Molecular detection and identification of type I interferon mRNAs

Cocaine causes increased type I interferon secretion by both L929 cells and murine macrophages

Cocaine has been demonstrated to have a number of different effects on immune cell functions. We have reported alterations of cellular functions by macrophages (Mphi) exposed to cocaine in vitro, including the inhibition of mouse hepatitis virus replication. Here, we present evidence that cocaine stimulates the secretion of an antiviral product that is neutralized by anti-interferon (anti-IFN). A dose-dependent increase in the secretion of IFN by both Mphi and L929 cells incubated with cocaine, with a concomitant decrease in virus replication, is also reported. The increase in IFN secretion was most pronounced when cells were cultured in the presence of the IFN inducer poly(I.C). The effect of cocaine on IFN production was found to be primarily at the transcript level in both Mphi and L929 cells. These findings further support our previous research demonstrating an antiviral activity of cocaine in vitro. The relevance of this activity to viral infections in general remains to be determined.

In vivo expression of an interferon-alpha gene by intramuscular injection of naked DNA

Acid-stable type I interferons belong to a multigene family. The biologic relevance of each subtype in vivo remains unknown. We have developed an experimental model in which muscles were transfected in situ with naked DNA plasmids encoding an IFN transgene to assess the roles of individual IFN subtypes in vivo. Murine IFN-alpha 9 gene was subcloned into several mammalian expression vectors. Adult C57BL/6 mice were injected bilaterally in regenerating tibialis anterior muscles with naked DNA 5 days after muscle injury to enhance DNA uptake and expression. In the muscles of mice given the IFN-alpha 9 plasmid constructs, acid-stable IFNs were detected by bioassay using reduction in cytopathic effect of encephalomyocarditis virus-infected L929 cells. In these same muscles, IFN-alpha 9 transcripts were identified by RT-PCR, indicating that transcription had occurred. Acid-stable IFNs were detected from days 7 to 28 post-DNA inoculation. Furthermore, these proteins were found in the sera of DNA-inoculated mice. Control groups of mice given the blank expression vectors did not produce detectable IFNs in muscle or sera as determined by bioassay, nor were transcripts detected by RT-PCR. This approach now allows investigation of the effector function of individual subtypes in various murine disease models.

The in vivo expression patterns of individual type I interferon genes in murine cytomegalovirus infections

Type I interferon (IFN) family has more than 10 structurally related subtypes of alpha IFN (IFNA) genes and a single beta IFN (IFNB) gene. This study examined the expression of MuIFNA1, A4, A5, A6, A9 and MuIFNB mRNAs in the livers and spleens of MCMV-infected mice at 2, 4 and 6 h post infection. The three strains of inbred mice studied were C57BL/6, B6.C-H-28c and BALB/c. B6.C-H-28c strain is a congenic strain of C57BL/6 genomic background. Detection of the specific mRNAs was by an established semiquantitative procedure based on reverse transcription and PCR amplification followed by differential hybridization to specific oligonucleotides. Similar expression patterns of the type I IFN mRNAs were found in C57BL/6 and B6.C-H-28c strains of mice. However, when the genotype was significantly different (BALB/c), a different expression pattern of IFN mRNAs was seen. Differences in the expression patterns of the type I IFN mRNAs was also seen between the livers and spleens of a given mouse strain. Thus, the present study indicates that mouse genotype appears to be a major determinant of the subtype response pattern seen in vivo and that tissue-type can influence the subtype response pattern seen within a given mouse genotype.

The in vitro expression patterns of individual type I interferon genes in Newcastle disease virus infected murine splenocytes and fibroblasts

Murine type I interferon levels present in mice sera following Newcastle disease virus infections are influenced by the If-1 locus. Sera interferon levels in C57BL/6 mice (If-1h allele) are 10- to 15-fold higher than in BALB/c mice (If-1(1) allele). The B6.C-H-28c strain, which carries BALB/c If-1(1) allele on C57BL/6 genomic background, has low interferon levels in sera. This study examined the expression of interferon alpha 1, alpha 4, alpha 5, alpha 6, alpha 9 and beta mRNAs at 7 hr after Newcastle disease virus infection of primary cells (splenocytes and mouse embryo fibroblasts) from C57BL/6, B6.C-H-28c and BALB/c mouse genotypes. Total RNA from these cells was reverse transcribed and all known type I interferon subtypes were amplified. The products were identified by differential hybridization to a panel of subtype specific oligonucleotides. The results show that the pattern of interferon subtypes examined in splenocytes did not differ between If-1h and If-1(1) allele carrying C57BL mice. However, when the genotype was different (BALB/c splenocytes) the pattern of type I interferon mRNAs seen was altered. This genotype-dependent expression was also seen in newcastle disease virus infected fibroblasts. Within a given mouse strain, there were also differences in the subtype response patterns detected in fibroblasts compared with those seen in splenocytes. In conclusion, the present study indicates that mouse genotype appears to be a major determinant of the subtype response pattern seen and tissue specific pattern differences are present within a given mouse genotype.

Alpha/beta interferons increase host resistance to murine AIDS

Murine AIDS (MAIDS) is caused by a defective retrovirus present in the LP-BM5 murine leukemia virus mixture. Strains of inbred mice differ in resistance to MAIDS development; some are susceptible (e.g., C57BL/6), while others are resistant (e.g., CBA and B10.BR). As an early block to viral replication in resistant mice has been demonstrated previously by PCR studies, we postulated that alpha/beta interferons (IFN-alpha/beta) may be involved in resistance to MAIDS. Susceptible C57BL/6 mice infected with LP-BM5 were treated with IFN-alpha/beta or Newcastle disease virus. Newcastle disease virus induces high endogenous IFN-alpha/beta production in mice. Both treatments delayed the development of MAIDS, as assessed by splenomegaly and T- and B-cell proliferation. In addition, an IFN-alpha/beta response was detected by reverse transcription-PCR and dot blotting 3, 6, and 9 h after LP-BM5 infection in resistant mice but not in susceptible mice. These results suggest that the ability to produce IFN-alpha/beta in response to LP-BM5 infection may contribute to host resistance to MAIDS.

Differential expression patterns of type I interferon subtypes in mouse embryo fibroblasts: influence of genotype and viral inducer

Primary mouse embryo fibroblasts from 4 strains of mice (BALB/c, C57Bl/6, B6.C-H-28c and CBA) were infected with either Newcastle disease virus or murine cytomegalovirus. The time course of the total type I interferon response was assessed and the presence of individual subtypes determined. The total type I interferon produced was titrated using the cytopathic effect reduction assay and the relative levels of type I interferon subtypes expressed (alpha 1, alpha 4, alpha 5, alpha 6 and beta) were evaluated using a reverse transcription-polymerase chain reaction-based technique. In general, the patterns of type I interferon subtypes expressed appeared to be determined by the strain of mouse cells used rather than the inducing virus. However, the overall titre of type I interferons produced in response to a given virus was quite uniform across the strains of mice from which the mouse embryo fibroblasts were derived regardless of the subtype expression pattern. The latter observation fits the proposition that "cross-talk" or feedback between the type I interferon genes and their products is is occurring and that the inducer determines the level of response.