Renal Macrophage Shifts Drive Glomerulosclerosis in Lupus Nephritis Progression

Navigating the Transition from Inflammation to Fibrosis in Lupus Nephritis

Lupus nephritis affects approximately 50% of patients with systemic lupus erythematosus and remains a primary driver of morbidity, often progressing to end-stage renal disease despite modern immunosuppressive regimens [1, 2, 3]. While biological agents such as belimumab have improved complete renal response rates (relative risk 1.47, 95% confidence interval 1.07 to 2.02), achieving rapid remission remains a significant clinical challenge [4, 5]. Current management relies on the National Institutes of Health chronicity index (a histological scoring system used to quantify permanent renal scarring) to guide prognosis, yet the transition from reversible inflammation to fibrosis is poorly understood [3, 6]. Elevated levels of interleukin-18 (a pro-inflammatory cytokine and pyroptosis effector) are strongly associated with renal injury, particularly in class IV lupus nephritis (standardized mean difference 2.51, p < 0.001), highlighting the persistent inflammatory burden [7]. A recent analysis using single-cell RNA-sequencing (a technique that identifies gene expression in individual cells) and spatial transcriptomics (a method that maps gene activity to specific tissue locations) reveals that disease-specific macrophages interact with parietal epithelial cells to promote glomerulosclerosis as tissue damage accumulates [3].

Mapping the Myeloid Landscape in the Lupus Kidney

To characterize the cellular drivers of renal decline, researchers analyzed single-cell RNA-sequencing data from dissociated kidney samples of 156 patients with lupus nephritis. This transcriptomic analysis, which identifies gene expression profiles at the level of individual cells, was compared against a control group of 30 healthy individuals. By examining these high-resolution cellular signatures, the study generated a comprehensive catalogue of myeloid subsets found in lupus nephritis kidneys. This atlas provides a foundational tool for understanding the histologic heterogeneity of the disease, allowing clinicians to see how specific immune cell populations fluctuate as the pathology progresses from acute inflammation to chronic scarring. The researchers further refined these findings by applying spatial transcriptomics to kidney samples from 6 patients with lupus nephritis and 2 controls. Spatial transcriptomics maps gene activity to specific tissue locations, allowing investigators to see exactly where immune cells are positioned within the renal architecture. The gene panel used for this spatial analysis was specifically designed to capture all myeloid subsets identified in the single-cell RNA-sequencing data, ensuring that localized findings matched the broader cellular atlas. This dual-modality approach confirmed that as the National Institutes of Health chronicity index increases, indicating irreversible tissue damage, the local immune response shifts. The environment moves from one dominated by monocytes and macrophages toward an expansion of CD4 T cells, GZMK-positive CD8 T cells, B cells, and dendritic cells. For the practicing nephrologist or rheumatologist, this provides a clear link between specific immune cell infiltration and the progression of renal fibrosis, suggesting that targeted therapies may eventually need to be timed according to the dominant cellular infiltrate.

The Shift from Myeloid Inflammation to Lymphocytic Chronicity

The researchers utilized the National Institutes of Health chronicity index, a standardized histological scoring system used to quantify permanent renal scarring, to track how immune cell populations evolve during the progression of lupus nephritis. Their analysis revealed that as chronicity index scores increase, the renal microenvironment undergoes a fundamental reorganization. The initial immune response, which is primarily dominated by monocytes and macrophages, gradually gives way to a more complex cellular landscape. This transition is marked by a significant expansion of CD4 T cells and GZMK-positive CD8 T cells (cytotoxic T cells characterized by the expression of granzyme K). Alongside these T cell subsets, the study identified a concurrent increase in B cells and dendritic cells (specialized antigen-presenting cells). This suggests that the chronic phase of the disease is driven by a distinct lymphocytic profile rather than the myeloid-heavy infiltration seen in early, active lesions. This cellular evolution has direct implications for understanding the molecular signaling that sustains renal injury. The researchers observed that the transition to a lymphocyte-dominated response is accompanied by a parallel decrease in the interferon response, a molecular signature of type I interferon signaling that typically characterizes acute systemic lupus erythematosus flares. This finding suggests that while interferon-driven inflammation may initiate the damage, the subsequent accumulation of irreversible tissue damage is associated with a waning of this specific pathway as chronic scarring takes hold. For the practicing clinician, these data highlight a critical window where the underlying pathophysiology of lupus nephritis shifts. This evolution potentially alters the efficacy of therapies that target specific immune pathways, indicating that anti-interferon agents might be less effective as the disease moves toward a higher National Institutes of Health chronicity index.

Disease-Specific Macrophages and the Path to Glomerulosclerosis

The researchers identified that in cases of proliferative or mixed lupus nephritis, the degree of active inflammation correlates directly with the expansion of disease-specific macrophage subsets. These specialized myeloid cells appear to be central to the acute phase of renal injury. However, as the disease progresses and permanent damage accumulates, these disease-specific macrophage subsets contract as the National Institutes of Health chronicity index increases. This inverse relationship suggests that these macrophages are most active during the inflammatory peak and may be responsible for initiating the transition toward chronic tissue failure. To understand where these cells originate, the authors employed trajectory analysis (a computational method used to determine the lineage or state transitions of cells based on their genetic expression over time). This analysis suggested that disease-specific macrophages arise from both infiltrating monocytes and tissue-resident macrophages, indicating a dual origin from both the systemic circulation and the local kidney environment. The findings regarding this dual origin were further supported by spatial transcriptomics data and cell cultures, which confirmed that both local and recruited precursors contribute to the disease-specific macrophage pool. The study further elucidated the mechanism of renal decline by mapping the physical and molecular proximity of these cells within the kidney. The data imply that disease-specific macrophages interact with parietal epithelial cells (the cells lining the Bowman capsule). This specific cellular crosstalk is clinically significant because the interaction between disease-specific macrophages and parietal epithelial cells promotes the development of glomerulosclerosis, the irreversible scarring of the kidney filtering units. For the clinician, these results clarify the cellular drivers of renal scarring, suggesting that the optimal window for preventing permanent glomerulosclerosis may be tied to the period when these disease-specific macrophages are most expanded, well before the National Institutes of Health chronicity index begins its terminal rise.

References

1. Hurd K, Barnabe C. Mortality causes and outcomes in Indigenous populations of Canada, the United States, and Australia with rheumatic disease: A systematic review.. Seminars in arthritis and rheumatism. 2018. doi:10.1016/j.semarthrit.2017.07.009

2. Desai SB, Ahdoot R, Malik F, Obert M, Hanna R. New guidelines and therapeutic updates for the management of lupus nephritis.. Current opinion in nephrology and hypertension. 2024. doi:10.1097/MNH.0000000000000969

3. Hoover PJ, Eisenhaure TM, Hodgin J, et al. Deep profiling of lupus nephritis kidneys reveals dynamic changes in myeloid cells associated with disease progression.. Annals of the rheumatic diseases. 2026. doi:10.1016/j.ard.2026.03.004

4. Zhang H, Chen J, Zhang Y, Zhao N, Xu D. Efficacy and safety of belimumab therapy in lupus nephritis: a systematic review and meta-analysis. Renal Failure. 2023. doi:10.1080/0886022X.2023.2207671

5. Mok CC, So H, Hamijoyo L, et al. The 2024 APLAR Consensus on the Management of Lupus Nephritis.. International journal of rheumatic diseases. 2025. doi:10.1111/1756-185X.70021

6. Barcelos NEDS, Limeres ML, Peixoto-Dias AF, Vieira MAR, Peruchetti DB. Kidney Disease and Proteomics: A Recent Overview of a Useful Tool for Improving Early Diagnosis.. Advances in experimental medicine and biology. 2024. doi:10.1007/978-3-031-50624-6_9

7. Zhou C, Li J, Zhao J, Bai X, Shang S, Li W. Interleukin-18 in lupus nephritis: a meta-analysis of cytokine signaling dysregulation in immune-mediated nephropathy.. Frontiers in immunology. 2025. doi:10.3389/fimmu.2025.1631728