Pulmonary Capillary Confinement Shapes A Motile Anuclear Neutrophil State

The nucleus is a major mechanical constraint for cells moving through confined spaces, but how organ-specific physical environments shape nuclear state and cell behavior in vivo remains unclear. Using quantitative intravital imaging with submicron stabilization of the breathing lung, we tracked neutrophil deformation, Ca²⁺ dynamics, nuclear state and motility over time. In inflamed pulmonary capillaries, neutrophil deformation was temporally coupled to transient Ca²⁺ increases, and this coupling was reduced by the mechanosensitive-channel inhibitor GsMTx4. We identified abundant neutrophil-derived cytoplasts lacking detectable nuclear signal, whose frequency was reduced by GsMTx4 and the peptidylarginine deiminase inhibitor Cl-Amidine. These cytoplasts showed greater morphological plasticity, migration speed and directional persistence than nucleated neutrophils and preferentially associated with Pseudomonas aeruginosa in vivo. Our findings identify the pulmonary capillary bed as an organ-specific mechanical environment that links cell deformation to intracellular signaling, nuclear state and immune-cell behavior.