🧬 biology

Age but not sex modifies lymphoid immune responses in murine sepsis

This study utilizes single-cell RNA sequencing to demonstrate that while both age and sex shape baseline lymphoid composition in murine sepsis, aging uniquely drives distinct transcriptional reprogramming, metabolic shifts, and altered drug response profiles in lymphocytes, whereas sex does not significantly modify the septic immune response.

Original authors: Dayuan Wang, Christine Rodhouse, Hongru Tang, Miguel Hernández-Ríos, Xuanxuan Yu, Ruoxuan Wu, Whitman Wiggins, Marvin L. Dirain, Ricardo Ungaro, Dina C. Nacionales, Lyle L. Moldawer, Shawn Larson, Mic

Published 2026-06-25

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Dayuan Wang, Christine Rodhouse, Hongru Tang, Miguel Hernández-Ríos, Xuanxuan Yu, Ruoxuan Wu, Whitman Wiggins, Marvin L. Dirain, Ricardo Ungaro, Dina C. Nacionales, Lyle L. Moldawer, Shawn Larson, Michael Kladde, Clayton Mathews, Paramita Chakrabarty, Gemma Casadesus, Jaimar C. Rincon, Larissa Langhi Prata, Feifei Xiao, Maigan A. Brusko, Robert Maile, Philip A. Efron, Guoshuai Cai

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

The Big Picture: A Tale of Two Defenses

Imagine your body's immune system as a highly trained security team guarding a castle (your body). When a burglar breaks in (an infection like sepsis), the team springs into action.

This study looked at what happens to this security team when the castle is attacked, comparing young guards to older guards. The researchers also checked if being male or female made a difference in how the team reacted.

They used a high-tech microscope (single-cell RNA sequencing) to look at the "instruction manuals" inside individual immune cells in the spleen (a major immune organ) of mice.

The Main Discovery: Age is the Boss, Sex is a Sidekick

The most surprising finding was that age completely changed how the immune team reacted to the attack, but sex (male vs. female) barely mattered at all.

The Analogy: Think of the immune system as a car.
- Age is like the engine's wear and tear. A brand-new car (young mouse) and a 20-year-old car (old mouse) drive very differently when you slam on the brakes (sepsis). The old car's engine sputters, the brakes squeal, and the whole system reacts in a chaotic, exaggerated way.
- Sex is like the color of the car paint. Whether the car is red or blue, the engine and brakes work the same way. In this study, the "paint color" didn't change how the car handled the emergency.

What Happened to the "Security Team"?

1. The Numbers Game (Who is missing?)
When the infection hit, both young and old mice lost a lot of their immune cells (like guards running out of the castle).

Young Mice: Lost a standard amount of T-cells and NK cells (the "fighters").
Older Mice: Started with fewer fighters to begin with. When the infection hit, they lost even fewer fighters, but they lost a huge number of B-cells (the "architects" who design weapons).
The Twist: In older mice, the B-cells didn't just disappear; they rushed to turn into Plasma Cells (the "weapon factories"). The older mice's immune system tried to compensate for the loss by frantically mass-producing weapons, but this reaction was messy and unbalanced.

2. The Instruction Manuals (Gene Activity)
The researchers looked at the "to-do lists" inside the cells.

The "Old" Baseline: Before the infection, the older mice's immune cells were already tired. Their "metabolic" (energy) to-do lists were crossed out (low energy), but their "immune alarm" lists were already written in red (high alert).
The Sepsis Shock: When the infection hit, the young mice's cells flipped their lists normally. But the older mice's cells went into overdrive. Because they were already "tired" and "on high alert," the infection caused them to flip their lists into a state of chaotic exaggeration.
- Analogy: Imagine a tired runner (older mouse) who is already jogging in place. When you tell them to sprint (sepsis), they don't just run faster; they sprint so hard they trip and fall. Their energy systems get overwhelmed because they started from a place of exhaustion.

3. The Communication Breakdown
Immune cells need to talk to each other to coordinate.

The Signal: The "generals" (Antigen-Presenting Cells) need to send signals to the "soldiers" (T-cells) to tell them where to fight.
The Result: In young mice, the infection made the generals stop talking to the soldiers (a normal shutdown to prevent overreaction). In older mice, the generals kept talking or even talked more to the soldiers.
Why it matters: This constant, loud shouting in an already exhausted system likely confuses the soldiers and makes the immune response less effective, rather than stronger.

4. The "Drug Map"
Finally, the researchers looked at which medicines might work on these cells.

They found that the "locks" on the cells (drug targets) looked very different in older mice compared to younger ones after the infection.
Analogy: If you are trying to open a door with a key, the lock on the young mouse's door is standard. The lock on the older mouse's door has been twisted and warped by age and infection. A key that fits the young mouse perfectly might not fit the older mouse at all. This suggests that a "one-size-fits-all" medicine won't work; older patients might need a completely different "key" (drug).

Summary of the Findings

Age matters: Aging changes the immune system's baseline (it starts tired and confused) and makes it react to infection in a wild, unbalanced way.
Sex doesn't matter (in this context): Being male or female didn't significantly change how the lymphoid immune cells reacted to the infection.
The B-Cell Shift: Older mice had a unique reaction where their B-cells rushed to become weapon factories, but this happened in a disorganized way.
The Takeaway: The immune system in older adults isn't just "weaker"; it's dysregulated. It starts from a broken baseline and reacts to stress with chaos. This explains why older people often have worse outcomes with sepsis and why they might need different treatments than younger people.

What the study did NOT say:

It did not test specific drugs on humans.
It did not claim that sex is irrelevant to immunity in general, only that it wasn't a major factor in this specific part of the immune system during this specific type of infection in mice.
It did not provide a cure, but rather a detailed map of why the problem happens.

Technical Summary: Age but not sex modifies lymphoid immune responses in murine sepsis

Problem Statement
Sepsis remains a devastating condition with high incidence and poor long-term outcomes, particularly among the elderly. Despite decades of research, effective immunomodulators to improve patient survival have been elusive. A central driver of poor prognosis is the profound dysregulation of lymphocytes, a phenomenon exacerbated by chronological aging (immunosenescence). While it is established that both age and sex influence immune responses, the specific mechanisms by which these host factors differentially remodel the lymphoid transcriptional landscape during sepsis are poorly defined. Previous research has largely focused on CD4+ T cells, leaving other lymphocyte subsets and their interactions with antigen-presenting cells (APCs) understudied in the context of age and sex. Furthermore, the "one-size-fits-all" therapeutic approach has failed to account for how fundamental biological differences, such as age, might necessitate distinct therapeutic strategies.

Methodology
The authors employed a comprehensive single-cell RNA sequencing (scRNA-seq) approach to map the splenic lymphoid landscape in a murine model of sepsis that better recapitulates the human condition than historical models.

Experimental Design: The study utilized C57BL/6J mice stratified by age (young adult: 3–4 months; older adult: 18–24 months) and sex (male and female). Sepsis was induced via cecal ligation and puncture combined with daily chronic stress for seven days (CLP + DCS 7d). A total of 57 mice (28 naive, 29 septic) were analyzed.
Data Generation: Splenocytes were harvested from surviving animals at day 7. Single-cell libraries were prepared using the 10X Genomics Chromium Next GEM Single Cell 5' v2 kit and sequenced on the Illumina Novaseq X plus platform, yielding a high-quality dataset of 828,744 cells.
Bioinformatics and Statistical Analysis:
- Processing: Data were processed using Cell Ranger and Seurat, with batch correction performed via Harmony. Cell identities were assigned based on canonical marker genes.
- Statistical Modeling: A unified linear model ( $Y \sim \beta_0 + \beta_1\text{age} + \beta_2\text{sex} + \beta_3\text{sepsis} + \beta_4(\text{age} \times \text{sepsis}) + \beta_5(\text{sex} \times \text{sepsis})$ ) was applied to assess main effects and interaction effects on cell proportions, gene expression, intercellular communication, RNA velocity, and drug-target potential.
- Specific Analyses: Differential expression was performed on pseudobulk profiles using DESeq2. Gene set enrichment analysis (GSEA) utilized the GO Biological Process database. Intercellular communication was inferred using CellChat. RNA velocity was calculated via scVelo to map differentiation trajectories. Drug-target landscapes were mapped using Drug2cell.

Key Results

Cellular Composition: Sepsis induced a global reduction in lymphocyte proportions (B, CD4+ T, CD8+ T, NK cells) and an expansion of plasma cells across all groups. However, age significantly modified these responses, whereas sex had minimal impact. Older adult mice exhibited a distinct baseline characterized by reduced T and NK cell proportions and an expanded B cell compartment. Post-sepsis, older mice showed a less pronounced depletion of T/NK cells but a significantly enhanced shift from B cells to plasma cells compared to young mice.
Transcriptional Remodeling: Aging and sepsis drove extensive transcriptional changes, but sex did not. A striking reciprocal relationship was observed between aging and sepsis effects, particularly in B cells: genes upregulated by sepsis were largely downregulated at the aged baseline, and vice versa. This suggests that aging establishes a dysregulated baseline that leads to exaggerated transcriptional perturbations upon septic challenge.
Pathway Activity: At baseline, older lymphocytes showed suppressed metabolic pathways but elevated immune and proliferation-related pathways. Following sepsis, these pathways shifted in the opposite direction: metabolic pathways were exaggeratedly induced, while immune and proliferative pathways were disproportionately suppressed compared to young mice. T and NK cells in older mice also showed age-dependent enrichment of mitochondrial apoptotic pathways post-sepsis.
Intercellular Communication: Analysis of APC-to-T cell signaling revealed that while sepsis generally reduced signaling strength, older adult mice exhibited a relative preservation or even enhancement of specific co-stimulatory and antigen-presentation pathways (e.g., IL16, ICOS, ICAM, MHC-II, CD86) compared to young mice, which showed further declines.
Differentiation Dynamics: RNA velocity analysis indicated that sepsis accelerated B cell differentiation toward a mature plasma cell state. This acceleration was significantly more pronounced in older adult mice, aligning with the observed B cell depletion and plasma cell expansion.
Therapeutic Landscape: Drug-target mapping revealed that aging reshapes the druggable landscape in lymphocytes. Several drugs (e.g., bexarotene) showed age-dependent shifts in inferred target engagement after sepsis, indicating that the molecular networks accessible to therapeutics differ significantly between age groups.

Significance and Claims
The paper claims that aging, rather than sex, is the dominant host factor modifying the lymphoid immune response to sepsis in this murine model. The study highlights that aging does not merely attenuate the immune response but fundamentally redirects lymphoid remodeling toward a different cellular and transcriptional endpoint, particularly within humoral immune populations (B cells and plasma cells).

The authors propose that the "dysregulated aged baseline" creates a state of compromised metabolic readiness, which necessitates disproportionate activation under stress (sepsis). This leads to exaggerated transcriptional responses and functional exhaustion rather than effective immunity. Consequently, the study argues that precision immunotherapy for sepsis cannot rely on universal interventions; instead, therapeutic strategies must be age-stratified. The identification of specific metabolic and signaling checkpoints that differ by age offers potential targets for precision immunotherapy in older sepsis patients. The authors explicitly note that while sex effects were minimal in the lymphoid compartment in this study, they may be compartment-specific (as seen in their prior myeloid work) or temporally restricted, but age remains the primary driver of the observed lymphoid transcriptional override.

The Big Picture: A Tale of Two Defenses

The Main Discovery: Age is the Boss, Sex is a Sidekick

What Happened to the "Security Team"?

Summary of the Findings

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