Depending on the cytokine environment, IL-27, which is closely related to IL-12, interacts with its receptor WSX-1 to promote or inhibit Th1 cell inflammatory responses. However, the role of IL-27/WSX-1 interactions in Th2 cell responses is unknown. Artis et al. (p. 5626 ) found increased levels of IL-27 mRNA in mesenteric lymph nodes of C57BL/6 mice infected 1 and 2 wk earlier with the gastrointestinal helminth parasite Trichuris muris. WSX-1−/− mice cleared all larval parasites by day 14 postinfection and produced higher levels of Th2 cytokines (IL-4, IL-5, and IL-13) than infected wild-type mice. Mutant mice also demonstrated intestinal goblet cell hyperplasia, increased mucin production, higher numbers of intestinal mast cells, and degranulation products. All of these type 2 cytokine-dependent responses were significantly reduced in infected WSX-1−/− animals that had received anti-IL-4 mAb. WSX-1−/− mice had a greater mast cell response in vivo to intradermal DNP challenge 24 h after DNP-IgE priming compared with wild-type controls. T cells from infected wild-type and mutant animals produced equivalent amounts of IFN-γ following in vitro challenge 14 days postinfection. Treatment of wild-type mice with anti-IL-12 and anti-IFN-γ mAbs did not promote a WSX-1−/−-like response to T. muris infection. CD4+ T cells from uninfected mutant animals had enhanced proliferative responses and production of IL-5 and IL-13 upon secondary stimulation under Th2-polarizing conditions than wild-type cells. The data demonstrate that IL-27 and WSX-1 interact in an IFN-γ-independent manner to inhibit mucosal Th2 immune responses.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory neural disease often studied as an animal model of human multiple sclerosis. To define an agent that is neuroprotective in both diseases, Aktas et al. (p. 5794 ) studied a polyphenol, (−)-epigallocatechin-3-gallate (EGCG), found in green tea. Treatment of SJL/J mice with 60 μg of EGCG twice daily, beginning at the time of immunization with an EAE-inducing protein, resulted in reduced inflammatory lesions in the brain stem and spinal cord, and lower clinical scores compared with vehicle-treated mice. The proliferative response and TNF-α production of draining lymph node T cells from EGCG-treated immunized animals were reduced compared with controls. The in vitro expansion of myelin basic protein-specific human CD4+ T cells in response to peptide-loaded APCs or to anti-CD3/CD28 activation also was inhibited. EGCG reduced expression of cyclin-dependent kinase 4 and blocked proteasome activity, resulting in IκB-α accumulation and in inhibition of NF-κB activation in CD4+ T cells. EGCG-treated EAE mice had fewer apoptotic neurons in brain tissue sections than control mice, and living organotypic brain slice cultures treated with a neurotoxin were protected against neuronal cell death by prior treatment with EGCG. However, no accumulation of IκB-α was seen in brain tissue; rather, EGCG prevented the formation of reactive oxygen species in neurons treated with an inhibitor of glutathione synthetase. The data demonstrate that EGCG, the major polyphenolic compound of green tea, has both neuroprotective and anti-inflammatory activities in EAE.

Although GATA-3 is known to stimulate T cell-specific expression of IL-13, factors that induce IL-13 expression in mast cells are not defined. On p. 5564 , Masuda et al. show that several murine mast cell lines produced IL-13 in response to PMA/ionomycin stimulation; one line also responded to stimulation with LPS or by IgE cross-linking. The responsive DNA sequences in the IL-13 promoter were mapped to nt −106 to −94 using deletion mutants in luciferase reporter assays. Mutations within the defined region reduced GATA binding to a faster migrating constitutively appearing complex as determined by EMSA and reduced AP-1 binding to a slower migrating complex that appeared after stimulation of transfected mast cells. Cotransfection of a wild-type IL-13 promoter construct with a dominant negative c-jun mutant reduced levels of IL-13 promoter luciferase activity. Transcription of the wild-type IL-13 promoter construct in stimulated cells was increased in a dose-dependent manner by cotransfection with GATA-1 or GATA-2 expression plasmids. This transactivation did not occur with the AP-1 binding site mutant or in the presence of the c-jun mutant. Analyses of IL-13 promoter-binding proteins showed that GATA proteins were constitutive in the nuclei but that c-fos and c-jun appeared only after stimulation of the cells; GATA-1 copurified with AP-1. GATA deletion mutants defined three regions of protein interaction with c-jun. The results show that AP-1 and GATA cooperate to transactivate the IL-13 gene in mast cells and that AP-1 is indispensable for this activity.

In their prior studies on negative selection of autoreactive B cells, Caton and colleagues found persistence of B cells capable of primary and memory responses in mice (HA104) transgenically expressing an influenza virus protein (PR8 HA) under the control of a viral promoter. In Guay et al. (p. 5485 ), the same group developed a strain of transgenic mice (HACII) that expressed PR8 HA as a membrane-bound Ag driven by a MHC class II promoter. Wild-type and transgenic mice were immunized with a virus containing a single amino acid change in PR8 HA. PR8 HA-specific IgG, but not IgM, Ab-secreting cells were significantly reduced in both HACII and HA104 mice compared with wild-type controls; all strains reacted with the mutated PR8 HA. One-half of PR8 HA-specific IgG-secreting B cell hybridomas from wild-type mice, but none from either transgenic mouse strain, used the VκC12 variable region. IgM-secreting hybridomas from transgenic mice were half VκC4 and half VκC12 clonotypes. Purified IgGs from all mice had higher reactivities against PR8 HA than a control Ab, and IgMs from all mice had lower reactivities. Mutant virus challenge of animals immunized with the mutant virus induced IgG Ab-secreting splenocytes specific for the mutated epitope in HACII mice; only wild-type and HA104 animals also produced PR8 HA-specific IgG Ag-secreting cells. SCID mice injected with a mixture of wild-type and HACII splenocytes and primed 1 day later with the mutated virus generated a memory response after challenge that was specific for the mutated epitope. The data show that B cells, autoreactive for a membrane-bound Ag, are excluded from memory formation in a dominant manner.

Allergens, including bacterial products, initiate the inflammation of atopic dermatitis, although the mechanism by which they act is unknown. Pivarcsi et al. (p. 5810 ) determined chemokine expression profiles specific for a variety of skin diseases by quantitative real-time PCR analyses and found significant CCL18 up-regulation in human lesional atopic skin compared with normal skin or lesional skin of other inflammatory skin diseases. Immunohistochemically, CCL18 was localized in dendritic cells (DCs) evenly dispersed within the dermal layer and clustered in perivascular pockets. In vitro, IFN-γ and IL-4 stimulated cultured human primary keratinocytes and dermal fibroblasts to produce high levels of CCL18 mRNA. A variety of microbial-derived compounds or CD40L induced expression of CCL18 mRNA and protein in monocytes; Langerhans-type DCs and interstitial DCs constitutively expressed high levels of CCL18 mRNA and protein. Exposure to house dust mite allergens induced CCL18 mRNA expression in skin of atopic dermatitis patients or in single-cell suspensions from their lesions. A Staphylococcus aureus superantigen also induced CCL18 expression in skin and in PBMCs isolated from atopic dermatitis patients. NiSO4 patch treatment of nonatopic Ni-sensitized individuals resulted in CCL18 mRNA induction in skin cells, whereas a chemical irritant did not. The authors conclude that CCL18, up-regulated in DCs of atopic patients by a variety of allergens, initiates and amplifies atopic skin inflammation.

Sztein and coworkers have shown that CD8+ T cells are important in the host response to infection with Salmonella enterica serovar Typhi (S. Typhi). In the paper on p. 5852 , Salerno-Goncalves et al. followed up on their previous work to determine the mechanism by which CD8+ T cells kill S. Typhi-infected PBMCs from human volunteers. Agents that induced degranulation of CTL inhibited the lytic activity, whereas anti-Fas mAb had no effect. Released granzyme B was detected in cocultures of CTL with S. Typhi-infected cells. Cytotoxic activity was blocked by an inhibitor of HLA class I Ag processing, but not by an inhibitor of HLA class II Ag processing. S. Typhi-specific CTL killed all S. Typhi-infected B cell lines whether allogeneic or autologous with regard to HLA class I alleles, and cytotoxic activity was blocked by mAb to CD3, CD8, or HLA-class I. The effector cell population was identified as CD3+CD8+CD56 T cells by cell sorting. HLA-E expression intracellularly and on the surface of uninfected or S. Typhi-infected T cells or of macrophages from uninfected volunteers was up-regulated after 60-min incubation with CTL effector cells; anti-HLA-E mAbs partially blocked the up-regulation. Increased HLA-E surface expression was seen with S. Typhi-infected B cells incubated with each of several S. Typhi peptides, and the peptide-loaded infected B cells induced increased release of granzyme-B and IFN-γ from effector cells. The experiments identify a new CD3+CD8+CD56 CTL effector that recognizes human S. Typhi-infected target cells in a nonclassical HLA-E-restricted manner.

Peptides that bind to MHC class I molecules average 8–10 aa in length. It is expected that longer peptides will have lower binding affinity to HLA molecules. Probst-Kepper et al. (p. 5610 ) obtained a 1.5-Å resolution crystal structure of the human MHC class I molecule HLA-B*3501 in complex with a 14-aa-long peptide derived from an alternative reading frame of the human M-CSF. The peptide was anchored to HLA-B*3501 by 3 aa at its N terminus and 2 aa at its C terminus; the central portion looped out between the two α helices of the HLA groove compared with a control 9-aa peptide bound to HLA-B*3501. Substitution of alanine for the proline at aa 2 in the 14-mer reduced flexibility of the looped portion, altered the positioning of the peptide within the binding groove in regions critical for TCR contact, and decreased recognition by a CTL clone specific for the M-CSF peptide. Proline to alanine substitution at both aa 2 and aa 9 had more drastic consequences, i.e., almost complete loss in flexibility of the looped region, further divergence in position within the binding groove, and abrogation of recognition by the CTL. The length of the CDR3s of the M-CSF peptide-specific CTL clone were 1 and 2 aa longer than CDR3s of TCRs recognizing peptides 8–10 aa in length. The analysis shows that the minimum requirement for high-affinity MHC binding is proper N- and C-terminal anchoring and suggests that CTLs would recognize longer peptides in clinical therapies.

Summaries written by Dorothy L. Buchhagen, Ph.D.