SECRETION OF TNF-ALPHA BY ALVEOLAR MACROPHAGES IN RESPONSE TO CANDIDA-ALBICANS MANNAN

Resident alveolar macrophages (AM phi) were tested for their ability to respond to Candida albicans mannan. AM phi were found to produce tumor necrosis factor alpha (TNF-alpha) in vitro in response to mannan stimulation. TNF-alpha secretion was measured using ELISA and L929B cellular cytotoxicity assays. Cytotoxicity was neutralized in parallel L929B cell cultures by the addition of rabbit anti-TNF-alpha antibody. Mannan preparations were found to be free of contaminating LPS by Limulus assay. When AM phi were cultivated for 18 h at 37 degrees C, 67 mu g of mannan stimulated the secretion of approximately 207 U/ml of TNF-alpha. By comparison, AM phi treated with 6.7 mu g of LPS secreted approximately 257 U/ml of TNF-alpha. Optimal TNF-alpha production occurred between 9 and 18 h after mannan stimulation. Disparate mechanisms for stimulation of TNF-alpha secretion were suggested by differential sugar blockade of LPS- and mannan-induced TNF-alpha secretion. The addition of 2% D-mannose or 2% alpha-methyl-D-mannoside to AM phi cultures blocked mannan- but not LPS-stimulated TNF-alpha secretion. Furthermore, the addition of rabbit anti-mannan antibody to mannan-coated plastic culture dishes prevented TNF-alpha secretion by the mannan-sensitive RAW 264.7 cell line. Moreover, the data suggest that C. albicans mannan stimulated AM phi to secrete TNF-alpha by an LPS-independent receptor mechanism which may also function as a mannose receptor.