Distribution and storage of inflammatory memory in barrier tissues

Memories of previous immune events enable barrier tissues to rapidly recall distinct environmental exposures. To effectively inform future responses, these past experiences can be stored in cell types that are long-term residents or essential constituents of tissues. There is an emerging understanding that, in addition to antigen-specific immune cells, diverse haematopoietic, stromal, parenchymal and neuronal cell types can store inflammatory memory. Here, we explore the impact of previous immune activity on various cell lineages with the goal of presenting a unified view of inflammatory memory to environmental exposures (such as allergens, antigens, noxious agents and microorganisms) at barrier tissues. We propose that inflammatory memory is distributed across diverse cell types and stored through shifts in cell states, and we provide a framework to guide future experiments. This distribution and storage may promote adaptation or maladaptation in homeostatic, maintenance and disease settings — especially if the distribution of memory favours cellular cooperation during storage or recall. In this Review, the authors encourage us to extend our concept of memory by considering the diverse cell types within a barrier tissue. They propose that any long-term resident or essential tissue cell type can store memory of previous immune events and cooperate in memory recall.