Decreased sialidase activity in alveolar macrophages of guinea pigs exposed to coal mine dust.

Abstract

The origin of immune dysfunctions that are observed in pneumoconiotic miners still remains unknown. There is evidence that th carbohydrate mdety ofmembrane glycoconjugates is ofprimar importance in many fuctions ofunmunocompe tent cells. The glycosylation, and especiafly the sialylation level of membrane components of various lymphocyte and macrophage subsets, vary depending on the state of ceUlular differentiation and activation. Siises, which may regulate the amount ofsialic acids exposed on the cell membrane, can thus be considered as immunoregulatory enzymes. In this report, the sialidase activity has been measured in alveolar macrophages (AM) and in cell-free bronchoalveolar lavage fluid (BALF) from guinea pigsexposed for 4 months to coal mine dust at a concentration of300 mg/m3. The samples were collected by bronchoalveolar lavage 2 months after cessation ofexposure. The sialidase activity in the cell-free fluid and in the purified alveolar macrophages showed a 10-fold decrease (p< .OO1). Kinetic parameters ofthe enzyme such as K.and optimum pH did not change. This changed activity was specific for sialidase, as two other lysosomal glycosidases, ,-galactosidase and N-acetylglucosaminidase, showed unchanged activities. These results suggest the possibility that, by inducing a decreased sialidase activity, exposure to coal mine dust may lead to a modified expression of AM membraneasciated sialic acids giving rise to altered immune functions (i. e., phagocytosis, antigen processing, response toctokines, etc.).