Rickettsia felis, the etiologic agent of spotted fever, is maintained in cat fleas by vertical transmission and resembles other tick-borne spotted fever group rickettsiae. In the present study, we utilized an Ixodes scapularisderived tick cell line, ISE6, to achieve isolation and propagation of R. felis. A cytopathic effect of increased vacuolization was commonly observed in R. felis-infected cells, while lysis of host cells was not evident despite large numbers of rickettsiae. Electron microscopy identified rickettsia-like organisms in ISE6 cells, and sequence analyses of portions of the citrate synthase (gltA), 16S rRNA, Rickettsia genus-specific 17-kDa antigen, and spotted fever group-specific outer membrane protein A (ompA) genes and, notably, R. felis conjugative plasmids indicate that this cultivatable strain (LSU) was R. felis. Establishment of R. felis (LSU) in a tick-derived cell line provides an alternative and promising system for the expansion of studies investigating the interactions between R. felis and arthropod hosts.Spotted fever group rickettsiae (SFGR) are obligately intracellular gram-negative bacteria that are typically associated with ticks, with one exception being the etiologic agent of flea-associated spotted fever, Rickettsia felis, described predominately in the cat flea, Ctenocephalides felis. There are a growing number of reports implicating R. felis as a human pathogen. Serological analysis and PCR amplification of rickettsial DNA in human samples coupled with clinical manifestations, including fever and maculopapular rash, characterize rickettsiosis (reviewed in reference 24). In colonized cat fleas, vertical transmission of R. felis is thought to be the primary route of maintenance (3, 43); however, the acquisition mechanism of R. felis by vertebrates and uninfected fleas in nature is unknown. Studies on the ecology of R. felis identified a role for opossums in the transmission cycle (6,32,45). Additionally, a role for companion animals, rodents, and, specifically, their fleas as the potential source of human exposure has been suggested (2,8,27).The relatively recent identification and characterization of R. felis yielded novel aspects for the genus Rickettsia. A rickettsia-like organism, first observed by electron microscopy in the midgut epithelial cells of colonized adult cat fleas, was designated the "ELB agent" after the source of the fleas, the Elward Laboratory (El Soquel, CA) flea colony (1). Amplification of rickettsial genes encoding citrate synthase (gltA) and the genus-specific 17-kDa antigen confirmed the presence of rickettsiae in the Elward Laboratory colony (3), and the name R. felis was proposed (10). Subsequent amplification of the genes encoding the 17-kDa antigen and the 190-kDa antigen (ompA) from a colony of fleas maintained at Louisiana State University (LSU) (Baton Rouge, LA) confirmed the molecular characterization of the bacteria and further classified R. felis as an SFGR (7). Although attempts were unable to produce a sustained culture of either the ELB ...

Activation of astrocytes and microglia and the production of proinflammatory cytokines and chemokines are often associated with virus infection in the CNS as well as a number of neurological diseases of unknown etiology. These inflammatory responses may be initiated by recognition of pathogen-associated molecular patterns (PAMPs) that stimulate TLRs. TLR7 and TLR8 were identified as eliciting antiviral effects when stimulated by viral ssRNA. In the present study, we examined the potential of TLR7 and/or TLR8 agonists to induce glial activation and neuroinflammation in the CNS by intracerebroventricular inoculation of TLR7 and/or TLR8 agonists in newborn mice. The TLR7 agonist imiquimod induced astrocyte activation and up-regulation of proinflammatory cytokines and chemokines, including IFN-β, TNF, CCL2, and CXCL10. However, these responses were only of short duration when compared with responses induced by the TLR4 agonist LPS. Interestingly, some of the TLR7 and/or TLR8 agonists differed in their ability to activate glial cells as evidenced by their ability to induce cytokine and chemokine expression both in vivo and in vitro. Thus, TLR7 stimulation can induce neuroinflammatory responses in the brain, but individual TLR7 agonists may differ in their ability to stimulate cells of the CNS.

No abstract

Summary Equine influenza virus remains a major health concern for the equine industry in spite of ongoing vaccination programmes. Previous work has shown that the immune system of horses can be affected by strenuous exercise. The possible adverse consequence of exercise‐induced alterations in lymphocyte responses measured in vitro was unknown. Here we demonstrate that subjecting vaccinated ponies to a 5 day strenuous exercise programme results in a significant suppression of their T cell‐mediated immune response to equine influenza virus as measured by decreased lymphoproliferation and gamma interferon production measured in vitro. These same ponies also demonstrated increased susceptibility to influenza disease following a challenge exposure to the same strain of virus. Rested ponies that had received the same vaccine and challenge were completely protected from disease. Our results demonstrate that exercise‐induced suppression of the equine immune response to influenza virus can be associated with an increased susceptibility to disease.

Toll-like receptor 7 (TLR7) recognizes guanidine-rich single-stranded (ss) viral RNA and is an important mediator of peripheral immune responses to several ssRNA viruses. However, the role that TLR7 plays in regulating the innate immune response to ssRNA virus infections in specific organs is not as clear. This is particularly true in the central nervous system (CNS) where microglia and astrocytes are often the first cells responding to virus infection instead of dendritic cells. In the current study, we examined the mechanism by which TLR7 contributes to ssRNA virus-induced neuroinflammation using a mouse model of polytropic retrovirus infection. The authors found that TLR7 was necessary for the early production of certain cytokines and chemokines, including CCL2 and tumor necrosis factor (TNF) and was also involved in the early activation of astrocytes. However, TLR7 was not necessary for cytokine production and astrocyte activation at later stages of infection and did not alter viral pathogenesis or viral replication in the brain. This suggests that other pathogen recognition receptors may be able to compensate for the lack of TLR7 during retrovirus infection in the CNS.