The immune system is constantly performing surveillance to detect foreign organisms that might do harm. But pathogens, for their part, have evolved a number of strategies to evade this detection, such as secreting proteins that hinder a host's ability to mount an immune response. In a new study, a team of researchers led by Dr. Igor E. Brodsky of the University of Pennsylvania, identified a "back-up alarm" system in host cells that responds to a pathogen's attempt to subvert the immune system. "In the context of an infection, the cells that are dying are talking to the other cells that aren't infected," said Dr. Brodsky, an Assistant Professor in the Department of Pathobiology in Penn's School of Veterinary Medicine and senior author on the study. "I don't think of it as altruistic, exactly, but it's a way for the cells that can't respond any longer to still alert their neighbors that a pathogen is present." The findings address the long-standing question of how a host can generate an immune response to something that is designed to shut off that very response. A potential future application of this new understanding may enable the cell-death pathway triggered by bacteria to be harnessed in order to target tumor cells and encourage their demise. The work was published online on August 30, 2017 in the Journal of Experimental Medicine. The article is titled “RIPK1-Dependent Apoptosis Bypasses Pathogen Blockade of Innate Signaling to Promote Immune Defense.” A major way that the immune system recognizes pathogens is by detecting patterns that are shared among microbes but are distinct from a host's own cells. Pathogens, however, don't make it easy for immune cells to destroy them. Some can inject proteins into host cells that interfere with this detection, allowing an infection to become established.
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