Binding of Ag to the BCR induces signal transduction and BCR internalization, leading to Ag processing and presentation. Previous studies have proposed a role for the actin cytoskeleton in linking BCR signaling to BCR-mediated Ag transport. The actin-binding protein 1 (Abp1) can interact simultaneously with the cytoskeleton and signaling molecules and is involved in TCR signaling, so Onabajo et al. (p. 6685 ) assessed the role of Abp1 in BCR activity. Abp1 deficiency reduced BCR-mediated Ag uptake and transport, resulting in impaired Ag processing and presentation. Overexpression studies implicated the Src homology 3 (SH3) domain of Abp1 in this process. BCR stimulation induced recruitment of Abp1 to the plasma membrane and its colocalization with the BCR, and this redistribution required both Abp1 tyrosine phosphorylation and involvement of the actin cytoskeleton. Finally, Abp1 was found to constitutively interact via its SH3 domain with the proline-rich domain of dynamin 2, which is a GTPase involved in endocytosis. These data demonstrate a role for Abp1 in coupling BCR signaling to Ag processing and presentation by its simultaneous interaction with BCR signaling, cytoskeletal, and endocytic components.

Although adoptive cell transfer of tumor-infiltrating lymphocytes has proven effective in melanoma treatment, it is difficult to isolate tumor-specific T cells in most other cancers. It has been suggested that adoptive transfer of autologous T cells transduced with tumor-specific TCRs could circumvent this problem. To evaluate the viability of this approach, Coccoris et al. (p. 6536 ) measured the long-term persistence and functionality of TCR-transduced T cells in a mouse model. The authors transferred T cells transduced with an OVA-specific TCR (OT-1) into wild-type recipients and found that these cells persisted and remained responsive to Ag for at least 6 mo. The transferred cells also mounted a secondary response to OVA following a heterologous prime-boost challenge, indicating that TCR-transduced T cells have the capacity to survive and remain functional long-term in vivo. To determine whether these cells could also successfully respond to a self-Ag, the authors performed similar experiments in RIP-OVAhigh transgenic mice. OT-1 TCR-transduced T cells transferred into this self-tolerant setting could also persist and mount effective secondary responses to Ag. Examination of the TCR-transduced T cells after secondary challenge demonstrated that they remained polyclonal, indicating that their effectiveness was not due to the preferential outgrowth of one or more T cell clones. These encouraging data suggest that TCR-transduced T cells could be useful tools for cancer therapy.

The mouse Igκ gene locus contains several cis-acting regulatory elements involved in transcription, gene rearrangement, and somatic hypermutation (SHM). It is not yet clear what role the downstream enhancer Ed plays in Igκ regulation, so Xiang et al. (p. 6725 ) created mice with a homozygous deletion of this region (Ed−/−). These mice showed no defect in the numbers of splenic marginal zone, follicular, or transitional B cells nor in plasma cell differentiation. However, the mice had reduced Igκ+ B cells and serum Igκ chains and correspondingly increased Igλ+ B cells and serum Igλ chains compared with wild-type controls. Analysis of Igκ mRNA expression indicated that Igκ transcription was reduced in Ed−/− resting B cells and in B cells responding to T cell-dependent stimulation. However, Igκ gene rearrangement occurred normally in Ed−/− mice, indicating that this enhancer does not regulate Vκ-Jκ recombination. Finally, the authors determined that SHM of the Igκ locus was decreased in Ed−/− germinal center B cells in Peyer’s patches. This clear determination of Ed activity advances understanding of the complex transcriptional control of the Igκ locus.

Although the costimulatory ligands CD80 and CD86 have traditionally been considered functionally similar, recent studies have indicated that CD80 may be a preferential ligand for CTLA-4, whereas CD86 may preferentially bind to CD28. Perez et al. (p. 6566 ) assessed the effects of dominant costimulation through CD80 and found that an interaction between CD80 and CTLA-4 induced the differentiation of TGF-β1+ adaptive regulatory T cells (Treg). In vitro analysis of T cell activation demonstrated that blockade of CD86 or the use of CD86-deficient APCs induced hyporesponsive T cells with reduced proliferation, reduced IFN-γ and IL-2 production, and increased IL-10 production. The hyporesponsive CD4+ T cells produced in conditions of dominant CD80 costimulation were shown to be adaptive Treg able to suppress T cell proliferation via TGF-β1. These Treg were independent of CD4+CD25+ natural Treg and required an interaction between CD80 and CTLA-4 for their induction. Adoptive transfer of CD86−/− dendritic cells into NOD mice resulted in a delay in diabetes onset, a reduction in insulitis severity, and an increase in T cells producing TGF-β1 and IL-10 compared with controls. This study reveals functional differences between the B7 molecules and indicates that CD80:CTLA-4 interaction in the absence of CD86 can induce the development of adaptive Treg.

Signaling through the TCR complex can lead to several different functional outcomes, but it is not clear how T cell signaling cascades are organized to allow this single receptor to mediate multiple processes. Wang et al. (p. 6703 ) therefore compared TCR signaling following stimulation conditions leading to either proliferation or apoptosis in mature CD8+ T cells. TCR stimuli that caused apoptosis induced strong but transient phosphorylation of PKB/Akt and ERK1/2, whereas activating stimuli induced weaker but sustained phosphorylation of these kinases. Apoptosis-inducing stimuli also caused stronger activation of ZAP-70, LAT, PLC-γ1, and DAG and a stronger calcium flux compared with proliferation-inducing stimuli. It has been shown that during thymic negative selection, ERK1/2 is strongly but transiently activated and is targeted to the plasma membrane, whereas during positive selection ERK1/2 is activated in a weak, sustained manner and is targeted to the Golgi apparatus. The authors observed similarly selective subcellular localization of ERK1/2 in mature CD8+ T cells, in that apoptosis-inducing signals transiently targeted this kinase to the plasma membrane, whereas activating signals led to ERK1/2 localization in the recycling endosomes. Taken together, these data define qualitative and quantitative differences in TCR signaling that selectively induce distinct T cell responses.

The promoter region of the macrophage-specific gene encoding the colony-stimulating factor 1 receptor (csf1r) lacks conventional proximal promoter elements such as TATA boxes and Sp1 sites. To better understand how transcription of this gene is initiated, Hume et al. (p. 6733 ) undertook an in-depth analysis of the promoter region of csf1r and of the proteins able to bind to it. Using cap analysis of gene expression (CAGE), the authors precisely localized the transcriptional start site (TSS) of csf1r and went on to identify conserved sequence motifs in the proximal promoter that were occupied in a highly sequence-specific manner. The proteins binding to these motifs were identified as FUS/TLS and Ewing sarcoma protein (EWS), both of which are mainly known as RNA-binding proteins. EWS, but not FUS/TLS, was found to specifically bind to the csf1r TSS in unstimulated primary macrophages. By creating mutant csf1r reporter plasmids, the authors sought to determine the promoter sequence necessary for EWS binding and to measure EWS activity but found, surprisingly, that this protein did not function as a traditional transcriptional activator or repressor. This work thus begins to elucidate novel mechanisms by which the transcription of mammalian genes may be initiated or regulated.

Respiratory syncytial virus (RSV) pathogenesis involves the production of proinflammatory mediators by airway epithelial cells (AEC). RSV infection activates NFκB and triggers the production of reactive oxygen species (ROS), both of which promote the inflammatory response. Fink et al. (p. 6911 ) sought to identify the source of ROS in infection with the paramyxoviruses RSV and Sendai virus (SeV) and to determine ROS involvement in NFκB regulation. First, the authors found that viral infection induced the phosphorylation of p65 at Ser536, which was required for full NFκB transactivation activity. Treatment of an AEC cell line with diphenyleneiodonium inhibited p65Ser536 phosphorylation and subsequent NFκB activity, implicating an NADPH oxidase in this process. Experiments using RNA interference and a luciferase reporter system then identified NOX2 as an NADPH oxidase subunit required for RSV- and SeV-induced NFκB activation. The mechanism of NOX2-mediated NFκB regulation was found to involve phosphorylation of IκBαSer32 and p65Ser536. NOX2-dependent NFκB regulation was also observed in human primary AEC, indicating the physiological relevance of this study. These data define a novel pathway of ROS-mediated NFκB activation in viral infection and identify NOX2 as a potential therapeutic target to limit RSV-induced inflammation.

It has been suggested that autoimmune disorders share common genetic determinants and pathogenic mechanisms. Mattapallil et al. (p. 6751 ) set out to identify non-MHC chromosomal regions that regulate susceptibility to experimental autoimmune uveitis (EAU) and to determine whether these regions colocalize with quantitative trait loci (QTL) of other autoimmune diseases. Analysis of a large population of F2 generation rats derived from EAU-resistant (F344) and susceptible (LEW) strains led to the identification of six regions, named Eau4–Eau9, which were associated with variations in disease susceptibility, and epistatic interactions between these loci influenced EAU severity. These regions, located on rat chromosomes 2, 3, 7, 10, and 19, colocalized with QTL associated with other autoimmune diseases, including models of Type I diabetes, rheumatoid arthritis, and multiple sclerosis. The syntenic chromosomal regions in human and mouse were also associated with susceptibility to multiple autoimmune diseases. This study identified markers for uveitis susceptibility and demonstrated interactions between QTL involved in autoimmune disease development. The data also support the idea that EAU development may share mechanisms with other autoimmune disorders.

Summaries written by Jennifer Hartt Meyers, Ph.D.