β-Glucans: Old Molecules with Newly Discovered Immunological Activities

β-glucans (BG) are polysaccharides contained in the cell wall of fungi but also present in nature as normal constituents of oats, barley and yeast. The recent discovery of the major receptor for BG on antigen-presenting cells, dectin-1, has given a strong impetus to a series of researches on BG immunobiological activities. In particular, BG possess antimicrobial activity by exerting a direct effect on monocytes and neutrophils. At the same time, BG-induced removal of inflammatory cells from infectious foci and suppression of proinflammatory cytokines support the antiinflammatory ability of this molecule. BG have been detected in serum of patients with fungal infections and hepatitis C virus infection by means of the Limulus amebocyte lysate assay. Data suggest the antiinflammatory role of BG in these patients, even if the exact nature of circulating BG is still unknown. Of note, clinical trials in patients with postsurgical infections, sepsis and trauma have been conducted by administration of BG in alternative to corticosteroid and anti-cytokine monoclonal antibody (MoAb) therapy which give rise to more serious side effects. As far as anticancer activity of BG is concerned, evidence has been provided that BG behave as an adjuvant for MoAb therapy against tumors. In fact, in a murine model, it was demonstrated that granulocytes with BG bound to CR3 could kill iC3b coated tumor cells, thus potentiating the tumoricidal activity of MoAbs. Taken together, these studies seem to support a beneficial role of BG in the host, even if the exact mechanisms of action of this molecule on the immune network deserves furter elucidation.