Interferon-gamma is a potent multifunctional cytokine which is secreted primarily by activated NK cells and T cells. Originally characterized based on anti-viral activities, IFN-gamma also exerts anti-proliferative, immunoregulatory, and proinflammatory activities. IFN-gamma can upregulate MHC class I and II antigen expression by antigen-presenting cells. The 4S.B3 antibody reacts with the human IFN-gamma. The MD-1 antibody reacts with human and monkey interferon-gamma (IFN-gamma). The MD-1 antibody can neutralize the bioactivity of natural or recombinant IFN-gamma.