Abstract
CD 46, a complement regulatory protein widely expressed on human cells, serves as an entry receptor for measles virus (MV). We have previously shown that the expression of human CD 46 in mouse macrophages restricts MV replication in these cells and enhances the production of nitric oxide (NO) in the presence of gamma interferon (IFN-γ). In this study, we show that crosslinking human CD 46 expressed on the mouse macrophage-like cell line RAW 264.7 with purified C3b multimer but not monomer enhances NO production. The enhanced production of NO in response to IFN-γ was observed again with C3b multimer but not monomer. The augmentation of NO production is human CD46-dependent with a CYT1>CYT2 profile. Thus, the reported MV-mediated NO production, irrespective of whether it is IFN-γ-dependent or -independent, should be largely attributable to CD 46 signaling but not to MV replication. Similar CYT1-dependent augmentation of NO production was reproducible with two CD 46 ligating reagents, CD46-specific monoclonal antibodies (mAb) or their F(ab')2 and MV hemagglutinin (H) and fusion (F) glycoproteins. Co-cultivation of mouse macrophages bearing human CD 46 with Chinese hamster ovary (CHO) cells expressing MV H and F enhanced 1FN-γ-induced NO production. Yet, the NO levels induced by F(ab')2 against CD 46 or MV H/F on CHO cells were much lower than those induced by CD46-crosslinking mAb with Fc or MV infection. Removing the cytoplasmic tails of CD 46 abrogated the augmentation of NO production triggered by all three stimulators. Thus, the CD 46 CYT 1 and CYT 2 isoforms functionally diverge to elicit innate immune responses, which can be modulated by purified C3b multimer or anti-CD 46 mAbs.
