Tissue macrophages comprise a heterogeneous group of cell types differing in location, surface markers and function1. Red pulp macrophages are a distinct splenic subset involved in removing senescent red blood cells2. Transcription factors such as PU.1 and C/EBPα play general roles in myelomonocytic development3,4, but the transcriptional basis for producing tissue macrophage subsets remains unknown. Here we show that Spi-C, a PU.1 related transcription factor, selectively controls the development of red pulp macrophages. Spi-C is highly expressed in red pulp macrophages, but not monocytes, dendritic cells or other tissue macrophages. Spi-C−/− mice exhibit a cell-autonomous defect in the development of red pulp macrophages that is corrected by retroviral Spi-C expression in bone marrow cells, but have normal monocyte and other macrophage subsets. Red pulp macrophages highly express genes involved in capturing circulating hemoglobin and iron regulation. Spi-C−/− mice show normal trapping of red blood cells in the spleen, but fail to phagocytose these red blood cells efficiently, and develop an iron overload localized selectively to splenic red pulp. Thus, Spi-C controls development of red pulp macrophages required for red blood cell recycling and iron homeostasis.

Human pandemic H1N1 2009 influenza virus rapidly infected millions worldwide and was associated with significant mortality. Antiviral drugs that inhibit influenza virus replication are the primary therapy used to diminish disease; however, there are two significant limitations to their effective use: ( i ) antiviral drugs exert selective pressure on the virus, resulting in the generation of more fit viral progeny that are resistant to treatment; and ( ii ) antiviral drugs do not directly inhibit immune-mediated pulmonary injury that is a significant component of disease. Here we show that dampening the host's immune response against influenza virus using an immunomodulatory drug, AAL-R, provides significant protection from mortality (82%) over that of the neuraminidase inhibitor oseltamivir alone (50%). AAL-R combined with oseltamivir provided maximum protection against a lethal challenge of influenza virus (96%). Mechanistically, AAL-R inhibits cellular and cytokine/chemokine responses to limit immunopathologic damage, while maintaining host control of virus replication. With cytokine storm playing a role in the pathogenesis of a wide assortment of viral, bacterial, and immunologic diseases, a therapeutic approach using sphingosine analogs is of particular interest.

Calcineurin is required for B cell receptor (BCR)-induced proliferation of mature B cells. Paradoxically, loss of NFAT transcription factors, themselves calcineurin targets, induces hyperactivity, which suggests that calcineurin targets other than NFAT are required for BCR-induced proliferation. Here we demonstrate a function for the calcineurin-regulated transcription factor Mef2c in B cells. BCR-induced calcium mobilization was intact after Mef2c deletion, but loss of Mef2c caused defects in B cell proliferation and survival after BCR stimulation in vitro and lower T celldependent antibody responses and germinal center formation in vivo. Mef2c activity was specific to BCR stimulation, as Toll-like receptor and CD40 signaling induced normal responses in Mef2c-deficient B cells. Mef2c-dependent targets included the genes encoding cyclin D2 and the prosurvival factor Bcl-x L . Our results emphasize an unrecognized but critical function for Mef2c in BCR signaling.B cell receptor (BCR) signaling coordinates the development, maintenance, activation and tolerance of B cells. BCR engagement induces the phosphorylation of tyrosine residues in immunoreceptor tyrosine-based activation motifs of immunoglobulin-α and immunoglobulin-β by Src family kinases 1 . Subsequently, other kinases and adaptor molecules orchestrate signaling cascades that eventually activate transcription factors required for the proliferation, survival and differentiation of B cells, including those of the NFAT, AP-1 and NF-κB families 2-5 . BCR engagement can induce opposite outcomes depending on the stage of B cell development 6 . In mature B cells, BCR signaling induces proliferation, affinity maturation and class-switch recombination during T cell-dependent responses and ultimately drives the differentiation of B cells into memory cells and antibody-secreting plasma cells 7 . Alternatively, in immature B cells in the bone marrow and recent bone marrow emigrants in

The emergence of human-transmissible H5N1 avian influenza viruses poses a major pandemic threat. H5N1 viruses are thought to be highly genetically diverse both among and within hosts, but the effects of this diversity on viral replication and transmission are poorly understood. Here we use deep sequencing to investigate the impact of within-host viral variation on adaptation and transmission of H5N1 viruses in ferrets. We show that although within-host genetic diversity in hemagglutinin (HA) increases during replication in inoculated ferrets, HA diversity is dramatically reduced upon respiratory droplet transmission, where infection is established by only 1–2 distinct HA segments from a diverse source virus population in transmitting animals. Moreover, minor HA variants present in as little as 5.9% of viruses within the source animal become dominant in ferrets infected via respiratory droplets. These findings demonstrate that selective pressures acting during influenza virus transmission among mammals impose a significant bottleneck.

Acute thrombocytopenia is a recognized complication of treatment with GPIIb/IIIa inhibitors whose cause is not yet known. We studied 9 patients who developed severe thrombocytopenia (platelets less than 25 × 109/L) within several hours of treatment with the GPIIb/IIIa inhibitors tirofiban (4 patients) and eptifibatide (5 patients). In each patient, acute-phase serum contained a high titer (range, 1:80-1:20 000) IgG antibody that reacted with the glycoprotein IIb/IIIa complex only in the presence of the drug used in treatment. Four patients had been previously treated with the same drug, but 5 had no known prior exposure. Pretreatment serum samples from 2 of the latter patients contained drug-dependent antibodies similar to those identified after treatment. No tirofiban- or eptifibatide-dependent antibodies were found in any of 100 randomly selected healthy blood donors, and only 2 of 23 patients receiving tirofiban or eptifibatide who did not experience significant thrombocytopenia had extremely weak (titer, 1:2) tirofiban-dependent antibodies. In preliminary studies, evidence was obtained that the 9 antibodies recognize multiple target epitopes on GPIIb/IIIa complexed with the inhibitor to which the patient was sensitive, indicating that they cannot all be specific for the drug-binding site. The findings indicate that acute thrombocytopenia after the administration of tirofiban or eptifibatide can be caused by drug-dependent antibodies that are “naturally occurring” or are induced by prior exposure to drug. These antibodies may be human analogs of mouse monoclonal antibodies that recognize ligand-induced binding sites (LIBS) induced in the GPIIb/IIIa heterodimer when it reacts with a ligand-mimetic drug.

Individuals infected with O157 infection presenting with a more severe illness were at an increased risk of developing HUS. The use of bactericidal antibiotics, particularly β-lactams, to treat O157 infection was associated with the subsequent development of HUS.

Immune thrombocytopenia induced by quinine and many other drugs is caused by antibodies that bind to platelet membrane glycoproteins (GPs) only when the sensitizing drug is present in soluble form. In this disorder, drug promotes antibody binding to its target without linking covalently to either of the reacting macromolecules by a mechanism that has not yet been defined. How drug provides the stimulus for production of such antibodies is also unknown. We studied 7 patients who experienced severe thrombocytopenia after ingestion of quinine. As expected, drug-dependent, platelet-reactive antibodies specific for GPIIb/IIIa or GPIb/IX were identified in each case. Unexpectedly, each of 6 patients with GPIIb/ IIIa-specific antibodies was found to have a second antibody specific for drug alone that was not platelet reactive. Despite recognizing different targets, the 2 types of antibody were identical in requiring quinine or desmethoxy-quinine (cinchonidine) for reactivity and in failing to react with other structural analogues of qui-

We report an outbreak of canine distemper virus (CDV) infection among endangered giant pandas (Ailuropoda melanoleuca). Five of six CDV infected giant pandas died. The surviving giant panda was previously vaccinated against CDV. Genomic sequencing of CDV isolated from one of the infected pandas (giant panda/SX/2014) suggests it belongs to the Asia-1 cluster. The hemagglutinin protein of the isolated virus and virus sequenced from lung samples originating from deceased giant pandas all possessed the substitutions V26M, T213A, K281R, S300N, P340Q, and Y549H. The presence of the Y549H substitution is notable as it is found at the signaling lymphocytic activation molecule (SLAM) receptor-binding site and has been implicated in the emergence of highly pathogenic CDV and host switching. These findings demonstrate that giant pandas are susceptible to CDV and suggest that surveillance and vaccination among all captive giant pandas are warranted to support conservation efforts for this endangered species.