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Mast cells (MCs) are powerful immune cells that mature in the peripheral tissues from bone marrow (BM)-derived mast cell progenitors (MCp). Accumulation of MCs in lung compartments where they are normally absent is thought to enhance symptoms in asthma. The enrichment of lung MCs is also observed in mice subjected to models of allergic airway inflammation. However, whether other types of lung inflammation trigger increased number of MCp, which give rise to MCs, is unknown. Here, mouse-adapted H1N1 influenza A was used as a model of respiratory virus infection. Intranasal administration of the virus induced expression of VCAM-1 on the lung vascular endothelium and an extensive increase in integrin β7hi lung MCp. Experiments were performed to distinguish whether the influenza-induced increase in the number of lung MCp was triggered mainly by recruitment or in situ cell proliferation. A similar proportion of lung MCp from influenza-infected and PBS control mice were found to be in a proliferative state. Furthermore, BM chimeric mice were used in which the possibility of influenza-induced in situ cell proliferation of host MCp was prevented. Influenza infection in the chimeric mice induced a similar number of lung MCp as in normal mice. These experiments demonstrated that recruitment of MCp to the lung is the major mechanism behind the influenza-induced increase in lung MCp. Fifteen days post-infection, the influenza infection had elicited an immature MC population expressing intermediate levels of integrin β7, which was absent in controls. At the same time point, an increased number of toluidine blue+ MCs was detected in the upper central airways. When the inflammation was resolved, the MCs that accumulated in the lung upon influenza infection were gradually lost. In summary, our study reveals that influenza infection induces a transient accumulation of lung MCs through the recruitment and maturation of MCp. We speculate that temporary augmented numbers of lung MCs are a cause behind virus-induced exacerbations of MC-related lung diseases such as asthma.

Mast cells are known to have a detrimental impact on a variety of pathological conditions. There is therefore an urgent need of developing strategies that limit their harmful effects. The aim of this study was to accomplish this by developing a means of inducing mast cell apoptosis. The strategy was to identify novel compounds that induce mast cell apoptosis by permeabilization of their secretory lysosomes (granules). As a candidate, we assessed mefloquine, an anti-malarial drug that has been proposed to have lysosome-permeabilizing activity. Mefloquine was added to mast cells and administered in vivo, followed by assessment of the extent and mechanisms of mast cell death. Mefloquine was cytotoxic to murine and human mast cells. Mefloquine induced apoptotic cell death of wild-type mast cells whereas cells lacking the granule compounds serglycin proteoglycan or tryptase were shown to undergo necrotic cell death, the latter finding indicating a role of the mast cell granules in mefloquine-induced cell death. In support of this, mefloquine was shown to cause compromised granule integrity and to induce leakage of granule components into the cytosol. Mefloquine-induced cell death was refractory to caspase inhibitors but was completely abrogated by reactive oxygen species inhibition. These findings identify mefloquine as a novel anti-mast cell agent, which induces mast cell death through a granule-mediated pathway. Mefloquine may thus become useful in therapy aiming at limiting harmful effects of mast cells.

This study aimed at identifying all of the type I interferon (IFN) genes of the horse and at monitoring their expression in equine cells on in vitro induction. We identified 32 putative type I IFN loci on horse chromosome 23 and an unplaced genomic scaffold. A phylogentic analysis characterized these into 8 different type I IFN classes, that is, putative functional genes for 6 IFN-α, 4 IFN-β, 8 IFN-ω (plus 4 pseudogenes), 3 IFN-δ (plus 1 pseudogene), 1 IFN-κ and 1 IFN-e, plus 1 IFN-ν pseudogene, and 3 loci belonging to what has previously been called IFN-αω. Our analyses indicate that the IFN-αω genes are quite distinct from both IFN-α and IFN-ω, and we refer to this type I IFN as IFN-μ. Results from cell cultures showed that leukocytes readily expressed IFN-α, IFN-β, IFN-δ, IFN-μ, and IFN-ω mRNA on induction with, for example, live virus; while fibroblasts only expressed IFN-β mRNA on stimulation. IFN-κ or IFN-e expression was not consistently induced in these cell cultures. Thus, the equine type I IFN family comprised 8 classes, 7 of which had putative functional genes, and mRNA expression of 5 was induced in vitro. Moreover, a relatively low number of IFN-α subtypes was found in the horse compared with other eutherian mammals.

Bovine respiratory syncytial virus (BRSV) is one of the major causes of bovine respiratory disease worldwide. In order to study the molecular epidemiology of the virus, samples from 30 BRSV outbreaks in cattle herds located in different parts of Sweden were collected from 2007 to 2011. The samples were analyzed by PCR, and the glycoprotein (G) gene was sequenced. BRSV was detected in outbreaks of respiratory disease in both dairy and feedlot herds most often during the winter period but also during the summer months (May to August). This indicates that circulation of the virus between herds occurs throughout the year. Comparative sequence analysis revealed a high degree (more than 94.5%) of sequence identity among the collected strains. Phylogenetic analysis showed that 29 out of the 30 strains formed a unique clade. Identical sequences found in herds sampled within a few months' time suggested that these herds were part of a common transmission chain. One strain from a single outbreak in a herd in southern Sweden clustered with Danish strains and showed a distant relationship to the rest of the Swedish strains. Further studies are highly warranted to clarify the inter-herd transmission routes of BRSV. Such knowledge is essential for the control of the spread of this virus between herds, regions and even countries.