Taken together, these findings suggest that expression of human CD46 in mouse macrophages enhances production of IFN-/ in response to MV infection, and IFN-/ synergizes with IFN- to enhance NO production and restrict viral protein synthesis and virus replication

Taken together, these findings suggest that expression of human CD46 in mouse macrophages enhances production of IFN-/ in response to MV infection, and IFN-/ synergizes with IFN- to enhance NO production and restrict viral protein synthesis and virus replication. expressing intact human CD46, viral protein synthesis and development of cytopathic effects were suppressed. Pretreating the added culture medium with antibodies against IFN-/ abrogated these antiviral effects. Taken together, these findings suggest that expression of human CD46 in mouse macrophages enhances production of IFN-/ in response to MV contamination, and IFN-/ synergizes with IFN- to enhance NO production and restrict viral protein synthesis and computer virus replication. This novel function of human CD46 in mouse macrophages requires the CD46 cytoplasmic domains. Measles computer virus (MV) causes a common disease that accounts for about 10% of childhood mortality due to infectious diseases worldwide (5, 29). A Akt2 major pathogenic factor of MV is usually its ability to suppress host cellular CHM 1 immune response, which can lead to severe secondary infections (6, 15). Monocytes and macrophages are major in vivo targets for MV in measles patients (10). These cells serve as a first line defense in the innate immune system against microbial pathogens (12, 26, 27). Interactions between MV and monocytes and macrophages therefore play a pivotal role in measles pathogenesis and host defense against MV. Immature human myelomonocytic cells support MV replication efficiently and produce infectious computer virus (16). By contrast, MV replication in monocytes and differentiated macrophages is usually highly restricted (16, 35, 37). The block in MV replication in those cells appears to be at both posttranscription and posttranslation levels (16). The mechanisms by which monocytes and macrophages suppress MV replication have not been characterized. We recently established a system for studying the interactions between MV and mouse macrophages. Human complement regulatory protein CD46, a receptor for laboratory-adapted MV (9, 30), was expressed in RAW264.7 mouse macrophages. As expected, expression of human CD46 facilitated MV entry into mouse macrophages. Surprisingly, MV protein synthesis and computer virus production were more severely restricted in mouse macrophages expressing human CD46 than in CD46-unfavorable mouse macrophages (20). Subsequently, we showed that mouse macrophages expressing human CD46 produced higher levels of nitric oxide (NO) than CD46-unfavorable mouse macrophages when infected by MV in the presence of gamma interferon (IFN-) (17). Interestingly, deleting the CD46 cytoplasmic domains markedly attenuated NO production in mouse macrophages and rendered these cells highly susceptible to MV contamination (17). NO has potent antimicrobial activities against a wide range of DNA and RNA viruses (32). These results raise the possibility that CD46 can augment antiviral functions in macrophages. To gain further insight into this phenomenon, we examined the IFN-/ response in mouse macrophages expressing human CD46 upon MV contamination, since IFN-/ is usually important for antiviral defense against a wide range of viruses, including MV (22, 36). In this study, we CHM 1 show that mouse macrophages expressing human CD46 produce IFN-/ upon MV contamination. Blocking IFN-/ action by neutralizing antibodies against IFN-/ reverses the inhibition on MV protein synthesis and intensifies viral cytopathic effects (CPE). These antibodies also abrogate the augmenting effect of MV on NO production in mouse macrophages expressing human CD46. Deleting the CD46 cytoplasmic domains greatly attenuates production of IFN-/ from mouse macrophages upon MV contamination but does not prevent these cells from acquiring an antiviral state when treated with culture fluid from MV-infected CHM 1 mouse macrophages bearing intact human CD46. These results provide evidence that human CD46 affects NO production and MV replication in mouse macrophages by modulating production of IFN-/. MATERIALS AND METHODS Cells. RAW264.7 mouse macrophages stably expressing human CD46 with the Cyt1 cytoplasmic domain name or a tailless CD46 mutant were generated as described previously (17, 20). Cells were cultured in RPMI 1640 supplemented with 10% fetal bovine serum (FBS) (GIBCO BRL, Grand Island, N.Y.) and 400 g of the neomycin analogue G418 (GIBCO BRL) per ml. Murine cell line L929 cells (gift from Masae Itoh, Osaka Public Health Institute) were maintained in Eagle’s minimum.