Most mammalian species have multiple IFN-a subtypes. Although the reasons for these multiple subtypes are not fully known, there are clear cell type and temporal differences in their expression. A recent study established a nomenclature for the murine IFN-a subtypes (van Pesch et al. 2004) and determined relative activities of the subtypes with protein quantification by phosphorimaging of metabolically-labeled protein. In this study, Mu IFN-a4 was deemed to have average antiviral activity when compared with the potency of the other subtypes. Mu IFN-a4 was initially cloned by Zwarthoff et al. [(1985) Nuc. Acids Res. 13(3) 791], and has been extensively studied. It is apparently expressed early in viral infection in a protein synthesis independent manner, and its expression is induced by phosphorylation of IRF-3. It may be that Mu IFN-a4, like IFN-b, has a priming function on cells, enabling the expression of other Mu IFN-a subtypes [Reviewed by Mesplede et al. (2003) Autoimmunity 36(8):447 and Asselin-Paturel & Trinchieri (2005) J. Exp. Med. 202(4):461]. Thus, this interferon is among the first observed after viral infection. Intriguingly, while this interferon is expressed in a large variety of cell types, one report suggests that the expression level in dendritic cells is low to non-existent [Barchet et al. (2002) J. Exp. Med. 195(4):507] Source: Recombinant corresponding to murine (C57/Bl) DNA expressed in mammalian cells. Molecular Weight: ~19.5kD Biological Activity: Determined relative to a lab standard of Mu IFN-alpha A which was calibrated to the NIH Murine IFN-a standard (Ga02-901-511). Mouse (L929/EMCV) in this assay the EC50 for IFN is ~5U/ml. Endotoxin: ~1EU/ug Activity (units/ml): As Reported Specific Activity (units/mg): As Reported Storage and Stability: Aliquot to avoid repeated freezing and thawing and store at -70C. Aliquots are stable for 6 months. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.
