β-glucan-induced innate immune memory distinctively affects macrophage activation in response to differential environmental cues

Abstract

In vitro, exposure of human primary monocytes to the fungal {beta}-glucan enhances their pro-inflammatory responsiveness towards several pathogens. Yet, the role of environmental condition of this process remains unclear. Here we found that {beta}-glucan-induced innate immune memory counteract the anti-inflammatory status of the macrophages. In response to {beta}-glucan imprinting, M-CSF-(M2-like-) macrophages increase their pro-inflammatory responsiveness to secondary stimuli associated with decrease of the M-CSF differentiation hallmarks. In contrast, in GM-CSF-(M1-like-) environment, {beta}-glucan imprinting reduced the pro-inflammatory canonical feature of the macrophages, together with their terminal differentiation marks. Comparing M-CSF and GM-CSF environment, we observed that {beta}-glucan-imprinted macrophages present comparable functions in terms of cytokine responses, phagocytosis, oxidative burst, and angiogenesis. This effect is mediated through Dectin-1 and associated with altered expression of the master regulators of macrophage terminal differentiation, IRF5 and IRF3. {beta}-glucan-induced innate immune memory skews the commitment of the macrophages in complex environment towards similar and less terminally differentiated cells. Together, these observations suggest a potential therapeutic role for {beta}-glucan-induced modulation of innate memory in different pathological contexts.