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<p>Neuropsychiatric symptoms in systemic lupus erythematosus (SLE) are not uncommon, yet the mechanisms underlying disease initiation and progression in the brain are incompletely understood. Although the role of T cells in other lupus target organs such as the kidney is well defined, which T cells contribute to the pathogenesis of neuropsychiatric SLE is not known. The present study was aimed at characterizing the CD4 T cell populations that are present in the choroid plexus (CP) of MRL/MpJ-faslpr mice, the primary site of brain infiltration in this classic lupus mouse model which exhibits a prominent neurobehavioral phenotype. T cells infiltrating the CP of MRL/MpJ-faslpr mice were characterized and subset identification was done by multiparameter flow cytometry. We found that the infiltrating CD4 T cells are activated and have an effector phenotype. Importantly, CD4 T cells have a T follicular helper cell (T_FH) like phenotype, as evidenced by their surface markers and signature cytokine, IL-21. In addition, CD4 T_FH cells also secrete significant levels of IFN-γ and express Bcl-6, thereby conforming to a potentially pathogenic T helper population that can drive the disease progression. Interestingly, the regulatory axis comprising CD4 T regulatory cells is diminished. These results suggest that accumulation of CD4 T_FH in the brain of MRL/MpJ-faslpr mice may contribute to the neuropsychiatric manifestations of SLE, and point to this T cell subset as a possible novel therapeutic candidate.</p

Lipid profiles and methyl group donors in SLE.

<p>Plotted in the heatmap in (A) are the serum levels of long chain fatty acids (FA) and medium chain FA in 9 healthy controls and 20 SLE subjects, as determined by the metabolomic scan. Presentation details are as in Fig. 1(I). In the metabolomic scan, additional differences were noted in the serum levels of 9-HODE and 13-HODE (C), methionine (F), cysteine (G), choline (H) and vitamin B6 (I); presentation details are as in Fig. 1. In (C) and (I), the SLE patients have been segregated into 2 groups - mild SLE (SLEDAI <6; N = 10) and active SLE (SLEDAI >5; N = 10). Also plotted are validation assays for serum levels of free fatty acids (FFA; B), the lipid peroxidation marker, MDA (D), glutathione (GSH; E), and vitamin B6 (J), ascertained in an independent cohort of 38 SLE patients and 14 healthy controls, using commercially available assays, independent of the original metabolomic scan. Each dot represents data from an individual subject (*,P<0.05; **,P<0.01; ***,P<0.001).</p

Demographics and Clinical characteristics of SLE patients used for the metabolomic profiling.

<p>Demographics and Clinical characteristics of SLE patients used for the metabolomic profiling.</p

An overview of the metabolic imbalances in SLE.

<p>The most significant metabolic alterations in SLE have been organized into different biochemical pathways, including glycolysis (A), Krebs cycle (B), fatty acid oxidation (C), amino acid pools (D), lipid biosynthesis (E), essential FA (F), eicosanoid biosynthesis (G) and methyl group interchange pathways (H) leading to glutathione generation (I). Metabolites that were elevated in SLE are in red font, while reduced metabolites are in green font. Mitochondrial events are blue-boxed, while events that take place in the endoplasmic reticulum are yellow-boxed. Salient metabolic consequences that can potentially contribute to the manifestations of SLE are highlighted in pink.</p

Key metabolic imbalances in SLE affecting carbohydrate, lipid or amino acid metabolism.

<p>The sera of 20 SLE patients and 9 healthy controls were comprehensively scanned for differences in small molecules using LC/MS and GC/MS platforms, referred to as the “metabolomic scan”. Shown are the mean metabolite levels of 3 glycolytic intermediates (A–C), three Kreb’s cycle intermediates (D–F), and two products of fatty acid β-oxidation (G–H). Open bars = healthy controls; closed bars = SLE patients. (*,P<0.05; **,P<0.01; ***,P<0.001). Plotted in (I) is a heatmap of serum amino acid levels in healthy subjects (first 9 columns) versus SLE patients (rightmost 20 columns), as determined by the metabolomic scan described above. Red = elevated; green = reduced, relative to the mean levels of the metabolite within the 29 study subjects. The actual mean levels of the metabolites are listed in Supplementary <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037210#pone.0037210.s002" target="_blank">Table S1</a>.</p

Correlation between serum IGFBP-4 levels and clinical parameters.

<p>Serum IGFBP-4 levels were plotted against severity of proteinuria, as measured by spot urinary protein:creatinine ratio (<b>A</b>), serum creatinine (<b>B</b>), eGFR (as calculated using the MDRD study equation (<b>C</b>), and systemic lupus erythematosus disease activity index (SLEDAI, <b>D</b>), respectively. Also plotted are the corresponding <i>R</i> and <i>P</i> values. eGFR, estimated glomerular filtration rate.</p

Insulin-Like Growth Factor Binding Protein-4 as a Marker of Chronic Lupus Nephritis - Fig 4

<p>Plotted in <b>(A)</b> are urine protein creatinine ratios (UPCR) versus serum IGFBP4 levels in the CKD control subjects. Plotted in <b>(B)</b> are the serum beta-2-microglobulin levels, as assessed by ELISA, in lupus nephritis patients, healthy controls and CKD controls. Other details are as listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151491#pone.0151491.g001" target="_blank">Fig 1</a> legend.</p

Correlation between serum IGFBP-4 levels with renal pathology.

<p>Serum IGFBP-4 levels in 18 patients with proliferative (ISN/RPS class III and class IV) LN whose blood samples were obtained at the time of renal biopsy were correlated with the activity index (<b>A</b>) and chronicity index (<b>B</b>) of renal pathology, as detailed in methods. Also depicted are correlations of eGFR with chronicity index (<b>C</b>). eGFR, estimated glomerular filtration rate.</p

Serum IGFBP-4 levels were elevated in patients with lupus nephritis.

<p>Serum 86 patients with LN, 23 healthy controls, 20 patients with CKD and 15 patients with RA were assayed for serum IGFBP-4 levels by ELISA. Plotted in <b>(A)</b> are serum levels of IGFBP-4 in the 3 groups, indicating significantly higher levels in LN as compared to the CKD, RA and healthy controls (<i>P</i> < 0.01 and <i>P</i> < 0.0001, respectively). Receiver operating characteristic curves were generated using serum IGFBP-4 levels measured by ELISA <b>(B)</b>. Also indicated are the corresponding AUC values. Plotted in <b>(C)</b> are serum IGFBP-4 levels in two groups of patients with LN, those with active LN (rSLEDAI > 0) and those with non-active LN (rSLEDAI = 0), <i>P</i> > 0.3. <b>D</b>: serum IGFBP-4 levels in patients with LN of different ISN/RPS classes, whose blood samples were obtained within 5 months of renal biopsy. No statistical significance were found among the patients with LN of classes II (n = 4), III (n = 9), IV (n = 19), and V (n = 8), <i>P</i> > 0.05.</p

Characteristics of Controls used for validation studies.

<p>Characteristics of Controls used for validation studies.</p