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ARE Missing in SLE TCR 
mRNA
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mRNA missing nt 672-1233 within its 3'-untranslated region (UTR) in T cells of patients with systemic lupus erythematosus (SLE). Although 3'-UTRs are implicated in posttranscriptional control of eukaryotic mRNAs, their mechanism of action is unknown. Chowdhury et al. (p. 8248
) from the Tsokos laboratory, found decreased TCR protein expression in monkey cells transfected with a vector containing TCR mRNA carrying the AS 3'-UTR compared with the splice-deleted (SD) sequence (nt 672-1233) or wild-type 3'-UTR. TCR mRNA stability and protein expression were reduced more in cells transfected with the AS 3'-UTR construct at 6 and 10 h after treatment with actinomycin D and cycloheximide, respectively, than in cells transfected with the SD 3'-UTR construct. Higher luciferase activity was detected in monkey cells transfected with a vector containing the SD 3'-UTR inserted 3' to the luciferase gene compared with a luciferase AS 3'-UTR construct. Vector constructs, each containing one of two AU-rich sequence elements (AREs) from within the SD 3'-UTR sequence inserted 3' to the luciferase gene, were active in monkey and human cells; an ARE 5' to the SD 3'-UTR sequence was not. Engineered mutations of AUUUA motifs within the active AREs rendered them inactive in luciferase assays. The experiments demonstrate that two AREs within the 562 bp, missing in the SD 3'-UTR of TCR mRNA in SLE T cells, positively regulate transcription, stability, and translation and that their absence explains decreased TCR chain expression and abnormal T cell function in SLE. Profiling Lyme Arthritis
Infection with Borrelia burgdorferi causes severe arthritis in C3H mice and C57BL/6 mice lacking IL-10 (IL-10–/– B6) but only mild disease in wild-type B6 mice. Gene expression profiling and RT-PCR in this mouse model of Lyme arthritis by Crandall et al. (p. 7930 ) revealed similar bacterial loads in joint tissues from all strains 1 week postinfection (p.i.) and equivalent leukocyte recruitment at 2 weeks p.i. Expression of genes responsive to IFN or linked to IFN induction and regulation was greatly increased at 1 week p.i. in C3H and IL-10–/– B6, but not in B6, mice. Genes involved in epidermal differentiation, cell adhesion, and cell-cell interaction or wound repair had increased expression from 1 to 4 weeks p.i. in B6 mice but reduced expression in the other two strains. Expression of chemokines and genes associated with host defense increased in all strains by 2 weeks p.i. Genes involved in activating chondrocytes and bone formation were up-regulated at 4 weeks p.i. in C3H mice, and transcripts for matrix metalloproteases and tissue inhibitor of matrix metalloprotease had different expression profiles among the three mouse strains. This global gene expression analysis provides information about genes involved in disease development in this mouse model of Lyme arthritis.
CCR4 in Innate Immunity
Mice deficient in chemokine receptor CCR4 are more resistant to lethal LPS challenge than wild-type controls. To understand the resistance mechanism, Ness et al. (p. 7531
) challenged mice with a pathogenic strain of Escherichia coli. At 4 h after infection, CCR4–/– mice had elevated levels of peritoneal IL-10 and serum CCL2 compared with wild-type controls; at 24 h, mutant mice had fewer bacteria and lower IL-10, CCL2, and CCL3 levels than wild-type animals. Only CCR4–/– mice had elevated levels of mRNAs for TLRs 2, 4, 6, and 9 and for a mediator of Th2 responses of alternatively activated macrophages in CD11b+ cells recruited to the peritoneal cavity by i.p. injection of LPS. CCR4–/– macrophages secreted more cytokines characteristic of alternatively activated macrophages before and after LPS challenge than wild-type cells. Minimal NF-
B nuclear localization but enhanced JNK and p38 MAPK activation occurred in untreated CCR4–/– vs wild-type peritoneal macrophages; LPS treatment activated NF-B minimally but JNK and p38 MAPK significantly in the CCR4–/– cells. Almost no induction of NF-B pathway components occurred in LPS-treated CCR4–/– macrophages. The authors propose that increased resistance of CCR4–/– mice to LPS challenge is conferred by macrophages with higher TLR2 and TLR4 expression and a cytokine/chemokine profile characteristic of an alternatively activated phenotype accompanied by altered signaling pathways.
Manipulating Ag Immunodominance
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-chain usage between CD8+ T cells from wild-type and mutant mice. The authors present a quantitative model to explain how changes in Ag presentation and/or CD8+ T cell repertoire shape immunodominance patterns and can influence vaccination strategies. IL-27 Signals by Two Pathways
Participation of IL-27, a novel member of the IL-6/IL-12 family, is required for early regulation of Th1 cell and inflammatory responses. The Yoshimoto laboratory demonstrated that IL-27 polarizes Th1 cells through STAT1 and ICAM-1/LFA-1 in the absence of IL-12. In a continuation of those studies, Owaki et al. (p. 7579
) measured reduced IL-27-induced Th1 differentiation in stimulated T-box expressed in T cells (T-bet)-deficient CD4+ T cells compared with wild-type cells; reduction was noted in stimulated wild-type, and further reduction in T-bet–/–, cells treated with anti-ICAM-1/LFA-1 Abs. IL-27 induced p38 MAPK and ERK1/2 phosphorylation in the stimulated T cells, whereas IL-12 activated only p38 MAPK. Specific inhibitors of the two kinases did not suppress ICAM-1 expression on IL-27-activated wild-type cells; however, anti-ICAM-1/LFA-1 Abs suppressed IL-27-induced activation of ERK1/2, but not p38 MAPK, and reduced Th1 differentiation. Activation of only ERK1/2 was abolished in IL-27-treated STAT1–/– T cells. Transcription of a molecule that mediates p38 MAPK activation was enhanced in IL-27-treated wild-type cells and in cells deficient for ICAM-1/LFA-1, any of the above signaling molecules, or several transcription factors. Up-regulation of IL-12R2 surface expression occurred in IL-27-treated wild-type cells with or without the phosphorylation inhibitors but was lower in T-bet–/– cells or in wild-type cells treated with anti-ICAM-1/LFA-1 Abs. The authors demonstrate that IL-27 induction of Th1 differentiation involves both p38 MAPK/T-bet and ICAM-1/LFA-1/ERK1/2 pathways; only the first pathway is activated by IL-12.
Ringing in Th2 Cell Differentiation
Nakayama’s group demonstrated a prominent role for GATA3 protein in Th2 cell differentiation. In Hosokawa et al. (p. 7656 ), the same group investigated the severe combined immunodeficiency that develops in mice deficient in individual components of the Polycomb repressive complex 1 involved in histone ubiquitination. They found that generation of IL-4-producing cells cultured under Th2 and neutral conditions was enhanced among mouse CD4+ T cells infected with a retrovirus vector containing Polycomb gene bmi-1 (B lymphoma Moloney murine leukemia virus insertion region). Those Th2 cells had higher levels of GATA3 protein and Th2 cytokines after restimulation. Stabilization of GATA3 protein by wild-type Bmi-1 protein, demonstrated by cycloheximide treatment and pulse-chase experiments in T cells infected with the wild-type bmi-1 vector, was accompanied by decreased GATA3 ubiquitination. Tagged GATA3 and tagged Bmi-1 were coimmunoprecipitated from cells overexpressing both proteins. Reduced Th2 cell differentiation, less Bmi-1/GATA3 association, and no decrease in GATA3 ubiquitination compared with controls were seen in cells infected with a Bmi-1 protein mutant lacking the Ring finger domain needed to mediate protein-protein interactions. GATA3 ubiquitination and instability were increased in bmi-1–/– vs wild-type Th2 cells. The experiments demonstrate that Bmi-1 regulates Th2 cell differentiation via Ring finger interaction with GATA3 protein to stabilize it.
IDO-Resistant RA T Cells
Kynurenine, a tryptophan catabolite generated by IDO released from dendritic cells (DCs), induces apoptosis of autoreactive T cells. Impaired IDO-mediated tryptophan metabolism has been noted in several experimental autoimmune disease models. Zhu et al. (p. 8226
) detected high mRNA and protein expression of IDO in DCs from joint synovial fluid of rheumatoid arthritis (RA) patients and higher kynurenine levels in their culture medium compared with DCs from healthy controls. An IDO inhibitor enhanced proliferation of allogeneic healthy and RA PBLs induced by synovial fluid IDO+ RA DCs but not that induced by IDO– peripheral blood DCs; the inhibitor had no effect on RA synovial fluid T cell proliferation. Transcription of tryptophanyl-tRNA synthetase (TTS), which increases intracellular tryptophan stores, was elevated in RA synovial fluid T cells compared with PBLs from RA or healthy donors. The IDO inhibitor enhanced IDO+ RA DC-induced proliferation and apoptosis of RA T cells expressing low, but not high, levels of TTS. An increase in TTS levels in healthy or RA PBLs induced by RA synovial fluid was blocked by anti-IFN-
and/or anti-TNF-
mAbs. The authors show that inflammatory cytokines in RA synovial fluid increase TTS expression in autoreactive RA T cells to render them resistant to IDO-mediated apoptosis.
Novel Transgenic Rabbit Model
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Summaries written by Dorothy L. Buchhagen, Ph.D.
Related articles in The JI:
mRNA Are Regulated by the Adenosine-Uridine-Rich Elements in Splice-Deleted 3' Untranslated Region of -Chain
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