Pentraxin 3 is stored in alveolar cell granules. Immunostained images show intracellular presence of Pentraxin 3 (PTX3) inside one cell (red arrow) recovered from the alveolar space of an intubated critically ill patient. In the present study, cells recovered from 20 consecutive bronchoalveolar lavage (BAL) procedures in 20 intubated critically ill patients (see the immunostaining paragraph in the Methods section for details) were stained to measure the fraction of cells remaining after BAL that were positive for intracellular PTX3. The shape of the cell in this picture resembles that of an alveolar leukocyte, which constitutively stores PTX3 inside specific granules. Green represents a fluorescent anti-human PTX3 antibody, and blue are is the cell nucleus stained with bisbenzimide. Yellow arrows indicate nuclei of BAL cells that, apparently, don't store PTX3.