Establishment and characterization of murine macrophage-like cell lines following transformation with simian virus 40 DNA deleted at the origin of replication

The immortalisation of rat hepatocytes by transfection with SV40 sequences

Abbreviations EGTA - ethylene bis(oxyethylenenitrilo)-tetraacetic acid; F12 - Ham's F12; FBS - foetal bovine serum; HBSS - Hank's balanced salt solution; HDM - hormonally defined medium; HEPES - 4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid; NBS - new born calf serum; WME - Williams' medium E.

Characterization of an equine macrophage cell line: application to studies of EIAV infection

EIAV is a monocyte/macrophage tropic virus. To date, even though EIAV has been under investigation for numerous years, very few details have been elucidated about EIAV/macrophage interactions. This is largely due to the absence of an equine macrophage cell line that would support viral replication. Herein we describe the spontaneous immortalization and generation of a clonal equine macrophage-like (EML) cell line with the functional and immunophenotype characteristics of differentiated equine monocyte derived macrophage(s) (eMDM(s)). These cells possess strong non-specific esterase (NSE) activity, are able to phagocytose fluorescent bioparticles, and produce nitrites in response to LPS. The EML-3C cell line expresses the EIAV receptor for cellular entry (ELR1) and supports replication of the virulent EIAV(PV) biological clone. Thus, EML-3C cells provide a useful cell line possessing equine macrophage related properties for the growth and study of EIAV infection as well as of other equine macrophage tropic viruses.

Irf3 polymorphism alters induction of interferon beta in response to Listeria monocytogenes infection

Genetic makeup of the host plays a significant role in the course and outcome of infection. Inbred strains of mice display a wide range of sensitivities to Listeria monocytogenes infection and thus serve as a good model for analysis of the effect of genetic polymorphism. The outcome of L. monocytogenes infection in mice is influenced by the ability of this bacterium to induce expression of interferon beta mRNA, encoded in mouse by the Ifnb1 (interferon beta 1, fibroblast) gene. Mouse strains that lack components of the IFNβ signaling pathway are substantially more resistant to infection. We found that macrophages from the ByJ substrain of the common C57BL/6 inbred strain of mice are impaired in their ability to induce Ifnb1 expression in response to bacterial and viral infections. We mapped the locus that controls differential expression of Ifnb1 to a region on Chromosome 7 that includes interferon regulatory factor 3 (Irf3), which encodes a transcription factor responsible for early induction of Ifnb1 expression. In C57BL/6ByJ mice, Irf3 mRNA was inefficiently spliced, with a significant proportion of the transcripts retaining intron 5. Analysis of the Irf3 locus identified a single base-pair polymorphism and revealed that intron 5 of Irf3 is spliced by the atypical U12-type spliceosome. We found that the polymorphism disrupts a U12-type branchpoint and has a profound effect on the efficiency of splicing of Irf3. We demonstrate that a naturally occurring change in the splicing control element has a dramatic effect on the resistance to L. monocytogenes infection. Thus, the C57BL/6ByJ mouse strain serves as an example of how a mammalian host can counter bacterial virulence strategies by introducing subtle alteration of noncoding sequences.

Specific variances in an individual's DNA, known as genetic polymorphisms, can play a significant role in determining susceptibility to an infectious disease. To identify the genetic polymorphisms that are associated with resistance to the common human bacterial pathogen L. monocytogenes, we have carried out a series of genetic and molecular biology experiments using closely related strains of mice that are differentially susceptible to Listeria infection. Through this analysis, we have identified a spontaneous mutation in an intron of the Irf3 gene, which encodes a key transcription factor involved in innate immunity. This single nucleotide change affects the efficiency with which Irf3 mRNA is spliced, thus limiting the ability of bacteria to induce interferon beta expression in order to suppress innate immune defense. By analyzing this mutation, we found that processing of mouse Irf3 mRNA relies on an atypical U12 splicing mechanism that has been suggested to be a rate-limiting step in gene expression. Our findings not only provide an additional example of an important role of noncoding polymorphisms in control of gene function, but also demonstrate how such polymorphisms can fine tune innate immune response.