A group of Berkeley Lab and UC Berkeley physical chemists led by Jay Groves, faculty scientist in Molecular Biophysics and Integrated Bioimaging (MBIB), has—for the first time—imaged the process by which an individual immune system molecule is switched on in response to a signal from the environment. This breakthrough led to the discovery that the immune system activation process involves hundreds of proteins suddenly coming together to form a linked network through a process known as phase transition. Critically, the process has a built in time delay which allows the cell to distinguish a genuine receptor stimulation from background chemical noise. The work is described in a paper recently published in the journal Science.