Proteins of this family play an important role in inducing non-specific resistance against a broad range of viral infections. They also affect cell proliferation and modulate immune responses. Produced by peripheral blood leukocytes and lymphoblastoid cells, IFN-α is an acid-stable molecule that signals through IFN-α/βR, which is also used by IFN-β. Both IFNs have similar anti-viral activity and regulate expression of MHC class I antigens. IFN-α contains four highly conserved cysteine residues that form two disulfide bonds, one of which is necessary for biological activity. Recombinant Human IFN-β is a 20.0 kDa protein containing 166 amino acid residues. Due to glycosylation, IFN-β has an approximate MW of 22.3 kDa based on SDS-PAGE gel and Mass Spectrometry.