| Popis: |
Alkaline phosphatase (ALPase) activity in neutrophils was examined by enzyme ultracytochemistry at sites of experimentally induced acute inflammation in the rat lung and compared with those in non-inflammatory regions. Neutrophil accumulations in the lung were stimulated by intraperitoneal (IP) injection and intratracheal (IT) instillation of lipopolysaccharide (LPS), an endotoxin from Escherichia coli. Microsliced sections of fixed lung were incubated in a cerium-based reaction medium for the detection of ALPase activity. As cytochemical controls, sections were incubated in a substrate-free medium or in a medium containing 2 mM levamisole for inhibition of ALPase activity. Both IP and IT injections resulted in a significant accumulation of neutrophils in the lung, however, their histological distributions differed, the former stimulating high accumulations within the capillaries and interalveolar spaces, and the latter within the confines of the alveolar spaces. In neutrophils from controls and non-inflamed regions of the lung, ALPase activity was detected as an electron-dense reaction product localized predominantly to small spherical and tubular membrane-bounded cytoplasmic compartments. In the IP-injected rats, prominent ALPase activity was observed at their plasma membrane surfaces, most notably at sites of endothelial cell contact. Following IT instillation of LPS, neutrophils suspended in the alveolar spaces showed a reduced plasma membrane reactivity, however, at type I pneumocyte contact regions, enzyme activity was significantly increased. In all cases, ALPase activity was not detected at the endothelial plasma membranes. Some reaction, however, was seen on the microvilli of the type II surfactant-producing cells. These results indicate that ALPase activity of rat neutrophils in the lung can be increased by LPS injection and that its activity may also be related to the sites of cell-cell interaction and cell surroundings. |
