Monocyte exposure to Saccharomyces cerevisiae cell wall mannan and decreased TNF-alpha production in mild asthma: a role for mannan-binding lectin?

A correlation between fungal exposure and aggravation of inflammatory symptoms in asthmatic individuals is well documented in the literature. However, the molecular mediators responsible for clinical symptoms due to fungal exposure in individuals with asthma are still not known. The fungal cell wall polysaccharide mannan stimulates production of pro-inflammatory cytokines such as tumour necrosis factor (TNF)-alpha in monocytes. Recently, a role for the plasma protein mannan-binding lectin (MBL) has been proposed in individuals with severe asthmatic disease, although little is known about its role in those with mild and untreated asthma. MBL has been reported to modulate inflammatory cytokine production, but the mechanisms are not known. We conducted a pilot study and found that the cell wall mannan preparation used stimulated lower TNF-alpha production by monocytes from asthmatic subjects compared with that from healthy subjects in the presence of autologous plasma. Lipopolysaccharide-induced TNF-alpha production was not significantly different between the groups. Further, plasma MBL levels in individuals with mild asthma were slightly increased compared with those in normal subjects, although the difference was not statistically significant. We speculate that reduced TNF-alpha production in monocytes from asthmatic subjects after fungal cell wall mannan stimulation could partly be influenced by plasma components such as MBL.