Even in the absence of infection, the lung is awash in immune cells that play a vital role in protecting the host from airborne pathogens. This image shows some of these cells dispersed throughout a three-dimensional cross-section of a mouse lung.

The adaptive immune system must be finely tuned to mount sufficiently aggressive responses to clear dangerous pathogens, but these responses must not be excessive else they risk causing unnecessary damage to the host. Responses must be particularly well-controlled in the lung, which is both a common entry point for airborne pathogens and an essential organ where damage can be lethal. In this work, we were examining the distribution of immune cells throughout the lung in search of clues to how immune responses are regulated.