Steady-State Tissue Oxygen Distributions Calculated by a Green's Function Method and a Finite Difference Method: A Comparison

Simulations that are meant to determine the steady-state distribution of a diffusible solute such as oxygen in tissues have typically used finite difference methods to solve the diffusion equation. Finite difference methods require a tissue mesh with enough points to resolve oxygen gradients near and between discrete blood vessels. The large number of points that are typically required can make these calculations very slow. In this paper, we investigate a numerical method known as the Green's function method which is not bound by the same constraint. The Green's function method is expected to yield an accurate oxygen distribution more quickly by requiring fewer mesh points. Both methods were applied to calculate the steady state oxygen distribution in a model simulation region. When the Green's function calculation used meshes with 1/2, 1/4 and, 1/8 of the resolution required for the finite-difference mesh, there was good agreement with the finite difference calculation in all cases. When the volume of the domain was increased 8-fold the Green's function method was able to calculate the O₂ field in 22 minutes, whereas the finite difference calculation is expected to take approximately 1 week. The number of steps required for the Green's function calculation increases quadratically with the number of points in the tissue mesh. As a result, small meshes are calculated very quickly using Green's functions, while for larger mesh sizes this method experiences a significant decrease in efficiency.

Cutaneous vasculitis in SLE

Objectives

We determined the temporal association between clinical and serological disease manifestations and development of cutaneous small vessel vasculitis in a large prospective multiethnic cohort.

Methods

Patients with SLE diagnosed according to the Systemic Lupus International Collaborating Clinics (SLICC) classification criteria or the revised classification criteria as defined by the American College of Rheumatology (ACR) were enrolled in the Hopkins Lupus Cohort. Cutaneous small vessel vasculitis was determined as a component of the Systemic Lupus Erythematosus Disease Activity Index. SLE-associated cutaneous small vessel vasculitis lesions were reported clinically. They presented as punctate lesions, palpable purpura, tender erythematous plaques or macules with or without necrosis. No histopathological diagnosis was pursued to confirm the diagnosis of vasculitis or to differentiate it from other causes of digital lesions in patients with SLE. Disease manifestations that preceded the first occurrence of cutaneous small vessel vasculitis lesions were analysed using Kaplan-Meier. Cox regression analysis was used to assess the relationship between baseline clinical and immunological manifestations and the development of cutaneous small vessel vasculitis. We adjusted for gender, race and age at SLE diagnosis.

Results

A total of 2580 patients were studied: 52.4% were Caucasian and 39.4% were African-American. The mean age of the cohort was 45.5±14.5 years. The mean years of cohort follow-up was 7.9±7.6. Cutaneous small vessel vasculitis was observed in 449 (17.3%). The mean time to cutaneous vasculitis after SLE diagnosis was 4.78 years (95% CI 3.96 to 5.60). At least 159 (35%) patients had recurrences of cutaneous vasculitis lesions. Discoid rash, Raynaud’s phenomenon, myositis, anaemia, Coombs’ positivity, leucopenia, anti-Smith and anti-RNP (Ribonucleoprotein) were significantly associated with the development of cutaneous vasculitis. The SLICC/ACR Damage Index score was higher in patients with cutaneous vasculitis compared with those without cutaneous vasculitis.

Conclusions

Cutaneous vasculitis is frequent (17.3%) and often recurrent (35%). African-Americans are at higher risk of developing cutaneous small vessel vasculitis than Caucasians. Clinical presentations such as myositis and haematological manifestations are predictors of cutaneous vasculitis development. The presence of cutaneous vasculitis is associated with increased organ damage.

OP0160 HYDROXYCHLOROQUINE BLOOD LEVELS AND RISK OF THROMBOTIC EVENTS IN SYSTEMIC LUPUS ERYTHEMATOSUS

Background:

Hydroxychloroquine (HCQ) has a primary role in the treatment of systemic lupus erythematous (SLE). Beyond its pleiotropic immunomodulatory effects on Toll-like receptor and type I interferon signaling, HCQ use has been found to be protective for thrombosis in SLE (1). Optimal dosing of HCQ in SLE is unknown. The longitudinal measurement of HCQ blood levels may provide an opportunity to individualize weight-based dosing strategies and reduce risk of toxicity.

Objectives:

Examine the association of HCQ blood levels with thrombotic events in a longitudinal SLE cohort.

Methods:

812 SLE patients with HCQ blood level measured prior to the thrombosis were included: 93% female, 43% African-American, 46% Caucasian. HCQ blood levels were quantified by liquid chromatography-tandem mass spectrometry. Mean HCQ blood levels (± standard deviation) over all cohort visits prior to occurrence of thrombosis were calculated for each patient. Thromboses were defined as venous (DVT/PE or other venous) or arterial thrombosis (stroke, myocardial infarction, digital gangrene or other arterial).

Results:

Thrombosis had occurred during prospective follow up in 43 patients (5.5%), venous in 3.0% and arterial in 2.9%. Lupus anticoagulant was strongly associated with a history of any thrombosis (OR 3.25, p<0.0001), venous thrombosis (OR 3.53, p<0.0001), and arterial thrombosis (OR 3.08, p<0.0001). A prospective analysis shows that for any thrombosis and for venous thrombosis, the HCQ blood level was significantly lower (Table 1). Higher prescribed doses of HCQ (as opposed to HCQ blood levels) were also associated with decreased odds of any thrombosis and venous thrombosis in a separate cross-sectional analysis (OR 0.88, p=0.04 and OR 0.83, p=0.009, respectively for each 1 mg/kg increase in prescribed HCQ).

Table 1.

Thrombotic Events are Associated with Lower Mean HCQ Blood Level

Mean HCQ Blood Level (± Std. Dev.)Thrombotic EventNo EventP-valueAny thrombosis695 ±464887 ± 5620.029Any venous thrombosis682 ± 374881 ± 5600.10DVT/PE only615 ± 384881 ± 5590.055Any arterial thrombosis708 ± 539882 ± 5580.13Stroke720 ± 643880 ± 5570.27

Conclusion:

HCQ blood levels are inversely associated with risk of any thrombosis and of venous thrombosis in patients with SLE in a prospective analysis. Reduction of HCQ dosing, as suggested by the American Academy of Ophthalmologists (2), could reduce or eliminate the benefit of hydroxychloroquine to prevent thrombosis.

References:

[1]Petri M. Use of hydroxychloroquine to prevent thrombosis in systemic lupus erythematosus and in antiphospholipid antibody–positive patients. Curr Rheumatol Rep 2011;13:77–80.

[2]Marmor MF, Kellner U, Lai TYY, Melles RB, Mieler WF. Recommendations on screening for chloroquine and hydroxychloroquine retinopathy (2016 revision). Ophthalmology 2016;123:1386–1394.

Acknowledgments:

The Hopkins Lupus Cohort is supported by NIH Grant RO1 AR069572

Disclosure of Interests:

Michelle A Petri Grant/research support from: GSK, Eli Lilly and Company, Consultant of: Eli Lilly and Company, Maximilian Konig: None declared, Jessica Li: None declared, Daniel Goldman: None declared

Tgfb3 collaborates with PP2A and notch signaling pathways to inhibit retina regeneration

Neuronal degeneration in the zebrafish retina stimulates Müller glia (MG) to proliferate and generate multipotent progenitors for retinal repair. Controlling this proliferation is critical to successful regeneration. Previous studies reported that retinal injury stimulates pSmad3 signaling in injury-responsive MG. Contrary to these findings, we report pSmad3 expression is restricted to quiescent MG and suppressed in injury-responsive MG. Our data indicates that Tgfb3 is the ligand responsible for regulating pSmad3 expression. Remarkably, although overexpression of either Tgfb1b or Tgfb3 can stimulate pSmad3 expression in the injured retina, only Tgfb3 inhibits injury-dependent MG proliferation; suggesting the involvement of a non-canonical Tgfb signaling pathway. Furthermore, inhibition of Alk5, PP2A or Notch signaling rescues MG proliferation in Tgfb3 overexpressing zebrafish. Finally, we report that this Tgfb3 signaling pathway is active in zebrafish MG, but not those in mice, which may contribute to the different regenerative capabilities of MG from fish and mammals.

Enrichment Preferences of Singly Housed Zebrafish (Danio rerio)

Despite the increasing popularity of zebrafish (Danio rerio) as an animal model, the environmental enrichment preferences of this species have been largely unexplored. We sought to determine the preferences of mature female zebrafish that were singly housed with or without access to one of 10 inanimate forms of enrichment. As a marker of preference, in-tank fish location was observed by video recording. All subjects showed a preference for the front of the tank when caretakers entered the room, demonstrating an effect of human presence on tank location. Among the 10 enrichment items tested, subjects showed the strongest preference for mirrored paper on the side of the tank when compared with the barren half of the tank. Fish also were observed interacting with PVC pipe, marbles, and tulle. Given the preference for enrichment imitating social interaction, we conducted a second study to assess the value of visual exposure of conspecifics in adjacent tanks. The experimental zebrafish were then provided one of 3 conditions-a singly housed neighbor fish, group-housed neighbor fish, or no neighbor fish. All zebrafish housed next to neighboring fish showed a preference to be on the side of the tank nearer to the other fish. Overall, our data indicate that singly housed zebrafish prefer enrichment items that resemble or promote social behaviors. Therefore items such as mirrored paper or housing next to conspecifics should be strongly considered as enrichment strategies for singly housed zebrafish.

Time to Lupus Low Disease Activity State in the Hopkins Lupus Cohort: Role of African American Ethnicity

OBJECTIVE

Lupus low disease activity state (LLDAS) is a potential treat-to-target goal in systemic lupus erythematosus (SLE). This study determined predictors of time to reach LLDAS in a longitudinal cohort.

METHODS

Patients were grouped according to LLDAS status at cohort entry. Those who did not satisfy LLDAS at cohort entry were analyzed prospectively. The Kaplan-Meier approach was used to estimate the time to LLDAS. Cox regression was used to identify patient characteristics that were associated with time to LLDAS.

RESULTS

The probability of LLDAS attainment within 1 year was 52% for Caucasians, 36% for African Americans, and 33% for SLE patients with renal involvement. The median time to LLDAS was 1.1 years. In multivariable models, African American ethnicity, baseline prednisone >10 mg daily, hypocomplementemia, baseline damage, and baseline renal activity remained significant predictors of longer time to attain LLDAS, while disease duration <1 year and cutaneous activity were associated with earlier attainment.

CONCLUSION

LLDAS is potentially attainable in the majority of SLE patients. The time to LLDAS was found to be longer in African American patients with SLE. Characteristics of African American patients with SLE, such as renal activity and hypocomplementemia, were also independent predictors of slower attainment of LLDAS. These findings point to the need to include African American patients with SLE in both clinical and pharmaceutical research.

Autoantibody clustering of lupus-associated pulmonary hypertension

Objective

To define the SLE phenotype associated with pulmonary hypertension using multiple autoantibodies.

Methods

207 (8%) patients with SLE with pulmonary hypertension, defined as a right ventricular systolic pressure greater than 40 mm Hg on transthoracic echocardiogram or as pulmonary artery dilatation on CT of the chest, were identified from the Hopkins Lupus Cohort (94.2% female; 56.5% African–American, 39% Caucasian; mean age 45.6 years). 53 patients were excluded from the clustering analysis due to incomplete autoantibody profiles. Agglomerative hierarchical clustering algorithm with Ward’s method was used to cluster the patients with pulmonary hypertension, based on their autoantibodies. Autoantibodies used in the clustering analysis included lupus anticoagulant, anticardiolipin, anti-beta 2 glycoprotein I, antidouble-stranded DNA, anti-Sm (anti-Smith), antiribonucleoprotein, false positive-rapid plasma reagin, anti-Ro, anti-La and hypocomplementaemia (C3 ever low or C4 ever low). The Dunn index was used to internally validate the clusters. Bootstrap resampling derived the mean Jaccard coefficient for each cluster. All analyses were performed in R V.3.6.1 using the packages cluster, fpc and gplots.

Results

A significantly higher prevalence of pulmonary hypertension in African–American patients with SLE, compared with Caucasian patients with SLE (11.5% vs 5.9%, p<0.0001), was found. Based on equivalent Dunn indices, the 154 patients with SLE-associated pulmonary hypertension with complete autoantibody data were divided into five clusters, three of which had mean Jaccard coefficients greater than 0.6. Hypocomplementaemia, renal disorder and age at diagnosis significantly differed across clusters. One cluster was defined by antiphospholipid antibodies. One cluster was defined by anti-Ro and anti-La. One cluster had low frequencies of all antibodies.

Conclusion

SLE-associated pulmonary hypertension disproportionately affects African–American patients. Pulmonary hypertension in SLE is defined by five autoantibody clusters. Antiphospholipid antibodies, anti-Ro and anti-La positivity, serological activity, and age at pulmonary hypertension diagnosis significantly differed across clusters, possibly indicating different pathophysiological mechanisms.

Predictors of predominant Lupus Low Disease Activity State (LLDAS-50)

AIM

The Lupus Low Disease Activity State (LLDAS) is a potential treat to target goal in systemic lupus erythematosus (SLE). SLE patients in LLDAS for more than half of the observation time have about a 50% lower risk of new organ damage and have reduced mortality. We identified predictors of being in LLDAS ≥50% of the observation time.

METHODS

A total of 2228 SLE patients who had at least three clinical visits were included. Percentage of time in LLDAS was calculated based on the proportion of days under observation. LLDAS-50 was defined as being in LLDAS for ≥50% of the observation time. We used the stepwise selection procedure in logistic regression to identify predictors of LLDAS-50.

RESULTS

A total of 1169 (52.5%) SLE patients, but only 37.6% of African Americans, achieved LLDAS-50. In the multivariable model, African American ethnicity, hypocomplementemia, serositis, renal activity, arthritis, anti-RNP, anti-dsDNA, vasculitis, malar rash, discoid rash, thrombocytopenia, and immunosuppressive use were negative predictors of LLDAS-50. Older age at diagnosis, longer disease duration, higher education level, and greater percentage of time taking hydroxychloroquine remained positive predictors of LLDAS-50.

CONCLUSION

In this large cohort, only 52.5% achieved LLDAS-50. This proportion was even less in African Americans. A higher percentage of time taking hydroxychloroquine was a modifiable positive predictor of LLDAS-50. Anti-RNP, anti-dsDNA, and low complement were negatively associated with LLDAS-50. Our findings further emphasize the importance of inclusion of African Americans in clinical trials and hydroxychloroquine adherence in both clinical practice and clinical trials.

Differential Treatments Based on Drug-induced Gene Expression Signatures and Longitudinal Systemic Lupus Erythematosus Stratification

Systemic lupus erythematosus (SLE) is a heterogeneous disease with unpredictable patterns of activity. Patients with similar activity levels may have different prognosis and molecular abnormalities. In this study, we aimed to measure the main differences in drug-induced gene expression signatures across SLE patients and to evaluate the potential for clinical data to build a machine learning classifier able to predict the SLE subset for individual patients. SLE transcriptomic data from two cohorts were compared with drug-induced gene signatures from the CLUE database to compute a connectivity score that reflects the capability of a drug to revert the patient signatures. Patient stratification based on drug connectivity scores revealed robust clusters of SLE patients identical to the clusters previously obtained through longitudinal gene expression data, implying that differential treatment depends on the cluster to which patients belongs. The best drug candidates found, mTOR inhibitors or those reducing oxidative stress, showed stronger cluster specificity. We report that drug patterns for reverting disease gene expression follow the cell-specificity of the disease clusters. We used 2 cohorts to train and test a logistic regression model that we employed to classify patients from 3 independent cohorts into the SLE subsets and provide a clinically useful model to predict subset assignment and drug efficacy.

Hyperinsulinemia does not cause de novo capillary recruitment in rat skeletal muscle

Objective

The effect of insulin on blood flow distribution within muscle microvasculature has been suggested to be important for glucose metabolism. However, the “capillary recruitment” hypothesis is still controversial and relies on studies using indirect contrast‐enhanced ultrasound (CEU) methods.

Methods

We studied how hyperinsulinemia effects capillary blood flow in rat extensor digitorum longus (EDL) muscle during euglycemic hyperinsulinemic clamp using intravital video microscopy (IVVM). Additionally, we modeled blood flow and microbubble distribution within the vascular tree under conditions observed during euglycemic hyperinsulinemic clamp experiments.

Results

Euglycemic hyperinsulinemia caused an increase in erythrocyte (80 ± 25%, P < .01) and plasma (53 ± 12%, P < .01) flow in rat EDL microvasculature. We found no evidence of de novo capillary recruitment within, or among, capillary networks supplied by different terminal arterioles; however, erythrocyte flow became slightly more homogenous. Our computational model predicts that a decrease in asymmetry at arteriolar bifurcations causes redistribution of microbubble flow among capillaries already perfused with erythrocytes and plasma, resulting in 25% more microbubbles flowing through capillaries.

Conclusions

Our model suggests increase in CEU signal during hyperinsulinemia reflects a redistribution of arteriolar flow and not de novo capillary recruitment. IVVM experiments support this prediction showing increases in erythrocyte and plasma flow and not capillary recruitment.

Morphological variation suggests that chitinozoans may be fossils of individual microorganisms rather than metazoan eggs

Chitinozoans are organic-walled microfossils widely recorded in Ordovician to Devonian (ca 485–359 Mya) marine sediments and extensively used in high-resolution biostratigraphy. Their biological affinity remains unknown, but most commonly, they are interpreted as eggs of marine metazoans. Here, we provide new insights into their palaeobiology from three lines of inquiry. We examine morphological variation of a new, well-preserved Late Ordovician species, Hercochitina violana; analyse a compiled dataset of measurements on 378 species representing all known chitinozoan genera; and compare these data with the size variation of eggs of both extinct and extant aquatic invertebrates. The results indicate that the magnitude of size variation within chitinozoan species is larger than observed in fossil and modern eggs. Additionally, delicate morphological structures of chitinozoans, such as prosome and complex ornamentation, are inconsistent with the egg hypothesis. Distinct and continuous morphological variation in H. violana is more plausibly interpreted as an ontogenetic series of individual microorganisms, rather than as eggs.

mTORC1 underlies age-related muscle fiber damage and loss by inducing oxidative stress and catabolism

Aging leads to skeletal muscle atrophy (i.e., sarcopenia), and muscle fiber loss is a critical component of this process. The mechanisms underlying these age-related changes, however, remain unclear. We show here that mTORC1 signaling is activated in a subset of skeletal muscle fibers in aging mouse and human, colocalized with fiber damage. Activation of mTORC1 in TSC1 knockout mouse muscle fibers increases the content of morphologically abnormal mitochondria and causes progressive oxidative stress, fiber damage, and fiber loss over the lifespan. Transcriptomic profiling reveals that mTORC1's activation increases the expression of growth differentiation factors (GDF3, 5, and 15), and of genes involved in mitochondrial oxidative stress and catabolism. We show that increased GDF15 is sufficient to induce oxidative stress and catabolic changes, and that mTORC1 increases the expression of GDF15 via phosphorylation of STAT3. Inhibition of mTORC1 in aging mouse decreases the expression of GDFs and STAT3's phosphorylation in skeletal muscle, reducing oxidative stress and muscle fiber damage and loss. Thus, chronically increased mTORC1 activity contributes to age-related muscle atrophy, and GDF signaling is a proposed mechanism.

Granulin 1 Promotes Retinal Regeneration in Zebrafish

Purpose

Retinal degenerative diseases can progress to severe reductions of vision. In general, the changes are permanent in higher vertebrates, including humans; however, retinal regeneration can occur in lower vertebrates, such as amphibians and teleost fish. Progranulin is a secreted growth factor that is involved in normal development and wound-healing processes. We have shown that progranulin promotes the proliferation of retinal precursor cells in mouse retinas. The purpose of this study was to investigate the role played by granulin 1 (grn1) in the retinal regeneration in zebrafish.

Methods

We injured the retina of zebrafish with needle puncturing, and the retinas were examined at different times after the injury. We also checked the proliferation and the expression of retinal regeneration–related genes after knockdown of grn1 by electroporation with morpholino oligonucleotides (MO) and intravitreal injection of recombinant grn1.

Results

Our results showed that the level of grn1 was highly increased after retinal injury, and it was expressed in various types of retinal cells. A knockdown of grn1 reduced the proliferation of Müller glial cells in zebrafish eyes undergoing retinal regeneration. The knockdown of grn1 also reduced the expression of achaete-scute homolog 1a (ascl1a), an important factor in retinal regeneration. An intravitreal injection of recombinant grn1 led to a proliferation of Müller glial cells and an increase in the expression of retinal regeneration–related genes, such as ascl1a and lin28.

Conclusions

These findings suggested that grn1 should be considered as a target for stimulating the dedifferentiation of Müller glial cells and retinal regeneration.

Quadrivalent versus trivalent influenza vaccine: clinical outcomes in two influenza seasons, historical cohort study

OBJECTIVES

The quadrivalent influenza vaccine (QIV) contains two influenza B antigens (one of each B lineage), while the trivalent vaccine (TIV) contains solely one. As a result, a mismatch between the circulating B lineage and the lineage in the TIV occurs frequently. We aimed to compare the frequency of clinically significant outcomes in a large cohort of vaccinees receiving either TIV or QIV.

METHODS

Historical cohort study of all inactivated influenza vaccinees (aged 3 years and older) in a Health Maintenance Organization insuring 1.2 million individuals, over two influenza seasons in which both vaccines were provided non-selectively. Primary outcome was hospital admissions during the influenza season. Multivariate analysis was performed using logistic regression to adjust for relevant covariates.

RESULTS

Our cohort included 150 518 and 168 296 vaccinees in the first (S1) and second season (S2), respectively. The two influenza seasons were characterized by high Influenza B activity. Of those vaccinated with QIV, 2074 of 49 726 (4.2%) and 6563 of 121 741 (5.4%) were hospitalized compared with 7378 of 100 792 (7.3%) and 3372 of 46 555 (7.2%) of those vaccinated with TIV (S1 and S2, respectively). After multivariate analysis adjusting for several covariates (gender, age, socioeconomic status, chronic morbidity, timing of vaccination), compared with TIV recipients, QIV vaccinees had lower odds for hospitalization (OR = 0.92, 95% CI 0.87-0.98 and OR = 0.89, 95% CI 0.85-0.93) or emergency department visit (OR = 0.91, 95% CI 0.87-0.95 and OR = 0.84, 95% CI 0.81-0.87) in S1 and S2, respectively (p < 0.001). Lower odds of mortality and influenza-like illness were also observed in S2 (OR = 0.61, 95% CI 0.50-0.75 and OR = 0.92, 95% CI 0.90-0.95, respectively).

CONCLUSIONS

In seasons with relatively high influenza B activity, QIV appeared more protective than TIV in Israel.

Endogenous dipeptidyl peptidase IV modulates skeletal muscle arteriolar diameter in rats

The purpose of this study is to investigate that dipeptidyl peptidase IV (DPP‐IV) released from skeletal and vascular smooth muscle can increase arteriolar diameter in a skeletal muscle vascular bed by reducing neuropeptide Y (NPY)‐mediated vasoconstriction. We hypothesized that the effect of myokine DPP‐IV would be greatest in the smallest and least in the largest arterioles. Eight male Sprague Dawley rats (age 7–9 weeks; mass, mean ± SD: 258 ± 41 g) were anesthetized and the gluteus maximus dissected in situ for intravital microscopy analysis of arteriolar diameter of the vascular network. Computational modeling was performed on the diameter measurements to evaluate the overall impact of diameter changes on network resistance and flow distribution. In the first set of experiments, whey protein isolate powder was added to physiological saline solution, put in a heated reservoir, and applied to the preparation to induce release of DPP‐IV from the muscle. This resulted in an order‐dependent increase in arteriolar diameter, with the largest change in the 6A arterioles (63% more reactive than 1A arterioles; P < 0.05). This effect was abolished by adding the DPP‐IV inhibitor, Diprotin A. To test if the DPP‐IV released was affecting NPY‐mediated vasoconstriction, we applied NPY and whey protein, which resulted in attenuated vasoconstriction. These findings suggest that DPP‐IV is released from muscle and has a unique effect on blood flow, which appears to act on NPY to attenuate vasoconstriction. The findings suggest that DPP‐IV released from the skeletal or smooth muscle can alter muscle blood flow.

Stratification of Systemic Lupus Erythematosus Patients Into Three Groups of Disease Activity Progression According to Longitudinal Gene Expression

OBJECTIVE

The highly heterogeneous clinical presentation of systemic lupus erythematosus (SLE) is characterized by the unpredictable occurrence of disease flares and organ damage. Attempts to stratify lupus patients have been limited to classification based on clinical information, leading to unsuccessful clinical trials and controversial research results. This study was undertaken to develop and validate a robust method to stratify patients with lupus according to longitudinal disease activity and whole-genome gene expression data in order to establish subgroups of patients who share disease progression mechanisms.

METHODS

We used a cluster-based approach to stratify SLE patients based on the correlation between disease activity scores and longitudinal gene expression information. Clustering robustness was evaluated by the bootstrap method, and the clusters were characterized in terms of clinical and functional features.

RESULTS

We observed a clear partition into 3 different disease clusters in 2 independent sets of patients, one pediatric and one adult, which was not influenced by treatment, race, or other source of bias. Two of the clusters differentiated into a group showing a correlation between the percentage of neutrophils and disease activity progression and a group showing a correlation between the percentage of lymphocytes and disease activity progression. The third cluster, in which the percentage of neutrophils correlated to a lesser degree with disease activity, was functionally more heterogeneous. Patients in the neutrophil-driven clusters had an increased risk of developing proliferative nephritis.

CONCLUSION

Our findings indicate that SLE patients can be stratified into 3 subgroups of patients who show different mechanisms of disease progression and are clinically differentiated. Our results have important implications for treatment options, the design of clinical trials, our understanding of the etiology of the disease, and the prediction of severe glomerulonephritis.