Interferons (IFNs) are cytokines produced by host cells in response to the infection with pathogens. By binding to the corresponding receptors, IFNs trigger different pathways to block intracellular replication and growth of pathogens and to impede the infection of surrounding cells. Due to their key role in host defense against viral infections, as well as for clinical therapies, the IFN responses and regulation mechanisms are well studied. However, studies of type I IFNs have mainly focused on alpha interferon (IFN-α) and IFN-β subtypes. Knowledge of IFN-κ and IFN-ω is limited. Moreover, most studies are performed in humans or mouse models but not in the original host of zoonotic pathogens. Bats are important reservoirs and transmitters of zoonotic viruses such as lyssaviruses. A few studies have shown an antiviral activity of IFNs in fruit bats. However, the function of type I IFNs against lyssaviruses in bats has not been studied yet. Here, IFN-κ and IFN-ω genes from the European serotine bat, Eptesicus serotinus , were cloned and functionally characterized. E. serotinus IFN-κ and IFN-ω genes are intronless and well conserved between microchiropteran species. The promoter regions of both genes contain essential regulatory elements for transcription factors. In vitro studies indicated a strong activation of IFN signaling by recombinant IFN-ω, whereas IFN-κ displayed weaker activation. Noticeably, both IFNs inhibit to different extents the replication of different lyssaviruses in susceptible bat cell lines. The present study provides functional data on the innate host defense against lyssaviruses in endangered European bats. IMPORTANCE We describe here for the first time the molecular and functional characterization of two type I interferons (IFN-κ and -ω) from European serotine bat ( Eptesicus serotinus ). The importance of this study is mainly based on the fact that very limited information about the early innate immune response against bat lyssaviruses in their natural host serotine bats is yet available. Generally, whereas the antiviral activity of other type I interferons is well studied, the functional involvement of IFN-κ and -ω has not yet been investigated.

A role for GH and IGF-I in the modulation of the immune system has been under discussion for decades. Generally, GH is considered a stimulator of innate immune parameters in mammals and teleost fish. The stimulatory effects in humans as well as in bony fish often appear to be correlated with elevated endocrine IGF-I (liver-derived), which has also been shown to be suppressed during infection in some studies. Nevertheless, data are still fragmentary. Some studies point to an important role of GH and IGF-I particularly during immune organ development and constitution. Even less is known about the potential relevance of local (autocrine/paracrine) IGF-I within adult and developing immune organs, and the distinct localization of IGF-I in immune cells and tissues of mammals and fish has not been systematically defined. Thus far, IGF-I has been localized in different mammalian immune cell types, particularly macrophages and granulocytes, and in supporting cells, but not in T-lymphocytes. In the present study, we detected IGF-I in phagocytic cells isolated from rainbow trout head kidney and, in contrast to some findings in mammals, in T-cells of a channel catfish cell line. Thus, although numerous analogies among mammals and teleosts exist not only for the GH/IGF-system, but also for the immune system, there are differences that should be further investigated. For instance, it is unclear whether the primarily reported role of GH/IGF-I in the innate immune response is due to the lack of studies focusing on the adaptive immune system, or whether it truly preferentially concerns innate immune parameters. Infectious challenges in combination with GH/IGF-I manipulations are another important topic that has not been sufficiently addressed to date, particularly with respect to developmental and environmental influences on fish growth and health.

Bats are found to be the natural reservoirs for many emerging viruses. In most cases, severe clinical signs caused by such virus infections are normally not seen in bats. This indicates differences in the virus-host interactions and underlines the necessity to develop natural host related models to study these phenomena. Due to the strict protection of European bat species, immortalized cell lines are the only alternative to investigate the innate anti-virus immune mechanisms. Here, we report about the establishment and functional characterization of Myotis myotis derived cell lines from different tissues: brain (MmBr), tonsil (MmTo), peritoneal cavity (MmPca), nasal epithelium (MmNep) and nervus olfactorius (MmNol) after immortalization by SV 40 large T antigen. The usefulness of these cell lines to study antiviral responses has been confirmed by analysis of their susceptibility to lyssavirus infection and the mRNA patterns of immune-relevant genes after poly I:C stimulation. Performed experiments indicated varying susceptibility to lyssavirus infection with MmBr being considerably less susceptible than the other cell lines. Further investigation demonstrated a strong activation of interferon mediated antiviral response in MmBr contributing to its resistance. The pattern recognition receptors: RIG-I and MDA5 were highly up-regulated during rabies virus infection in MmBr, suggesting their involvement in promotion of antiviral responses. The presence of CD14 and CD68 in MmBr suggested MmBr cells are microglia-like cells which play a key role in host defense against infections in the central nervous system (CNS). Thus the expression pattern of MmBr combined with the observed limitation of lyssavirus replication underpin a protective mechanism of the CNS controlling the lyssavirus infection. Overall, the established cell lines are important tools to analyze antiviral innate immunity in M. myotis against neurotropic virus infections and present a valuable tool for a broad spectrum of future investigations in cellular biology of M. myotis.