No abstract

Staphylococcus aureus can cause difficult-to-treat chronic infections. We recently reported that S. aureus chronic infection was associated with a profound inhibition of T cell responses. In this study, we investigated the mechanisms responsible for the suppression of T cell responses during chronic S. aureus infection. Using in vitro coculture systems, as well as in vivo adoptive transfer of CFSE-labeled OT-II cells, we demonstrated the presence of immunosuppressive mechanisms in splenocytes of S. aureus–infected mice that inhibited the response of OT-II cells to cognate antigenic stimulation. Immunosuppression was IL-10/TGF-β independent but required cell–cell proximity. Using DEREG and Foxp3gfp mice, we demonstrated that CD4+CD25+Foxp3+ regulatory T cells contributed, but only to a minor degree, to bystander immunosuppression. Neither regulatory B cells nor tolerogenic dendritic cells contributed to immunosuppression. Instead, we found a significant expansion of granulocytic (CD11b+Ly6G+Ly6Clow) and monocytic (CD11b+Ly6G−Ly6Chigh) myeloid-derived suppressor cells (MDSC) in chronically infected mice, which exerted a strong immunosuppressive effect on T cell responses. Splenocytes of S. aureus–infected mice lost most of their suppressive activity after the in vivo depletion of MDSC by treatment with gemcitabine. Furthermore, a robust negative correlation was observed between the degree of T cell inhibition and the number of MDSC. An increase in the numbers of MDSC in S. aureus–infected mice by adoptive transfer caused a significant exacerbation of infection. In summary, our results indicate that expansion of MDSC and, to a minor degree, of regulatory T cells in S. aureus–infected mice may create an immunosuppressive environment that sustains chronic infection.

Canine distemper virus (CDV) is a pantropic morbillivirus with a worldwide distribution, which causes fatal disease in dogs. Affected animals develop dyspnea, diarrhea, neurological signs and profound immunosuppression. Systemic CDV infection, resembling distemper in domestic dogs, can be found also in wild canids (e.g. wolves, foxes), procyonids (e.g. raccoons, kinkajous), ailurids (e.g. red pandas), ursids (e.g. black bears, giant pandas), mustelids (e.g. ferrets, minks), viverrids (e.g. civets, genets), hyaenids (e.g. spotted hyenas), and large felids (e.g. lions, tigers). Furthermore, besides infection with the closely related phocine distemper virus, seals can become infected by CDV. In some CDV outbreaks including the mass mortalities among Baikal and Caspian seals and large felids in the Serengeti Park, terrestrial carnivores including dogs and wolves have been suspected as vectors for the infectious agent. In addition, lethal infections have been described in non-carnivore species such as peccaries and non-human primates demonstrating the remarkable ability of the pathogen to cross species barriers. Mutations affecting the CDV H protein required for virus attachment to host-cell receptors are associated with virulence and disease emergence in novel host species. The broad and expanding host range of CDV and its maintenance within wildlife reservoir hosts considerably hampers disease eradication.

Osteomyelitis is a serious bone infection typically caused by Staphylococcus aureus. The pathogenesis of osteomyelitis remains poorly understood, mainly for lack of experimental models that closely mimic human disease. We describe a novel murine model of metastatic chronic osteomyelitis initiated after intravenous inoculation of S. aureus microorganisms. The bacteria entered bones through the bloodstream and, after an acute phase with progressive growth (first 2 weeks after infection), they remained at constant numbers for up to 56 days (chronic phase). Clinical signs of illness and systemic inflammation were apparent only during the acute phase. Bone destruction and remodeling processes were readily detectable by magnetic resonance and X-ray imaging 3 weeks after infection, and high levels of bone deformation were observed during the chronic phase. Histological examination of infected bones demonstrated suppurative inflammation with foci of intense bacterial multiplication and necrosis during acute infection and osteoclastic resorption accompanied by new woven bone formation during chronic infection. Transmission electron microscopy revealed S. aureus microorganisms forming microcolonies within the nonmineralized collagen matrix or located intracellularly within neutrophils. In summary, our mouse model of staphylococcal hematogenous osteomyelitis precisely reproduces most features of the human disease. Although the extent of lesions in the chronic phase was subject to variation, this model is ideal for testing and monitoring novel treatment modalities via noninvasive imaging.

Hepatitis C virus (HCV) continues to represent one of the most significant threats to human health. In recent years, HCV-related sequences have been found in bats, rodents, horses, and dogs, indicating a widespread distribution of hepaciviruses among animals. By applying unbiased high-throughput sequencing, a novel virus of the genus Hepacivirus was discovered in a bovine serum sample. De novo assembly yielded a nearly full-length genome coding for a polyprotein of 2,779 amino acids. Phylogenetic analysis confirmed that the virus represents a novel species within the genus Hepacivirus. Viral RNA screening determined that 1.6% (n ‫؍‬ 5) of 320 individual animals and 3.2% (

Virus-host interactions in the respiratory epithelium during long term influenza virus infection are not well characterized. Therefore, we developed an air-liquid interface culture system for differentiated porcine respiratory epithelial cells to study the effect of virus-induced cellular damage. In our well-differentiated cells, α2,6-linked sialic acid is predominantly expressed on the apical surface and the basal cells mainly express α2,3-linked sialic acid. During the whole infection period, release of infectious virus was maintained at a high titre for more than seven days. The infected epithelial cells were subject to apoptosis resulting in the loss of ciliated cells together with a thinner thickness. Nevertheless, the airway epithelium maintained trans-epithelial electrical resistance and retained its barrier function. The loss of ciliated cells was compensated by the cells which contained the KRT5 basal cell marker but were not yet differentiated into ciliated cells. These specialized cells showed an increase of α2,3-linked sialic acid on the apical surface. In sum, our results help to explain the localized infection of the airway epithelium by influenza viruses. The impairment of mucociliary clearance in the epithelial cells provides an explanation why prior viral infection renders the host more susceptible to secondary co-infection by another pathogen.

Streptococcus suis causes numerous diseases in pigs, most importantly, meningitis, arthritis, septicemia, and bronchopneumonia. One of the major problems in modern swine production is the lack of a vaccine protecting against more than one S. suis serotype. The objective of this study was to determine the protective efficacy of a serotype 2 murein-associated protein (MAP) fraction subunit vaccine in comparison to that of a bacterin against experimental challenge with serotype 2 (containing muramidase-released protein [MRP], extracellular factor, and suilysin [SLY]) and serotype 9 (containing MRP variant MRP* and SLY) strains. MAP was shown to include different surface-associated proteins, such as the MRP and surface antigen one (SAO) expressed by both pathotypes used for challenge. The results of this study demonstrated that the serotype 2 bacterin induced protective immunity against homologous challenge. In contrast, the protective efficacy of the MAP subunit vaccine was low, though MAP immunization resulted in high serum immunoglobulin G2 titers against MRP and SAO. Importantly, immunization with bacterin but not with MAP induced opsonizing antibody titers against the serotype 2 strain, and these antibody titers were found to correlate with protection. However, after absorption with a nonencapsulated isogenic mutant, the sera from bacterin-immunized piglets failed to facilitate neutrophil killing, indicating that antibodies directed against capsule may not have been essential for opsonophagocytosis. Furthermore, induction of opsonizing antibodies against serotype 9 was not detectable in the group receiving bacterin or in the group receiving the MAP vaccine. In agreement, protection against the heterologous serotype 9 strain was low in both groups. Thus, identification of an antigen protecting against these two important S. suis pathotypes remains an important goal of future studies.Streptococcus suis ranks among the five most important health challenges of pigs worldwide (11,12). It is associated with numerous diseases, such as meningitis, arthritis, serositis, and bronchopneumonia. S. suis isolates from diseased animals express a polysaccharide capsule which confers resistance to phagocytosis, as demonstrated for serotype 2 strains (21). Strains of various serotypes have been isolated from affected tissues. In Europe, serotype 2 and 9 strains are the most prevalent types isolated from infections. The 136-kDa muramidasereleased protein (MRP) and the 110-kDa extracellular factor (EF) are virulence-associated factors expressed only by virulent serotype 1 and 2 strains (22, 23). The majority of invasive serotype 9 isolates express a larger variant of MRP, termed MRP*, which shares high homology with the 136-kDa MRP protein of serotype 2 strains (20, 23).

Better understanding of the pathogenesis of spinal cord injury (SCI) is needed for the development of new therapeutic strategies. Spinal cord injury has been investigated in various rodent models, but extrapolation to humans requires the use of a large animal model that more closely mimics human SCI. Dogs frequently develop spontaneous SCI with features that bear a striking resemblance to the human counterpart. We investigated the temporal course of the immune response during naturally occurring canine SCI and in organotypic canine spinal cord slice cultures that are devoid of peripheral immune cells. By immunohistochemistry, the inflammatory response in subacute canine SCI was largely restricted to resident immune cells as demonstrated by activation of major histocompatibility complex class II-expressing microglia/macrophages. By quantitative polymerase chain reaction, there was parallel upregulation of proinflammatory cytokine gene expression (i.e. of interleukin 6 [IL-6] and IL-8 with a trend toward upregulation of tumor necrosis factor) in acute canine SCI. Expression of neuroprotective cytokines (e.g. IL-10) remained unchanged, and transforming growth factor β upregulation was delayed. In organotypic spinal cord slices, there was similar activation of major histocompatibility complex class II-positive microglia and prolonged upregulation of inflammatory cytokines, indicating that resident rather than infiltrating cells play major roles in the postinjury immune response. Thus, canine SCI represents a bridge between rodent models and human SCI that may be relevant for clinical and preclinical treatment studies.