Fibroblasts are in a position to provide directional information to migrating neutrophils during pneumonia in rabbit lungs

Previous findings have shown that pulmonary fibroblasts are associated with preexisting holes in the endothelial and epithelial basal laminae through which neutrophils appear to enter and leave the interstitium as they migrate from capillaries to alveoli. To determine their role in neutrophil migration, fibroblast organization within the interstitium was assessed by transmission electron microscope observations of serial-sectioned rabbit lung tissue. Interstitial fibroblasts were found to physically interconnect the endothelial basal lamina holes to epithelial basal lamina holes. Morphometric assessment of rabbit lung tissue instilled with Streptococcus pneumoniae revealed that approximately 70% of the surface area density of migrating neutrophils is in close contact (15 nm or less) with interstitial fibroblasts and extracellular matrix elements (30 and 40%, respectively). Although migrating neutrophils were close enough to adhere to both fibroblasts and extracellular elements, the interstitial fibroblasts are organized in a manner that would allow them to provide directional information to the neutrophils. A model illustrating this process is proposed.