Research articles

Bali Pulendran and his colleagues explore ways that signaling through different pathogen receptors can program dendritic cells (DCs) to orchestrate inflammatory or tolerogenic immune responses. The yeast component zymosan triggers signaling through both Toll-like receptor 2 (TLR2) and the C-type lectin dectin-1. In the absence of TLR2, zymosan induces proinflammatory responses through dectin-1. But TLR2 triggering induces DCs to form the vitamin A–metabolizing enzyme Raldh2. The DCs can then form retinoic acid that acts in an autocrine manner on the DCs, programming them for the induction of regulatory T cell responses.

Bone is resorbed by osteoclasts, and too much activity by these cells leads to disease, such as osteoporosis. Here Kyoji Ikeda and colleagues show that the combined action of iron uptake and a key transcription factor involved in mitochondrial biogenesis are required for the proper functioning of these cells and that in cases of increased bone loss, iron chelation may be beneficial by inhibiting these cells.

Hypoxia promotes tumor growth by stimulating angiogenesis, glycolysis, resistance to apoptosis and cell invasion. Wang et al. now report that hypoxia also increases the duration of growth factor signaling in tumor cells. They show that hypoxia-inducible factor downregulates the expression of an effector of early endosome fusion, slowing the endocytic recycling of epidermal growth factor receptor and thereby extending its activation and potential to enhance tumor cell proliferation and survival (pages 246–247).

During autophagy, cytosolic proteins and damaged organelles are delivered via autophagosomes to lysosomes, where they are degraded before presentation at the cell surface. Agents that induce autophagy have previously been shown to boost antigen presentation in vitro. Here Chinnaswamy Jagannath and colleagues show in mice that autophagy can be exploited to boost the efficacy of a dendritic cell vaccine for Mycobacterium tuberculosis.

In this issue, three reports show that Kindlin-3 is crucial for activation of multiple classes of integrins in several types of hematopoietic cells. In mice, Kindlin-3 was previously shown to be important for platelet activation and blood clotting, and Moser et al. now show its importance in leukocytes for adhesion to the endothelium. In humans, Svensson et al. and Malinin et al. show that mutation of the gene encoding Kindlin-3 is associated with a disease syndrome involving severe bleeding, infection and osteopetrosis, which Malinin et al. showed could be corrected by bone marrow transplantation (pages 249–250, 300–305 and 313–318).

Interleukin-10 is known to dampen immune responses and contribute to the persistence of chronic viruses and parasites. Thomas Braciale and his colleagues show in mice that the anti-inflammatory cytokine is produced, along with proinflammatory cytokines, by effector CD4⁺ and CD8⁺ T cells during an acute virus infection of the lung, thereby helping to regulate the extent of inflammatory lung damage in response to the virus.

In this issue, three reports show that Kindlin-3 is crucial for activation of multiple classes of integrins in several types of hematopoietic cells. In mice, Kindlin-3 was previously shown to be important for platelet activation and blood clotting, and Moser et al. now show its importance in leukocytes for adhesion to the endothelium. In humans, Svensson et al. and Malinin et al. show that mutation of the gene encoding Kindlin-3 is associated with a disease syndrome involving severe bleeding, infection and osteopetrosis, which Malinin et al. showed could be corrected by bone marrow transplantation (pages 249–250, 300–305 and 306–312).

Kindlin-3 interacts with β₁ and β₃ integrins on platelets, and Kindlin-3–deficient mice have defects in platelet activation and blood clotting. Moser et al. now show that these mice also have defects in β₂ integrin activation on leukocytes, leading to severely compromised leukocyte adhesion to the endothelium. The combined platelet and leukocyte defects of these mice resemble those seen in individuals with the leukocyte adhesion deficiency syndrome LAD-III. Other papers in this issue by Malinin et al. and Svensson et al. provide evidence that KINDLIN-3 dysfunction does indeed underlie this type of human disease syndrome (pages 249–250, 306–312 and 313–318).

Issue:Vaccines that induce T cell responses to simian immunodeficiency virus are able to reduce virus load in infected macaques. Such vaccines typically induce central memory T cells that must expand before gaining full antiviral functions. Picker and his colleagues show that a new replicating anti-SIV vaccine, based on the persistently infecting cytomegalovirus, which preferentially induces effector memory T cells in mucosal tissues, can reduce the likelihood that the macaques become infected in the first place (pages 244–246).

A research team led by Renier Brentjens offers a new approach to monitor in vivo trafficking of T cells by tagging them for bioluminescence imaging using a membrane-anchored form of the humanized Gaussia luciferase enzyme. The set-up provides a high bioluminescent signal and should be useful for studying in vivo T cell function in mouse models of disease investigating mouse or human primary T cells.

The first phase 2 gene therapy trial for HIV-1 has shown some promising signs. There's a long way to go before this would be a viable approach in people with HIV—this trial did not show a statistically significant difference in viral load at the primary end point–but other analyses did reveal that the gene therapy seemed to have a modest, but statistically significant, effect at reducing viral load in the treated subjects versus the placebo arm. The study also provides some clues about what to improve in the future.

Mark Tuszynski and his colleagues show that brain-derived neurotrophic factor is neuroprotective and can improve cognition in rodent and primate models of Alzheimer's disease.

Increased calcium levels in dystrophic muscle have damaging consequences. In this report, Bellinger et al. show that nitrosylation of the ryanodine receptor calcium channel, leading to calcium leak through the channel, is an underlying cause of increased calcium levels in the muscle of dystrophic mdx mice. Treatment of the mice with a compound that inhibits calcium leak increases their muscle function and physical activity, pointing to a potential new treatment for muscular dystrophy (pages 243–244).

Does Mycobacterium tuberculosis replicate in vivo, or does it persist in the host in a nonreplicating latent state? David Sherman and his colleagues have developed a technique to answer this question in mice and find that the mycobacteria do replicate in vivo. It is unknown whether these findings will hold true in other animals, particularly nonhuman primates, but this technique could be applied to study the in vivo replication of other persistent pathogens responsible for chronic infections.

In this report, Skokowa et al. delineate a new molecular pathway by which synthesis of the metabolite NAD⁺ through the action of the enzyme NAMPT promotes myeloid cell differentiation. The potential clinical relevance of this pathway was demonstrated by showing that administration of vitamin B3, a precursor to NAD⁺, increases neutrophil counts in healthy individuals, and that defective myeloid cell differentiation in individuals with congenital neutropenia can be rescued in vitro by administration of NAMPT.

Inflammation plays a detrimental role in ischemic stroke. Now, Roland Veltkamp and his colleagues show that endogenous immunomodulatory T regulatory cells play a key part to dampen inflammation after stroke.

After injury to the spinal cord, hemorrhages occur both near and far from the initial lesion. J. Marc Simard and his colleagues demonstrate that spinal cord injury induces expression of the channel Trpm4 on endothelial cells in the spinal cord, which leads to their fragmentation and the spread of the hemorrhage.

By capitalizing on copy number variation, Wu and his colleagues offer an approach for detecting cellular chimerism with fluorescent in situ hybridization probes that target polymorphic deletion loci. These probes can determine the fate of donor cells in situ, irrespective of gender, and should prove useful in understanding the dynamics of cellular chimerism after solid organ, bone marrow and hematopoietic stem cell transplantation.

TNF is a key pathogenic cytokine in sepsis. Oberdan Leo and colleagues show that production of TNF during sepsis is regulated by the coenzyme NAD and that inhibition of the enzyme NAMPT, which generates NAD from nicotinamide, can improve survival during sepsis in mice. NAD seems to act via sirtuin-6 to increase the translation of TNF.

Cerebral cavernous malformation (CCM) is a life-threatening disorder in which blood vessels in the brain dilate and frequently hemorrhage. Benjamin Kleaveland et al. now provide evidence that CCM arises from defects in a signaling pathway involving the KRIT1 and CCM2 intracellular proteins (which have been previously implicated in CCM) and the HEG1 receptor; this pathway acts in endothelial cells and is required for vascular integrity. The role of the CCM2 protein in the endothelium is also explored in another paper published in this issue of Nature Medicine, by Kevin Whitehead et al.