Brain dysfunction that excessive activation alone cannot fully explain

A review argues that changes in microglia in sepsis-associated encephalopathy (SAE) should be examined as persistent functional reprogramming. Published in Frontiers in Immunology, the paper synthesizes existing knowledge from single-cell multi-omics, which analyzes multiple types of molecular information at the single-cell level, gene-function studies, and in vivo imaging studies to propose a framework for explaining pathological state transitions. It does not report new experimental results or evaluate treatment efficacy in patients.

Microglia are resident immune cells in the brain. They monitor their surroundings, clear cellular debris, and regulate synapses, the connections between neurons. The review describes how these protective functions may become disrupted in SAE, shifting microglia toward states that could cause neural injury. The central question is how systemic inflammation leaves lasting changes in the function of brain immune cells. The authors argue that activation level alone cannot adequately explain imbalances in surveillance and clearance or differences in recovery processes.

A framework that considers reduced surveillance alongside excessive synapse removal

The authors’ concept of reprogramming goes beyond changes in gene expression. It links the reception of inflammatory signals, epigenetic changes that regulate gene activity without altering the DNA sequence, the reorganization of energy metabolism, and resulting functional abnormalities. The approach also considers the possibility that functional changes may persist even after the expression of some genes recovers. However, not all of these links have been established in human SAE.

The functional abnormalities reviewed include reduced environmental surveillance, excessive synapse removal, and imbalances in clearance capacity depending on the target. In particular, preclinical studies related to SAE have examined microglial removal of synapses marked by complement proteins of the immune system. This offers a clue for investigating pathways from inflammation to neural circuit damage, but it cannot be assumed to be a mechanism that applies uniformly across patients.

Timing and location also matter. The review explains that microglial states differ between acute inflammation and recovery, and that responses vary across brain regions. A reduction in inflammatory signals alone may therefore be insufficient to determine whether normal surveillance and synaptic regulation have recovered. The authors propose studying both the process of state transition and the possibility of reversing it.

Evidence for treatment strategies and limits to clinical translation

The therapeutic directions reviewed include modulation of epigenetic and metabolic pathways, gene regulation, and cell replacement; the strength of evidence varies by strategy. CRISPR-based functional investigation is presented as a tool for identifying microglial regulatory genes and targets. The use of engineered cells to selectively control pathological signals is a conceptual proposal in SAE. Because the review also includes findings from studies of other neurological diseases, readers should distinguish whether each strategy has direct evidence in SAE.

A substantial gap remains before clinical translation. According to the review, much of the mechanistic and therapeutic research relies on young, healthy rodents, whereas many patients with SAE are older or have comorbidities. The blood–brain barrier, which restricts movement of substances between blood and brain tissue, also poses an obstacle to the delivery of drugs, gene-regulation tools, and cells. An intervention that is beneficial during the acute phase may be ineffective or harmful later, so treatment timing requires separate validation.

There is no basis for interpreting the directions proposed in this review as evidence of improved cognitive recovery or survival in patients. Further work must validate the proposed mechanisms and treatment strategies while accounting for interactions among microglia, neurons, other immune cells, and the blood–brain barrier. The original review is available in Frontiers in Immunology.