies. The PGLYRP-1 level in inflamed tissue was higher than in noninflamed tissue; it was produced primarily by neutrophils, and its level correlated with the secretion of proinflammatory cytokines. Secretion of myeloperoxidase, tumor necrosis factor-α, interleukin-1ß, and interleukin-8 by LPCs stimulated with the potent TREM-1 agonist consisting of PGLYRP-1 complexed with peptidoglycan was reduced in the presence of anti-TREM-1. Moreover, a blocking effect of anti-TREM-1 was apparent when LPCs from a subset of inflamed individuals with elevated PGLYRP-1 were stimulated with killed bacteria. CONCLUSIONS: An anti-TREM-1 antibody can dampen secretion of proinflammatory cytokines in inflamed patients with elevated PGLYRP-1. Moreover, PGLYRP-1 + myeloperoxidase is a potential biomarker for predicting the effect of anti-TREM-1 therapy.

Intrinsic T cell defects in systemic autoimmunity.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by loss of T cell tolerance to nuclear antigens. Studies in mice and humans have demonstrated that T cells from individuals with lupus are abnormal. Here, we review the known T cell defects in lupus and their possible biochemical nature, genetic causes, and significance for lupus pathogenesis.

ENU-based phenotype-driven screening.

Deciphering the contribution of individual genes and in turn pathways to cellular processes can be complicated and is often based on prior knowledge or assumptions of gene function. Phenotype-driven mutagenesis screens based around n-ethyl-n-nitrosurea (ENU) have been successful in a wide range of physiological systems in identifying novel genes that contribute to a given phenotype. Here, we describe methodologies we have employed in analysing cellular phenotypes in pipelines of mutagenised mice. Examples of primary screens to identify outliers, and secondary screens to provide a more detailed characterisation are outlined.

Detection of a secreted metalloprotease within the nuclei of liver cells.

ADAMTS13 is a secreted zinc metalloprotease expressed by various cell types. Here, we investigate its cellular pathway in endogenously expressing liver cell lines and after transient transfection with ADAMTS13. Besides compartmentalizations of the cellular secretory system, we detected an appreciable level of endogenous ADAMTS13 within the nucleus. A positively charged amino acid cluster (R-Q-R-Q-R-Q-R-R) present in the ADAMTS13 propeptide may act as a nuclear localization signal (NLS). Fusing this NLS-containing region to eGFP greatly potentiated its nuclear localization. Bioinformatics analysis suggests that the ADAMTS13 CUB-2 domain has a double-stranded beta helix (DSBH) structural architecture characteristic of various protein-protein interaction modules like nucleoplasmins, class I collagenase, tumor necrosis factor ligand superfamily, supernatant protein factor (SPF) and the B1 domain of neuropilin-2. Based on this contextual evidence and that largely conserved polar residues could be mapped on to a template CUB domain homolog, we hypothesize that a region in the ADAMTS13 CUB-2 domain with conserved polar residues might be involved in protein-protein interaction within the nucleus.

Cell signalling in macrophages, the principal innate immune effector cells of rheumatoid arthritis.

Rheumatoid arthritis is a multisystemic auto-inflammatory disease affecting up to 1% of the population and leading to the destruction of the joints. Evidence exists for the involvement of the innate as well as the adaptive immune systems in the pathology of the disease. The success of anti-tumour necrosis factor-alpha indicates the importance of pro-inflammatory mediators produced by innate immune cells in rheumatoid arthritis progression. Therefore, considerable efforts have been made in elucidating the signalling pathways leading to the expression of those mediators. This review will concentrate on the role of signalling pathways in innate immune cells in the context of rheumatoid arthritis.

The centromeric region of chromosome 7 from MRL mice (Lmb3) is an epistatic modifier of Fas for autoimmune disease expression.

Lupus is a prototypic systemic autoimmune disease that has a significant genetic component in its etiology. Several genome-wide screens have identified multiple loci that contribute to disease susceptibility in lupus-prone mice, including the Fas-deficient MRL/Fas(lpr) strain, with each locus contributing in a threshold liability manner. The centromeric region of chromosome 7 was identified as a lupus susceptibility locus in MRL/Fas(lpr) mice as Lmb3. This locus was backcrossed onto the resistant C57BL/6 (B6) background, in the presence or absence of Fas, resulting in the generation of B6.MRLc7 congenic animals. Detailed analysis of these animals showed that Lmb3 enhances and accelerates several characteristics of lupus, including autoantibody production, kidney disease, and T cell activation, as well as accumulation of CD4(-)CD8(-) double-negative T cells, the latter a feature of Fas-deficient mice. These effects appeared to be dependent on the interaction between Lmb3 and Fas deficiency, as Lmb3 on the B6/+(Fas-lpr) background did not augment any of the lupus traits measured. These findings confirm the role of Lmb3 in lupus susceptibility, as a modifier of Fas(lpr) phenotype, and illustrate the importance of epistatic interaction between genetic loci in the etiology of lupus. Furthermore, they suggest that the genetic lesion(s) in MRLc7 is probably different from those in NZMc7 (Sle3/5), despite a significant overlap of these two intervals.

Oxazolone and diclofenac-induced popliteal lymph node assay reactions are attenuated in mice orally pretreated with the respective compound: potential role for the induction of regulatory mechanisms following enteric administration.

The murine popliteal lymph node assay (PLNA) was examined as a preclinical assay with the potential to identify low-molecular-weight compounds (LMWCs) that are likely to be associated with immune-mediated drug hypersensitivity reactions (IDHRs) in humans. We hypothesized that the contact sensitizer oxazolone (OX) would cause a strong PLN reaction in naive mice and that the PLN reaction would be attenuated in mice orally pretreated with OX due to the induction of oral tolerance. In naive mice, OX induced a strong PLN reaction and caused dose-dependent increases in PLN size, weight, cellularity, percentage of CD4(+) PLN T cells, and percentage of PLN B cells, with a concomitant decrease in the percentage of CD8(+) PLN T cells. Next, the PLNA was conducted in mice gavaged three times with either OX or vehicle alone (olive oil). Mice pretreated with OX had suppressed PLN reactions following the footpad injection of OX (decrease in PLN size, weight, and cellularity), which was associated with an increase in the percentage of PLN CD8(+)T cells. In contrast, oral pretreatment with OX had no observable effect on the PLN reaction induced following footpad injection of the irrelevant hapten dinitrochlorobenzene (DNCB). Adoptive transfer studies were conducted to examine the mechanism of PLN hyporesponsiveness. It was found that either (1) unfractionated splenocytes or (2) purified CD8(+) splenocytes, but not (3) purified CD4(+) splenocytes isolated from mice gavaged with OX adoptively transferred PLN suppression to naive BALB/c mice. Because OX is not a pharmaceutical, we also examined the NSAID diclofenac (DF) (Voltaren). Like OX, DF caused dose-dependent increases in PLN size, weight, and cellularity in naive mice. Furthermore, like OX, the diclofenac-induced PLN reaction was attenuated in mice that had been orally pretreated three times with DF. However, splenocytes from mice orally treated with DF were not able to adoptively transfer PLN hyporesponsiveness. Collectively, these observations demonstrate that both OX and DF are potent immunostimulators in the PLNA. As importantly, these results demonstrate that the immunostimulating potential of OX and DF in the PLNA is significantly decreased in mice orally exposed to the respective drug, possibly due to the presence of a cellular mechanism of oral tolerance. For OX, the mechanism appears to involve, in part, CD8(+) T cells, whereas the mechanism(s) associated with PLN hyporesponsiveness using DF remain to be defined.