Sepsis occurs when the body’s response to infection becomes dysregulated, triggering inflammation, vascular injury, altered circulation and widespread organ dysfunction. The kidneys are particularly vulnerable because they depend on a tightly controlled balance of blood flow, oxygen delivery, filtration and tubular transport. When acute kidney injury develops during sepsis, patients face increased risks of prolonged intensive-care treatment, dialysis and death. Yet clinicians often diagnose sepsis-associated acute kidney injury using measurements such as serum creatinine and urine output, indicators that describe impaired function but reveal little about the molecular events causing the damage.

The new work focuses on plasma proteomics, a technology that measures large numbers of proteins circulating in the blood. Plasma contains proteins released by immune cells, endothelial cells, injured tissues and organs responding to infection. Their concentrations and patterns can reflect inflammation, coagulation, vascular permeability, metabolism, tissue repair and cell death. Instead of examining one biomarker at a time, proteomic analyses compare coordinated protein signatures across many patients. Computational methods can then identify groups of patients whose molecular profiles resemble one another, potentially exposing biologically meaningful subtypes hidden within a conventional clinical diagnosis.

According to the study, this approach separated patients with sepsis-associated acute kidney injury into two subphenotypes that could be reproduced across analyses or patient groups. Reproducibility is a critical feature in biomarker research. A molecular pattern found in one hospital or one dataset may reflect local treatment practices, differences in patient selection or random statistical variation. A signature that persists under independent testing is more likely to represent a genuine feature of disease biology. The finding that two subphenotypes could be consistently recognized suggests that the division is not simply an artifact of a single experimental cohort.

The distinction is important because kidney injury during sepsis can arise through several overlapping mechanisms. Reduced effective circulation may limit oxygen delivery, while inflammatory signaling can disrupt the microcirculation and alter the behavior of endothelial cells lining blood vessels. Immune activation may damage the kidney directly or indirectly, and the kidney’s filtration units and tubular cells can respond differently to stress. At the same time, mitochondrial dysfunction, changes in cellular energy use, coagulation abnormalities and the accumulation of toxic metabolic products may contribute to declining renal function. Two patients with similar creatinine levels may therefore have very different combinations of these processes.

The study’s association between the two proteomic subphenotypes and distinct outcomes adds clinical weight to the molecular classification. The result indicates that the protein patterns were not merely descriptive labels; they corresponded to meaningful differences in how patients fared. The available citation does not specify the exact outcomes or the individual proteins defining each group, but the central message is clear: sepsis-associated acute kidney injury contains biologically distinct forms with different prognostic trajectories. That observation could eventually help clinicians identify patients at higher risk before conventional measures show the full extent of organ damage.

A major challenge in treating sepsis-associated kidney injury is that many interventions are applied to broad patient populations. Fluid administration, vasopressors, antimicrobial therapy and kidney replacement therapy are essential in appropriate circumstances, but the balance between benefit and harm may vary according to the underlying biological state. Excessive fluid can worsen tissue edema, while inadequate circulation can intensify kidney stress. Similarly, an anti-inflammatory or endothelial-targeted therapy might help one molecular subgroup but offer little benefit—or cause harm—in another. Proteomic subphenotyping could provide a framework for testing such treatments in more precisely defined populations.

The findings also illustrate why modern critical-care research is moving beyond single laboratory values. Creatinine rises slowly, is influenced by muscle mass and fluid balance, and may lag behind structural kidney injury. Urine output is clinically useful but can be affected by medications, hemodynamics and fluid management. A blood-based molecular signature could complement these measures by capturing active biological pathways closer to the time they begin. However, a proteomic classifier would need extensive validation before it could guide routine decisions. It would have to be rapid, affordable, standardized across laboratories and reliable in patients with different infections, ages, comorbidities and treatment exposures.

The study does not mean that sepsis-associated acute kidney injury can immediately be divided into two simple categories in everyday clinical practice. Proteomic patterns may represent points along a biological spectrum rather than completely separate diseases, and patients may shift from one state to another as infection and organ dysfunction evolve. Future investigations will need to identify the proteins and pathways that define the subphenotypes, determine when the signatures emerge, and establish whether they can predict outcomes early enough to change treatment. Researchers will also need to test whether matching therapies to molecular subgroups improves survival, accelerates kidney recovery or reduces the need for dialysis.

Even with those questions unresolved, the report marks an important step toward precision medicine in critical care. By showing that sepsis-associated acute kidney injury contains reproducible molecular subphenotypes with distinct outcomes, Legrand, Nguyen, Calfee and colleagues provide a more detailed map of a condition traditionally treated as one broad syndrome. The work may help explain why clinical trials in sepsis and acute kidney injury often produce inconsistent results: biologically different patients may have been grouped together under the same diagnosis. As proteomic technologies become faster and more accessible, blood-based molecular classification could help transform sepsis care from a largely uniform response into treatment guided by the specific biology unfolding inside each patient.

Subject of Research: Plasma proteomic subphenotypes of sepsis-associated acute kidney injury and their relationship to patient outcomes

Article Title: Plasma proteomics defines two reproducible subphenotypes of sepsis-associated acute kidney injury with distinct outcomes

Article References: Legrand, M., Nguyen, H., Calfee, C.S. et al. “Plasma proteomics defines two reproducible subphenotypes of sepsis-associated acute kidney injury with distinct outcomes.” Nature Communications (2026). https://doi.org/10.1038/s41467-026-76889-3

Image Credits: AI Generated

DOI: 10.1038/s41467-026-76889-3

Keywords: sepsis, acute kidney injury, plasma proteomics, subphenotypes, biomarkers, precision medicine, critical care, patient outcomes

Sepsis-associated acute kidney injury remains a formidable clinical challenge, frequently complicating severe systemic infections and contributing significantly to patient morbidity and mortality worldwide. The pathophysiology of SA-AKI is complex and multifactorial, involving inflammatory cascades, microvascular dysfunction, and immune responses that culminate in renal impairment. Conventional biomarkers such as serum creatinine and urine output are limited by their delayed responsiveness and insufficient specificity, underscoring the urgent need for more sensitive and early markers of kidney injury in septic patients.

What sets this study apart is its use of single urinary extracellular vesicle proteomics, a sophisticated approach that delves into the proteomic composition of vesicles shed into the urine by renal cells. These extracellular vesicles serve as miniature information packets, reflecting the molecular state of their parent cells. By isolating and analyzing individual vesicles rather than bulk urine samples, the researchers achieved an unprecedented resolution in detecting subtle changes in protein expression patterns that accompany kidney injury.

Through meticulous proteomic profiling, the team identified complement receptor CD35 as significantly elevated in the urinary extracellular vesicles of patients diagnosed with SA-AKI. CD35, also known as complement receptor 1 (CR1), plays a critical role in the immune system by regulating complement activation—a key component of innate immunity and inflammation. Its heightened presence in uEVs suggests an intimate link between complement-mediated immune pathways and the pathogenesis of septic kidney injury, providing a mechanistic insight into disease progression.

The implications of these findings are profound. Detecting CD35 in urinary extracellular vesicles could enable clinicians to diagnose SA-AKI at an earlier stage, potentially before irreversible renal damage occurs. Moreover, the specificity of CD35 to complement activation pathways offers opportunities to tailor therapeutics that modulate immune responses, potentially mitigating kidney injury in septic patients and improving survival rates.

This study also illustrates the transformative power of leveraging extracellular vesicles as non-invasive biomarkers. Unlike tissue biopsies, which are invasive and carry substantial risks, urinary vesicle analysis harnesses easily obtainable samples, facilitating repeated monitoring and dynamic assessment of disease states. The advancement of single-vesicle proteomics further enhances analytical precision, opening new horizons in personalized medicine for complex conditions such as sepsis.

The research team applied rigorous validation protocols, comparing uEV CD35 levels in diverse patient cohorts and correlating these measurements with established clinical parameters and outcomes. Such comprehensive analyses underscore the robustness of CD35 as a biomarker and set the stage for larger-scale clinical trials aimed at standardizing its use in critical care settings worldwide.

Beyond diagnostic applications, the study also sheds light on the molecular pathology of SA-AKI. The complement system’s double-edged role—essential for pathogen clearance yet potentially injurious when dysregulated—becomes vividly apparent. CD35’s association with urinary vesicles implies that renal cells actively engage in complement regulation, and perturbations in this process may signify early immunological distress within the kidney microenvironment.

From a technological standpoint, the deployment of next-generation mass spectrometry techniques in dissecting single urinary extracellular vesicles represents a formidable technical achievement. This allows not only for detection of protein abundance but also offers the potential to explore post-translational modifications, protein interactions, and vesicle heterogeneity that could further refine biomarker discovery and precision diagnostics.

The potential clinical impact of this discovery can hardly be overstated. Acute kidney injury occurs in up to 50% of septic patients in intensive care units, often worsening prognosis and complicating treatment algorithms. A biomarker that is both specific and accessible could transform critical care nephrology, enabling timing of interventions that preserve renal function and inform prognostic stratification, thus optimizing resource allocation and improving patient outcomes.

Moreover, the findings invite exploration into therapeutic targeting of the complement pathway, which has garnered attention in various inflammatory diseases but remains underexplored in sepsis-induced nephropathy. If CD35 modulation can be harnessed for therapeutic benefit, it could inaugurate novel drug development pathways grounded in molecular pathology illuminated by proteomic insights.

The study’s integrative approach highlights the importance of interdisciplinary collaboration among nephrologists, immunologists, proteomic scientists, and critical care specialists. This synthesis of expertise facilitates translation of complex molecular discoveries into tangible clinical applications, illustrating a model for future biomedical breakthroughs.

Looking forward, this research sets a precedent for expanding the landscape of urinary extracellular vesicle biomarkers in other acute and chronic kidney diseases. The identification of CD35 may be merely the first of many revelations enabled by high-resolution vesicle proteomics, promising a new era of non-invasive, precision nephrology where disease can be mapped and intercepted at the molecular level.

In summary, the identification of complement receptor CD35 in single urinary extracellular vesicles heralds a significant advance in the quest for early, specific biomarkers of sepsis-associated acute kidney injury. By marrying cutting-edge proteomics with clinical insight, Li, Tang, Gu, and colleagues offer renewed hope for vulnerable patient populations and invigorate the field’s ongoing pursuit of molecular diagnostics and targeted therapeutics.

As the scientific and medical communities continue to unravel the complex interplay between immunity and renal pathology in sepsis, the integration of uEV proteomics into routine clinical practice may soon become a reality. Such innovation not only promises to improve survival rates but also exemplifies the power of precision medicine approaches that decode disease signals from the tiniest particles within our bodily fluids.

This paradigm shift toward exploiting extracellular vesicles as diagnostic gold mines could soon extend beyond nephrology, influencing fields ranging from oncology to neurology. The approach championed by this study underscores the vast, largely untapped potential of vesicle-based biomarkers to revolutionize how we detect, monitor, and treat human disease.

Subject of Research: Identification of complement receptor CD35 as a biomarker for sepsis-associated acute kidney injury using single urinary extracellular vesicle proteomics.

Article Title: Single urinary extracellular vesicle proteomics identifies complement receptor CD35 as a biomarker for sepsis-associated acute kidney injury.

Article References:
Li, N., Tang, TT., Gu, M. et al. Single urinary extracellular vesicle proteomics identifies complement receptor CD35 as a biomarker for sepsis-associated acute kidney injury. Nat Commun 16, 6960 (2025). https://doi.org/10.1038/s41467-025-62229-4

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