Microglial enrichment is mechanistically informative only after generalized interferon, stress, cell-cycle, and dissociation components are modeled explicitly. The residual disease-coherent program, not the raw activation score, is the appropriate experimental hypothesis.
Executive interpretation
Activated microglia appear in many neurologic and systemic contexts. A strong enrichment can reflect a disease mechanism, a common interferon response, tissue dissociation, postmortem interval, cell stress, phagocytic activity, or shifts in cell composition. Calling all of these states “disease-associated” creates a biological category that is too broad to test.
Our analysis treats activation as a mixture. We identify the component shared with common technical and inflammatory programs, subtract or condition on that component, and ask whether a residual rare-disease module reproduces across references. The conclusion is deliberately narrower but more actionable: only the reproducible residual should guide perturbation.
Signature architecture
Target modules are constructed from rare-disease genes and phenotype-linked pathways relevant to neuroimmune dysfunction. Control libraries include type I and type II interferon response, immediate-early response, heat shock, oxidative stress, cell cycle, hypoxia, apoptosis, ribosomal shifts, mitochondrial stress, and dissociation-associated programs. Each control is versioned and scored with the same procedure used for the target.
Overlapping genes are not deleted automatically. Shared membership can be biologically meaningful. Instead, we decompose target activity into shared and residual components using regression, matched resampling, and leading-edge inspection. This shows whether the apparent signal is fully explained by a generic response or retains a coherent disease-linked component.
Donor-aware analysis
Microglial states can be represented by thousands of cells from few donors. We aggregate within donor and state, model donor as the independent unit, and avoid testing each cell as a replicate. When covariates are available, age, sex, tissue region, disease status, technical protocol, and postmortem characteristics are retained as design variables or stratification factors.
State abundance and state expression are evaluated separately. More cells in a state can create an apparent program shift even when within-state expression is unchanged. Conversely, expression remodeling can occur without a major abundance change. Conflating the two obscures mechanism.
Cross-dataset comparison
References are compared at the level of broad homeostatic, inflammatory, phagocytic, interferon-responsive, proliferative, and stress-associated neighborhoods, while retaining source-specific labels. Directional meta-analysis is used when the underlying contrast is aligned; otherwise, transfer is assessed through rank and leading-edge concordance.
We require the residual target program to preserve direction across independent datasets and to remain distinguishable from at least one expression-matched control set and the explicit negative-control library. A signal that transfers only in one preprocessing configuration is classified as unstable.
Technical findings
Raw microglial activation scores commonly share substantial structure with interferon, stress, phagolysosomal, and dissociation programs. Removing these components reduces the apparent breadth of the signal. That reduction is not a loss of discovery; it is the removal of explanations that are too general to support the proposed rare-disease mechanism.
The residual programs that remain interpretable are smaller, state bounded, and carried by multiple genes rather than one canonical activation marker. They reproduce as coordinated neighborhoods more reliably than as identical cluster labels. Programs that disappear after control decomposition are reported as nonspecific activation, not as disease mechanisms.
Falsifiable predictions
A disease-coherent residual predicts that perturbing representative module genes in a defined microglial context will alter the residual program more strongly than matched generic stress controls. It also predicts that rescue or correction will reverse the residual without requiring global suppression of interferon or viability programs.
The interpretation would be weakened if the residual is reproduced by unrelated stressors, disappears after donor-aware aggregation, is carried by one dataset, or fails to change under mechanism-matched perturbation.
What the analysis establishes
Raw activation is not specific
Common inflammatory and technical programs explain a meaningful fraction of apparent disease enrichment.
Residualization sharpens the claim
The remaining multi-gene component provides a narrower and more falsifiable hypothesis.
Abundance and expression are different outcomes
Changes in state frequency should not be conflated with within-state transcriptional remodeling.
Donor is the inferential unit
Cell counts increase measurement depth but do not create additional independent biological replicates.
Conclusion and experimental handoff
We conclude that a microglial rare-disease mechanism should be defined as a residual, replicated state program after generic activation and technical signatures have been accounted for. The raw activation label is too nonspecific to nominate a therapeutic direction.
The experimental handoff is a factorial perturbation in microglia with disease-relevant and generic inflammatory stimuli, isogenic genetic perturbation, rescue, and parallel measurements of viability, cytokine response, phagocytic function, and the residual module. This design can distinguish a specific mechanism from generalized immune suppression.
Limitations
- Postmortem and dissociation effects cannot be fully reconstructed from public metadata.
- Microglial states are spatially and temporally dynamic and may not transfer to monoculture.
- Residualization can remove true biology when a disease mechanism genuinely uses a common inflammatory pathway.
- Transcriptomic signatures do not establish protein activity, cell-cell signaling, or causal direction.
Glossary
- Residual program
- The component of a target signature remaining after modeled generic or technical components are accounted for.
- Pseudoreplication
- Incorrect treatment of non-independent observations, such as cells from one donor, as independent replicates.
- State abundance
- The proportion or count of cells assigned to a state within a biological sample.
- Leading-edge inspection
- Review of the genes that carry a signature score to determine whether the same biology reproduces.
Reproducibility and evidentiary scope
This study is a REELD public-data analysis and methods interpretation. It does not report a newly recruited clinical cohort, classify an individual variant, or replace clinical review. A release-ready execution of the workflow includes accession-level provenance, source and ontology versions, code state, environment locks, predefined sensitivity analyses, and output checksums.