Unraveling the Complexity: Biofilms and Their Interactions with Myeloid Immune Cells

In higher organisms, the immune system enables the host to effectively combat the invasion and dissemination of microbial pathogens. Nonetheless, microbes have evolved multifaceted strategies to overcome the protective barriers posed by the host. Many bacteria avoid immune recognition by forming aggregates in a matrix of extracellular polymeric substances that limit the infiltration of host immune cells and subsequent immune activation. The transition from solitary planktonic existence to structured biofilms results in significant alterations in the myeloid cell compartments, not just within the infected tissue but also in the broader systemic immune landscape outside the biofilm microenvironment. Indeed, emerging evidence suggests that biofilm progressively induces local and systemic immune tolerance through various mechanisms that facilitate immune cell death, accumulate immunosuppressive cells, or produce effector molecules that inactivate host defenses. In this chapter, we summarize the current knowledge exploring the range of strategies used by bacterial biofilms to avert the activation and differentiation of myeloid cells. We also discuss the evolving understanding of how bacterial biofilms shape heterogeneity and the functional landscape of myeloid cells.