[Morphology of mast cells in experimental pulmonary fibrosis induced with bleomysin]

Bleomycin induces local inflammatory process with subsequent pulmonary fibrosis. An unknown chemoattractant induces the mast cell (MC) migration to the injured lung tissue. Aim of this study was evaluation of the number, topography and ultrastructure (TEM) of the MC in rat lungs with bleomycin-induced fibrosis. The bleomycin was administered once intratracheally (3.6 mg/kg). The animals were sacrificed on 7th. 14th and 21st day of experiment. MC were stained with Csaba's method. An evident increase in MC number related to the phase of experiment and stage of lung fibrosis was observed: 520, 1200, 4745 per cm2 section on the 7th, 14th and 21st day respectively. In control the MC number was 163 per cm2 section (p < 0.001). On the 7th day the MC were rich in red granules (mature granules with preponderance of heparin). They were located mainly in pleura and around the blood vessels, as in control. On the 14th and 21st day the majority of MC was situated in places of active fibrosing. They contained exclusively blue granules (the young granules with preponderance of biogenic amines), mixture of increased secretory function of the MC in the fibrotic lungs. Some of the MC granules showed fusion and altered matrix contents, other were emptied in piecemeal manner. A net of microtubules connected the granules was observed. Degranulation of MC may release heparin and cytokines able to stimulate synthesis of extracellular matrix. It has been suggested that heparin contributes to the fibrotic process and angiogenesis, stimulating directly or indirectly collagen synthesis by binding, stabilization and activation of fibroblast growth factor (FGF) and cell adhesion glycoproteins.