Blood enzyme autotaxin tracks lupus activity and flags active kidney disease

Serum levels of the enzyme autotaxin are markedly elevated in patients with systemic lupus erythematosus and, according to a new cross-sectional study, rise sharply in those with active lupus nephritis, the kidney complication that was the study's particular focus. In the study, published in Egyptian Rheumatology and Rehabilitation, researchers at Assiut University in Egypt measured autotaxin in 60 adults with lupus and 30 age- and sex-matched healthy controls, finding that a single blood test distinguished patients from controls with an area under the curve of 0.989 and separated active kidney disease from quiescent renal status with an area under the curve of 0.992.

Autotaxin, encoded by the ENPP2 gene, is a lysophospholipase D enzyme that converts extracellular lysophospholipids into lysophosphatidic acid, a bioactive lipid mediator that signals through specific G protein-coupled receptors. The autotaxin–lysophosphatidic acid pathway participates in lymphocyte development and trafficking, cytokine secretion, fibroblast growth, and fibrotic processes, and targeting the pathway has been proposed as a therapeutic strategy in conditions such as renal fibrosis and interstitial lung disease. In lupus, the enzyme has drawn attention because plasmacytoid dendritic cells, the principal source of type I interferons, express ENPP2 at high levels, and interferon signaling stimulates autotaxin production, placing the lipid pathway at a suspected junction between genetic susceptibility and immune dysregulation in the disease.

The research team enrolled 60 adults who fulfilled the Systemic Lupus International Collaborating Clinics classification criteria, recruiting them from the Department of Rheumatology and Rehabilitation at Assiut University. The cohort comprised 51 women and 9 men with a mean age of 33.7 years, and the 30 controls, 25 women and 5 men with a mean age of 31.7 years, did not differ significantly from the patients in age or sex distribution.

Disease activity was scored with the SLE Disease Activity Index 2000, and renal involvement was graded with the renal SLEDAI-2K subscore, which assigns points for hematuria, pyuria, proteinuria, and urinary casts. Patients with a renal subscore of at least 4 were classified as having active lupus nephritis, while those scoring zero were classified as having no-renal activity. This split produced 31 patients in the active nephritis group and 29 in the no-renal activity group. All 31 patients with active nephritis underwent renal biopsy, with specimens classified by the revised International Society of Nephrology/Renal Pathology Society system and scored for histopathological activity and chronicity using the National Institutes of Health indices.

Serum autotaxin was quantified by sandwich enzyme-linked immunosorbent assay, with laboratory investigators blinded to clinical characteristics and samples identified only by numerical codes. Mean levels in the patients reached 2023.4 picograms per milliliter, roughly double the control mean of 932.5 picograms per milliliter, a difference that was highly significant. The spread among patients was wide, however, with a standard deviation of 1955.6 picograms per milliliter reflecting the influence of a subgroup with very high values. Patients with active lupus nephritis averaged 2694.9 picograms per milliliter, with individual values ranging up to 12,790, whereas patients with no-renal activity averaged 1305.5 picograms per milliliter, a level statistically indistinguishable from the controls.

Diagnostic performance analysis gave the study its most striking numbers. At a threshold above 1147 picograms per milliliter, serum autotaxin separated lupus patients from healthy controls with 96.7 percent sensitivity, 92.9 percent specificity, and 95 percent accuracy, with an area under the curve of 0.989 and a 95 percent confidence interval of 0.939 to 1. For the clinically harder question of distinguishing active nephritis from no-renal activity, a cut-off above 1571 picograms per milliliter yielded 90.3 percent sensitivity and perfect specificity, with an area under the curve of 0.992.

Regression modeling sharpened the picture of what drives the enzyme’s elevation. In univariate analysis, higher overall SLEDAI-2K scores, higher renal SLEDAI-2K scores, greater 24-hour urinary protein excretion, anti-double-stranded DNA positivity, and decreased complement C3 levels each predicted elevated autotaxin. But when these variables competed in a multivariate model, only the renal SLEDAI-2K score survived as an independent predictor, with a coefficient of 302.2 and a p value of 0.01. Serum autotaxin also correlated positively with C-reactive protein, blood urea nitrogen, and the liver enzymes AST and ALT, and negatively with hemoglobin and albumin, patterns the authors interpret as reflecting systemic inflammation, renal involvement, and protein loss rather than any single organ process.

Not every association pointed toward renal pathology. Autotaxin levels were significantly higher in patients with pericarditis or pericardial effusion, and in patients positive for antinuclear antibodies or anti-double-stranded DNA antibodies. Levels were also higher in patients treated with mycophenolate mofetil, which the authors attribute to greater disease severity rather than a drug effect, noting that the immunosuppressant does not directly inhibit the type I interferon pathway that regulates autotaxin expression. Intriguingly, autotaxin showed no significant differences across lupus nephritis histological classes and no significant correlation with biopsy activity or chronicity indices, a contrast with earlier work by Iwata and colleagues that reported lower serum autotaxin in class IV nephritis and inverse relationships with biopsy scores. The authors suggest circulating autotaxin tracks global immune activation rather than structural kidney damage, and that serum levels fluctuate with current activity while biopsy indices capture cumulative injury.

The mechanistic account the authors offer places autotaxin within the interferon axis central to lupus pathogenesis. Type I interferons enhance ENPP2 expression in immune cells, toll-like receptor-induced autotaxin production depends on interferon signaling, and interferon blockade reduces autotaxin expression, evidence for a reciprocal relationship between the lipid pathway and the interferon system. Transcriptomic studies have placed ENPP2 within interferon-associated gene networks in plasmacytoid dendritic cells from lupus patients, alongside genes linked to lupus susceptibility variants, although the authors caution that a direct causal relationship has not been established. In active nephritis, pro-inflammatory cytokines may upregulate autotaxin production, and the resulting lysophosphatidic acid signaling may recruit inflammatory cells into the kidney, while mesangial and tubular epithelial cells may add local production in response to injury.

The findings arrive with clear caveats that the authors themselves enumerate. The sample was small, the design cross-sectional, the setting a single center, and there was no longitudinal follow-up, no external validation cohort, and no disease-control groups with other autoimmune conditions. Urinary autotaxin was not measured, an omission the authors flag as significant given prior reports that urinary levels rise in lupus nephritis and may better reflect renal inflammation. Age and body mass index correlated inversely with autotaxin in this cohort, patterns the authors attribute to disease activity and treatment exposure rather than physiology, since autotaxin normally correlates positively with adiposity. Within those limits, the study positions serum autotaxin as a promising non-invasive marker of lupus disease activity with its strongest signal in renal involvement, and the authors call for larger prospective studies measuring both serum and urinary autotaxin to determine whether the near-perfect discrimination observed here holds up in broader populations.

Subject of Research: Serum autotaxin as a biomarker of disease activity and renal involvement in systemic lupus erythematosus

Article Title: Clinical utility of serum autotaxin in systemic lupus erythematosus: association with disease activity and renal involvement

Article References: Selim, Z. I., Abdelrahman, M. S. I., Abd-Elrazik, M. M., Badawy, E. R., & Gamal, N. M. (2026). Clinical utility of serum autotaxin in systemic lupus erythematosus: association with disease activity and renal involvement. Egyptian Rheumatology and Rehabilitation, 53(1), Article 80. https://doi.org/10.1186/s43166-026-00451-8

Image Credits: AI Generated

DOI: 10.1186/s43166-026-00451-8

Keywords: systemic lupus erythematosus, autotaxin, lupus nephritis, biomarker, SLEDAI-2K, lysophosphatidic acid, type I interferon, plasmacytoid dendritic cells, ELISA, renal disease activity, ROC analysis, cross-sectional study