Abstract
Sera from dogs that were hyporesponsive to interferon (IFN) induction blocked virus induction of IFN in spleen cells in vitro but not IFN action in dog kidney cells. Similarly, macrophages or their culture fluids were found to block IFN induction in lymphoid cells in vitro. Lymphoid cells deprived of phagocytic cells secreted IFN continuously for 4 days, whereas lymphoid cells in the presence of phagocytic cells produced IFN for only 1 day. It was speculated that the 'hyporeactivity factor' in the sera from hyporesponsive dogs was macrophage-derived.