Potentiation of histamine release by microfungal (1→3)- and (1→6)-β-D-Glucans

(1 -> 3)-beta-D-Glucans, a cell wall component in most microfungi, are suggested to play a role in the development of respiratory and general symptoms in organic dust-related diseases. The mechanisms by which they induce these effects are, however, not clear. In the present study, mediator release and its potentiation by the (1 -> 3)-beta-D-glucan as well as by the (1 -> 6)-beta-D-glucan found in yeast and other fungi were therefore examined. Blood leucocytes from healthy volunteers and from patients allergic to house dust mite were incubated with (1 -> 3)-beta-D-glucans with increasing 1,6-branchings: curdlan [a linear (1 -> 3)-beta-D-glucan], laminarin and scleroglucan, and furthermore with pustulan, a linear (1 -> 6)-beta-D-glucan. Histamine release was not observed on exposure to the glucans only, but in the presence of anti-immunoglobulin E (IgE) antibody or specific antigens, all the glucans investigated led to an enhancement of the IgE-mediated histamine release. The glucans induced a significant potentiation of the mediator release when present at concentrations in the range of 2-5 x 10(-5) M. These results suggest that (1 -> 3)-beta-D-glucan as well as (1 -> 6)-beta-D-glucan aggravates IgE-mediated histamine release. Knowledge concerning the effects of glucans on immune responses may be of importance for understanding and treating inflammatory and allergic diseases.