The form of (1-3)-beta-D
glucan found in the cell walls of the anamorphic Trichocomaceae that grow on damp building materials is considered to have potent toxic and inflammatory effects on cells of the respiratory system. It is also considered to have a potential role in the development of non-allergenic respiratory health effects. While human studies involving experimental exposures all point to the inflammatory potential of pure
curdlan, a linear (1-3)-beta-D
glucan in a triple helix configuration, animal experiments result in conflicting conclusions concerning the inflammatory potency of this
glucan. However, because mice appear to be a better model than guinea pigs for exploring the respiratory effects of
curdlan and because molecular mechanisms associated with this
glucan remain largely unknown, we conducted further work to clarify the role of
curdlan on the inflammatory response using our mouse model of
lung disease. This study used in situ hybridization (ISH) to probe
dectin-1 mRNA transcription with a
digoxigenin-labeled
cDNA probe, with reverse transcription (RT)-PCR based arrays used to measure
inflammation gene and receptor transcriptional responses. Also, immunohistochemistry (IHC) was used to probe
dectin-1 as well as anti-mouse Ccl3, Il1-alpha, and
TNF-alpha expression to evaluate dose and time-course (4 and 12 h) postexposure (PE) response patterns in the lungs of intratracheally instilled mice exposed to a single 50 mul dose of
curdlan at 10(-7), 10(-8), 10(-9), and 10(-10) M/animal (=4 mug to 4 ng
curdlan/kg lung wt).
Dectin-1 mRNA transcription and expression was observed in bronchiolar epithelium, alveolar macrophages (AMs), and alveolar type II cells (ATIIs) of lungs exposed to 4 mug to 40 ng
curdlan/kg lung wt, at both time points. Compared to controls, array analysis revealed that 54 of 83 genes assayed were significantly modulated by
curdlan.
mRNA transcription patterns showed both dose and time dependency, with highest transcription levels in 10(-7) and 10(-8) M treatment animals, especially at 4-h PE. Nine gene
mRNA transcripts (Ccl3, Ccl11, Ccl17, Ifng, Il1alpha, Il-20,
TNF-alpha, Tnfrsf1b, and CD40lg) were significantly expressed at all doses suggesting they may have a central role in immunomodulating
curdlan exposures. IHC revealed Ccl3, Il1-alpha, and
TNF-alpha expression in bronchiolar epithelium, AMs and ATIIs illustrate the important immunomodulatory role that these cells have in the recognition of, and response to
glucan. Collectively, these results confirm the inflammatory nature of
curdlan and demonstrate the complex of
inflammation-associated gene responses induced by (1-3)-beta-D
glucan in triple helical forms. These observations also provide a
biological basis for the
irritant and inflammatory response to
curdlan observed in humans and animals in experimental studies.