Comparison of the potency of a variety of β-glucans to induce cytokine production in human whole blood

Abstract

β-Glucans are components of fungal cell walls and potent stimulants of innate immunity. The majority of research on biological activities of glucans has focused on β-(1→3)-glucans, which have been implicated in relation to fungal exposure-associated respiratory symptoms and as important stimulatory agents in anti-fungal immune responses. Fungi-and bacteria and plants-produce a wide variety of glucans with vast differences in the proportion and arrangement of their β-(1→3)-, -(1→4)- and -(1→6)-glycosidic linkages. Thus far, the pro-inflammatory potential of different β-glucans has not been studied within the same experimental model. Therefore, we compared the potency of 13 different glucan preparations to induce in vitro production of IL-1β, IL-6, IL-8 and TNF-α in human, whole blood cultures. The strongest inducers of all cytokines were pustulan [β-(1→6)-glucan], lichenan [β-(1→3)-(1→4)-glucan], xyloglucan [β-(1→4)-glucan] and pullulan [α-(1→4)-(1→6)-glucan]. Moderate-to-strong cytokine production was observed for curdlan [β-(1→3)-glucan], baker's yeast glucan [β-(1→3)-(1→6)-glucan] and barley glucan [β-(1→3)-(1→4)-glucan], while all other glucan preparations induced very low, or no, detectable levels of cytokines. We therefore conclude that innate immunity reactions are not exclusively induced by β-(1→3)-glucans, but also by β-(1→6)- and β-(1→4)-structures. Thus, not only β-(1→3)-glucan, but also other β-glucans and particularly β-(1→6)-glucans should be considered in future research.

Figure 1. Comparison between IL 6 concentrations in whole blood of three donors after stimulation with 250μg/ml glucan

A: donor 1 (x-axis) vs donor 2 (y-axis); B: donor 1 (x-axis) vs donor 3 (y-axis); C: donor 2 (x-axis) vs donor 3 (y-axis). BAK: baker’s yeast glucan; BAR: barley β-glucan; CUR: curdlan; LAM: laminarin; LIC: lichenan; oat: oat β-glucan; PAC: pachyman; PAR: paramylon; PUL: pullulan; PUS: pustulan; SCH: schizophyllan; SCL: scleroglucan; XYL: xyloglucan

Figure 2

Median cytokine levels in whole blood of three donors after 24h stimulation with LPS and various glucan preparations. The different panels represent in vertical direction the measured median levels of IL6, IL1β, IL8 and TNFα and in horizontal direction the results for LPS (A) and glucans derived from fungi (B), lichen (C), algae and bacteria (D) and plants (E);

Figure 3. Comparison of productions of different cytokines in response to the various glucans

A: IL 1β vs. IL 6; B: IL 1β vs. IL 8; C: IL 1β vs. TNF α; D: IL 6 vs IL8; E: IL 6 vs. TNF α; F: IL 8 vs. TNF α; Abbreviations as in figure 1.

Figure 4

Comparison of IL6 concentrations induced in the WBA by six glucans (baker’s yeast glucan, pullulan, pustulan, lichenan, curdlan, xyloglucan) and the LPS positive control solution before (closed symbols) and after polymyxin treatment (open symbols).