Triggering dectin-1-pathway alone is not sufficient to induce cytokine production by murine macrophages

beta-glucans (BG) are abundant polysaccharides of the Saccharomyces cerevisiae cell wall (Sc CW), an industry byproduct. They have immuno-stimulatory properties upon engagement of dectin-1 (Clec7a), their main receptor on particular immune cells, and they actually become of great interest because of their preventive or therapeutic potentials. Zymosan, a crude extract of Sc CW was studied as a prototypic BG, despite its miscellaneous PAMPs content. Here, we examined the response of murine wild type or Clec7a(-/-) bone marrow-derived macrophages (BMDM) to products with increasing BG content (15, 65 or 75%) and compared their effects with those of other dectin-1 ligands. The enrichment process removed TLR ligands while preserving dectin-1 activity. The most enriched extracts have very low NF kappa B activity and triggered low amounts of cytokine production in contrast with crude products like zymosan and BG15. Furthermore, MyD88(-/-) BMDM did not produce TNF alpha in response to crude Sc CW extracts, whereas their response to BG-enriched extracts was unaffected, suggesting that BG alone are not able to initiate cytokine secretion. Although Sc CW-derived BG stimulated the late and strong expression of Csf2 in a dectin-1-dependent manner, they remain poor inducers of chemokine and cytokine production in murine macrophages