Lung allograft rejection has been associated with autoimmune CD4+ T cell responses to type V collagen (col(V)). The induction of oral tolerance to this Ag can prevent the rejection of lung allografts with minor histoincompatibility; however, it is not known whether this method can induce tolerance to fully MHC-incompatible grafts. Yamada et al. (p. 237) found that col(V)-induced oral tolerance alone could not prevent the rejection of fully incompatible lungs in a rat model but could enhance low-dose cyclosporine (CsA)-mediated suppression of alloimmunity to allow graft tolerance. This tolerance was not due to the systemic induction of regulatory T cells but was associated with up-regulated expression of Foxp3 and IL-10 and down-regulation of IFN-γ within the graft. In vitro analysis of direct allorecognition between donor APCs and host T cells indicated that col(V) + CsA treatment suppressed the expression of IFN-γ and IL-17A by the T cells and up-regulated the production of IL-10 by donor alveolar macrophages. Col(V) + CsA treatment also suppressed the recruitment of host-derived macrophages to the graft by reducing MCP-1 levels in the bronchoalveolar fluid. CsA-associated toxicity could be avoided in allograft recipients with this strategy, because it enables the use of a lower dose of CsA combined with the prevention of autoimmune responses to col(V).

Antineoplastic chemotherapeutic agents at conventional doses can suppress dendritic cell (DC) function or indirectly activate DCs through the release of Ag and “danger signals” from dying cells. Recent data suggested that very low, noncytotoxic doses of chemotherapy might directly modulate DC activity, leading Shurin et al. (p. 137) to assess the effects of different classes of antineoplastic agents on DC Ag-presenting activity. Many common chemotherapeutic drugs were found to increase Ag presentation by DCs when tested in very low concentrations. This effect was found, in many cases, to involve the augmentation of all three signals important for T cell activation. That is, several of the chemotherapeutic agents up-regulated the expression of Ag-processing machinery components and MHC class II (leading to signal 1), costimulatory molecules (signal 2), and IL-12 (signal 3). Analysis of DCs generated from IL-12-deficient mice indicated that the increased expression of IL-12 was directly related to the ability of some, but not all, of the agents to augment Ag presentation. Thus, DC function can be modulated via different mechanisms by different types of noncytotoxic chemotherapy, and this chemomodulation could be used to augment the efficacy of antitumor DC vaccines.

Since the identification of the inflammatory Th17 subset of T cells, intense investigation has focused on the regulation of these cells’ development and function. TGF-β is required for Th17 cell differentiation, but it is not clear how this cytokine chooses between promoting Th17 differentiation via induction of the transcription factor RORγt and regulatory T cell (Treg) differentiation via induction of Foxp3. Qin et al. (p. 97) hypothesized that TGF-β might inhibit suppressor of cytokine signaling 3 (SOCS3), which would relieve STAT3 from inhibition and enhance Th17 development. Indeed, TGF-β inhibited IL-6- and IL-21-induced SOCS3 expression, leading to enhanced and prolonged STAT3 activation that promoted Th17 cell differentiation. Small interfering RNA-mediated inhibition of SOCS3 partially compensated for the action of TGF-β in Th17 development and also enhanced IL-6-mediated inhibition of Foxp3 expression, suggesting a mechanism by which TGF-β could tip the Th17/Treg balance toward Th17 development. Blockade of Smad-dependent signaling through TGFβRI partially inhibited IL-17 production in Th17-promoting cultures, suggesting that both Smad-dependent and independent pathways were involved in TGF-β-mediated Th17 differentiation. These data begin to clarify the signaling pathways TGF-β may use to promote the development of multiple T cell lineages.

The Src homology 2-containing inositol 5′-phosphatase (SHIP1) is expressed in all hematopoietic cell lineages and acts as an inhibitor of immune receptor-mediated PI3K signaling, leading to suppression of the activation, proliferation, and/or survival of immune cells. SHIP1 represses mast cell cytokine production and degranulation in vitro, but its role in mast cells in vivo is not known. Haddon et al. (p. 228) therefore analyzed the effects of SHIP1 deficiency on mast cell function. SHIP1-deficient mice (Ship1−/−) have been reported to exhibit chronic inflammation, which the authors found included mast cell hyperplasia in multiple tissues. Compared with wild-type controls, Ship1−/− mice also had increased serum levels of IL-5, IL-6, and TNF and suffered a more severe course of passive systemic anaphylaxis. To determine whether these effects were due to mast cell-specific expression of SHIP1, the authors reconstituted mast cell-deficient mice with Ship1−/− or Ship1+/+ mast cells. Mice reconstituted with the Ship1−/− cells demonstrated mast cell hyperplasia, increased levels of IL-6 and TNF, and augmented allergic airway inflammation compared with mice reconstituted with wild-type mast cells, suggesting that the mast cell defects observed in Ship1−/− mice were indeed caused by mast cell-specific SHIP1 expression. Thus, SHIP1 is a repressor of mast cell homeostasis and activity in vivo.

Lymphocyte migration on the endothelium involves integrin-mediated adhesion of the cell’s leading edge to the endothelial cell surface. Conformational changes regulate integrin binding, but it is not known how these alterations occur during lymphocyte polarization and migration. Hyun et al. (p. 359) therefore developed a novel method of dynamic fluorescence resonance energy transfer (FRET) measurement in total internal reflection fluorescence (TIRF) microscopy to analyze the activation of integrin VLA-4 during T cell migration on VCAM-1. Although VLA-4 was distributed over the entire cell surface, activated VLA-4 was found to be specifically localized to the leading edge. An antagonist that selectively bound to activated VLA-4 was therefore able to inhibit T cell migration on a VCAM-1 + CXCL12-coated surface by specifically binding to the leading edge of the cells. At this leading edge, activated Rap1, which regulates VLA-4 activation, and CXCR4 colocalized with VLA-4. These data indicate that VLA-4 is required for T cell migration on VCAM-1 and provide support for the hypothesis that activated integrins preferentially localize to the leading edge of migrating cells.

Inflammatory bowel disease (IBD) involves mucosal CD4+ T cell-mediated inflammation that is regulated via mechanisms that are not fully understood. The costimulatory CD27:CD70 interaction is important for T cell expansion and survival, although its role for CD4+ T cells is less clear than it is for CD8+ T cells. CD70 is tightly regulated in most cell types but is constitutively expressed on a population of APCs in the intestinal lamina propria. This observation led Manocha et al. (p. 270) to address the function of the CD27:CD70 interaction in two mouse models of colitis. Transfer of CD27-deficient CD4+ T cells into Rag-1−/− mice or transfer of wild-type cells into mice treated with anti-CD70 Ab resulted in significantly ameliorated disease and reduced inflammatory cytokine production compared with those in untreated recipients of wild-type T cells. Anti-CD70 could not only block the induction of colitis but could also reverse established disease in this model. Reduced colitis was also observed in a trinitrobenzene sulfonic acid (TNBS)-mediated model following anti-CD70 treatment. However, blocking this costimulatory pathway did not alter the course of an innate immune model of colitis. The CD27:CD70 interaction therefore appears to be important for CD4+ T cell activation and consequent intestinal inflammation, and blockade of this pathway may represent a novel approach for IBD therapy.

No effective vaccine has been developed against visceral leishmaniasis, which is second only to malaria as a cause of parasite-induced deaths worldwide. In this issue, Samant et al. (p. 470) developed a novel DNA vaccine against Leishmania donovani and tested its efficacy in golden hamsters, which recapitulate the features of human visceral leishmaniasis more accurately than do mice. Leishmania species produce proteophosphoglycans (PPGs), mucin-like glycoproteins that play important roles in parasite virulence. The authors cloned the N-terminal domain of the L. donovani ppg gene, which contains many antigenic determinants, into an expression vector and then vaccinated hamsters with this construct. Following L. donovani challenge, vaccinated animals had nearly undetectable parasite loads and survived for at least 6 mo, whereas control animals died within 2–3 mo. Vaccination with ppg induced a delayed-type hypersensitivity response and L. donovani-specific lymphoproliferation, as well as elevated levels of IgG2. In addition, the vaccine induced NO production and a Th1 cytokine profile consisting of IFN-γ, TNF-α, and IL-12. In contrast, IL-4, IL-10, and TGF-β were up-regulated in control animals, but not by ppg immunization. The protection against L. donovani offered by this vaccine in hamsters offers hope that similar protection could be generated in humans.

Epstein-Barr virus (EBV) and CMV persistently infect the majority of people but are usually kept in a latent state by the immune response. To address how CD8+ T cells may protect against viral reactivation, Iancu et al. (p. 319) analyzed the EBV- and CMV-specific TCR clonotypes present in persistently infected healthy donors in relation to T cell differentiation. Four discrete subpopulations of virus-specific effector and effector memory T cells were identified based on the expression of CD45RA and CD28. Within these populations, the EBV-specific repertoire was more diverse than was the CMV-specific repertoire, but in both cases early- and late-differentiated cells expressed the same EBV- or CMV-specific TCRs, suggesting linear differentiation of virus-specific T cells. Some virus-specific clonotypes increased in frequency with differentiation whereas others decreased, suggesting in vivo selection of dominant CD8+ T cell responses. Interestingly, the TCR composition of each virus-specific subset remained remarkably stable over a period of four years. The late-differentiated T cells tended to be less dependent on CD8 binding than were the early-differentiated cells, but all CMV-specific clonotypes demonstrated similar functional avidities. Thus, a complex system of CD8+ T cell selection determines the composition of the immune response to persistent viral infections, and further understanding of this selection process may inform future strategies to combat infection.

Summaries written by Jennifer Hartt Meyers, Ph.D.