Bernardshaw S, Lyberg T, Hetland G, Johnson E. Effect of an extract of the mushroom Agaricus blazei Murill on expression of adhesion molecules and production of reactive oxygen species in monocytes and granulocytes in human whole blood ex vivo. APMIS 2007;115:719–25. We have reported that an extract of the edible officinal mushroom Agaricus blazei Murill (AbM) stimulates synthesis of pro-inflammatory cytokines in human monocytes and vein endothelial cells in vitro and reduces the extent of lethal septicemia in mice with bacterial peritonitis. In the present study on human monocytes and granulocytes in whole blood ex vivo, we studied the dynamic changes of cell adhesion molecules (CD11b, CD62L) and the production of reactive oxygen species (ROS) after stimulation with AbM. The presence of AbM resulted in a similarly increased expression of CD11b in monocytes and granulocytes, although at a lower AbM concentration in monocytes (0.5%) than in granulocytes (2%). Furthermore, there was an AbM-mediated decrease in CD62L expression mirroring the effect on CD11b expression regarding magnitude and dose response. The intracellular production of ROS increased slightly but significantly in granulocytes, but not in monocytes stimulated with AbM. The results suggested that the major effect of AbM on monocytes and granulocytes was the upregulation of CD11b expression, thereby increasing both the phagocytic potential and the ablility to induce diapedesis into inflammatory foci. The rich β-glucan content of AbM could play a crucial role in this immune response.