(1->3)-β-D-glucan derivatives with unique structural properties differentially affect murine lung inflammation and histology.

Background{beta}-D-glucan (BDG) compounds are proinflammatory fungal cell wall polysaccharides known to cause respiratory pathology. However, the specific immunological effect of unique BDG structures on pulmonary inflammation is understudied. We sought to characterize the effect of four unique fungal BDGs with unique branching patterns, solubility, molecular weights and higher order structure in murine airways. MethodsScleroglucan (1[->]3) (1[->]6)-highly branched BDG, laminarin (1[->]3) (1[->]6)-branched BDG, curdlan (1[->]3)-linear BDG, and pustulan (1[->]6)-linear BDG were assessed by nuclear magnetic resonance spectroscopy (NMR). Glucan compounds were confirmed negative for endotoxin by kinetic chromogenic Limulus amebocyte lysate assay. Each BDG was tested using an inhalation model with C3HeB/FeJ mice and compared to control mice exposed to saline and unexposed sentinels (all, n=3-19). Inhalation studies were performed using all BDGs {+/-}heat-inactivation (1-hr. autoclave) given BDG solubility increases after heat-inactivation. Outcomes included bronchoalveolar lavage (BAL), differential cell counts (macrophages, neutrophils, lymphocytes, and eosinophils), BALF cytokine and serum IgE and IgG2a expression (by multiplex immunoassay and ELISA). Lastly, ex vivo cultured left lung cells were BDG stimulated, and cytokines (multiplex) compared to unstimulated cells. Right lung histology was performed. ResultsWhile each BDG affected lung inflammatory outcomes, pustulan exposure led to the most pro-inflammatory profile of all BDGs tested, including increased inflammatory infiltrate into BAL, increased serum IgE and IgG2a and increased cytokine production. Secondary stimulation of sensitized lung cells by lipopolysaccharide (LPS) significantly increased cytokine expression. Lung histology revealed significant fibrosis in lungs exposed to soluble BDGs pustulan and scleroglucan. ConclusionInhalation of BDGs with distinct branching patterns exhibited varying inflammatory potency and immunogenicity, which lichen-derived pustulan having the greatest effect. Glucan source and solubility should be considered in exposure and toxicological studies.