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PubMed2004

Rheumatoid arthritis specific anti-Sa antibodies target citrullinated vimentin.

Antibodies directed to the Sa antigen are highly specific for rheumatoid arthritis (RA) and can be detected in approximately 40% of RA sera. The antigen, a doublet of protein bands of about 50 kDa, is present in placenta and in RA synovial tissue. Although it has been stated that the Sa antigen is citrullinated vimentin, experimental proof for this claim has never been published. In this study, we investigated the precise nature of the antigen. Peptide sequences that were obtained from highly purified Sa antigen were unique to vimentin. Recombinant vimentin, however, was not recognized by anti-Sa reference sera. In vivo, vimentin is subjected to various post-translational modifications, including citrullination. Since antibodies to citrullinated proteins are known to be highly specific for RA, we investigated whether Sa is citrullinated and found that Sa indeed is citrullinated vimentin. Anti-Sa antibodies thus belong to the family of anticitrullinated protein/peptide antibodies. The presence of the Sa antigen in RA synovial tissue, and the recent observation that vimentin is citrullinated in dying human macrophages, make citrullinated vimentin an interesting candidate autoantigen in RA and may provide new insights into the potential role of citrullinated synovial antigens and the antibodies directed to them in the pathophysiology of RA.

Antibodies, Anti-Idiotypic↗
PubMed1993

Inhibition by methylene blue of the L-arginine metabolism to L-citrulline coupled with nitric oxide synthesis in cultured endothelial cells.

The effect of methylene blue on the metabolism of L-arginine to L-citrulline coupled with nitric oxide synthesis in cultured endothelial cells was investigated. The addition of the calcium ionophore ionomycin (10(-8)-10(-5) M) to endothelial cells stimulated L-citrulline formation from L-arginine. Ionomycin-stimulated L-citrulline formation was inhibited by NG-nitro-L-arginine (10(-6)-10(-4) M), a potent inhibitor of nitric oxide synthase. These results indicate that ionomycin-stimulated L-citrulline formation was coupled to nitric oxide synthesis. Therefore, L-citrulline formation from L-arginine was used as a marker for nitric oxide synthesis. Methylene blue (10(-4)-10(-3) M) inhibited ionomycin-stimulated L-citrulline formation in bovine aortic endothelial cells. Moreover, the formation of L-citrulline by the particulate fraction obtained from bovine cultured endothelial cells was also inhibited by methylene blue concentrations in excess of 10(-5) M. Although the addition of methylene blue to various tissues has been reported to release superoxide anions (Wolin et al., 1990; Marczin et al., 1992), inhibition of L-citrulline formation by methylene blue was not affected by the presence of superoxide dismutase (100 micrograms/mL) in either cultured endothelial cells or the particulate fraction. These findings suggest that methylene blue is a direct inhibitor of nitric oxide synthase in bovine aortic endothelial cells.

Amino Acid Oxidoreductases↗
PubMed1995

Arginine synthesis from citrulline in perivascular nerves of cerebral artery.

Cerebral neurogenic vasodilation is mediated predominantly by nitric oxide (NO). Thus, NO was suggested to be a vasodilator transmitter. In the present study, the possibility that cerebral perivascular nerves can convert citrulline to arginine was examined to ascertain that NO is derived directly from these perivascular nerves. To investigate the uptake of citrulline and its conversion to arginine, both fresh and cold storage-denervated porcine cerebral arteries with or without endothelial cells were incubated at 37 degrees C for 2 hr in Krebs-Ringer bicarbonate buffer containing 0.5 mM purified [14C]ureido-citrulline. The formation of [14C]arginine was measured as 14CO2 by a coupled enzymatic assay involving arginase and urease. The abolishment of nitric oxidergic nerves was verified by NADPH-diaphorase (constitutive NO synthases) histochemical staining method. The results indicated that there was an active conversion of [14C]arginine from [14C]citrulline in nerve-intact arteries denuded of endothelial cells. The conversion was significantly decreased in denervated arteries, accompanied by a significantly reduced citrulline uptake into these denervated arteries. L-Glutamine, but not L-glutamate, gamma-aminobutyric acid, or nitro-L-arginine significantly inhibited the uptake of [14C]citrulline into cerebral perivascular nerves. These data suggest that porcine cerebral vasodilator nerves are nitric oxidergic in nature and citrulline, co-produced with NO by NO synthases from arginine, can be recycled to form arginine in these nerves. The existence of a functional arginine-citrulline cycle may contribute to a constant supply of L-arginine and suggests a neuronal source of NO for inducing cerebral vasodilation.

Animals↗
PubMed2006

Association of citrullinated proteins with synovial exosomes.

OBJECTIVE: In addition to releasing proteins and mediators, cells also release membrane vesicles (exosomes and apoptotic blebs) into the extracellular environment. Apoptotic blebs contain multiple autoantigens, but few data are available concerning the protein content of exosomes. Exosomes are formed during an immune response and can directly stimulate T cells or bind to dendritic cells. The aim of this study was to identify the nature of synovial exosomes from patients with different rheumatic diseases and to examine their potential autoantigenic content, which may be involved in the induction of an autoimmune response. METHODS: Synovial exosomes from patients with rheumatoid arthritis (RA), patients with reactive arthritis, and patients with osteoarthritis were purified, analyzed by electron microscopy, and labeled with immunogold to detect IgG and IgM molecules. Autoantigen content was identified by 2-dimensional electrophoresis-immunoblotting and subsequent mass spectrometry. In order to investigate the presence of citrullinated proteins, immunoblotting with anticitrulline antibodies was performed. RESULTS: Citrullinated proteins were observed in all exosome preparations, in contrast to other autoantigenic proteins (e.g., BiP and heterogeneous nuclear RNP A2) that were previously observed in RA and other autoimmune diseases. These citrullinated proteins included the fibrin alpha-chain fragment, fibrin beta-chain, fibrinogen beta-chain precursor, fibrinogen D fragment, and the Sp alpha (CD5 antigen-like protein) receptor. Purification of synovial exosomes led to the detection of citrullinated fibrinogen and citrullinated Sp alpha associated with IgM and IgG. CONCLUSION: Synovial exosomes contain citrullinated proteins, which are known to be autoantigens in RA. Although immune mechanisms in which exosomes carry citrullinated peptides could play an important role in the induction and distribution of citrullinated proteins, there must be a specific recognition of these proteins that is unique to the RA immune system.

Arthritis↗
PubMed2006

Deiminated Epstein-Barr virus nuclear antigen 1 is a target of anti-citrullinated protein antibodies in rheumatoid arthritis.

OBJECTIVE: To test the hypothesis that deimination of viral sequences containing Arg-Gly repeats could generate epitopes recognized by anti-citrullinated protein antibodies (ACPAs) that are present in rheumatoid arthritis (RA) sera. METHODS: Multiple antigen peptides derived from Epstein-Barr virus (EBV)-encoded Epstein-Barr nuclear antigen 1 (EBNA-1) were synthesized, substituting the arginines with citrulline, and were used to screen RA sera. Anti-cyclic citrullinated peptide antibodies were purified by affinity chromatography and tested on a panel of in vitro deiminated proteins. Their ability to bind in vivo deiminated proteins was evaluated by immunoprecipitation, using EBV-infected cell lines. RESULTS: Antibodies specific for a peptide corresponding to the EBNA-1(35-58) sequence containing citrulline in place of arginine (viral citrullinated peptide [VCP]) were detected in 50% of RA sera and in <5% of normal and disease control sera. In addition, affinity-purified anti-VCP antibodies from RA sera reacted with filaggrin-derived citrullinated peptides, with deiminated fibrinogen, and with deiminated recombinant EBNA-1. Moreover, anti-VCP antibodies immunoprecipitated, from the lysate of calcium ionophore-stimulated lymphoblastoid cell lines, an 80-kd band that was reactive with a monoclonal anti-EBNA-1 antibody and with anti-modified citrulline antibodies. CONCLUSION: These data indicate that ACPAs react with a viral deiminated protein and suggest that EBV infection may play a role in the induction of these RA-specific antibodies.

Adult↗
PubMed2005

Expression of citrullinated proteins in murine experimental autoimmune encephalomyelitis.

In this study, we demonstrate for the first time the immunohistochemical expression of citrullinated proteins in the central nervous system (CNS) of mice with myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE). By using an established monoclonal antibody (F95) against natural and synthetic citrullinated proteins (Nicholas and Whitaker [2002] Glia 37:328-336), numerous, small, previously unrecognized "patches" of citrullinated proteins were discovered throughout EAE brains, whereas EAE spinal cords showed similar but much larger lesions. On dual color immunofluorescence, these lesions were found to contain citrullinated myelin basic protein (MBP) and were surrounded by astrocytes immunoreactive for both glial fibrillary acidic protein (GFAP) and F95. These lesions became evident about the time when EAE mice became symptomatic and increased in size and number with increasing disease severity. In some sections of spinal cord but not brains of severely debilitated EAE mice, a widespread gliotic response was seen, with astrocytes containing citrullinated GFAP spread throughout the gray and white matter. Western blot analysis of acidic proteins from the brains and spinal cords of EAE mice had higher levels of multiple citrullinated GFAP isoforms compared with controls, with more F95-positive bands in the EAE brains vs. spinal cords. These results raise the possibility that citrullination of both GFAP and MBP may contribute to the pathophysiology of EAE and that the brains of EAE mice may contain more pathology than previously realized.

Animals↗
PubMed1997

Citrulline-argininosuccinate-arginine cycle coupled to Ca2+-signaling in rat pancreatic beta-cells.

Pancreatic beta-cells possess nitric oxide (NO) synthases (NOSs) which synthesize NO and L-citrulline from L-arginine. The present study was designed to explore the mechanism of citrulline and arginine metabolism in beta-cells and its possible coupling to beta-cell functions. The enzymes involved in citrulline-arginine metabolism, argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), and NOS were expressed in rat islets and insulinoma HIT T15 cells. In the presence of stimulatory glucose, L-citrulline and L-argininosuccinate at physiological concentrations (0.1-1 mM) increased cytosolic Ca2+ concentration ([Ca2+]i) in rat beta-cells. The citrulline-induced [Ca2+]i increase was inhibited by a NOS inhibitor, N(G)-monomethyl-L-arginine (NMMA). L-citrulline also stimulated NO production in HIT cells, which was inhibited by NMMA. In conclusion, L-citrulline is metabolized by ASS-ASL-NOS cycle to produce NO, which in turn increases [Ca2+]i in beta-cells.

Animals↗
PubMed1991

On leaking into the lumen, amino acids cross the tubule cells. Secretion of L-citrulline in the isolated-perfused non-filtering kidney of the African clawed toad (Xenopus laevis).

In our previous studies we were able to show that L-citrulline is taken up across the contraluminal membrane into the tubule cells of the isolated perfused non-filtering kidney of the African clawed toad (Xenopus laevis). We have also described the tubular metabolism of the L-citrulline taken up. The remaining question was whether peritubular L-citrulline gains access to the tubular lumen and, if so, by what kind of mechanism. The method was the same as that described in our previous study: the perfusion of the kidneys was performed through both portal veins (2 ml/h into each) with a solution containing inulin. In order to stimulate the urine formation in the non-filtering kidney, we added p-aminohippurate to the perfusion solution. In the urine collected from the ureters no inulin could be detected. Thus, the glomeruli were not reached by the perfusate, and no glomerular filtration took place. Upon adding 65 mumol/l L-citrulline to the perfusion solution (corresponding to the physiological plasma concentration), a urinary excretion rate of this amino acid of 4.5 +/- 0.4 nmol.h-1.g-1 (n = 6) was determined. During perfusion under the same conditions with D-citrulline (65 mumol/l) the excretion rate was only 0.36 +/- 0.1 nmol.h-1.g-1 (n = 5). A similarly low excretion rate was also found with L-citrulline when L-phenylalanine (20 mmol/l) was added to the perfusate or when NaCl was substituted by mannitol. These data show that L-citrulline taken up from the contraluminal side of the renal tubular epithelium enters the tubular lumen to a much greater extent than its D-isomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1975

Citrulline metabolism in normal and citrullinemic human lymphocyte lines.

Citrullinemia is one of the five aminoacidurias associated with the Krebs-Henseleit urea cycle. A long-term lymphocyte line (UM-21) derived from a patient with this disease and nine of ten clones of this line were found to have no activity for the enzyme argininosuccinate synthetase (AS), as demonstrated by their inability to grow in medium in which citrulline had been substituted for arginine, by their inability to incorporate arginine-C14 derived from citrulline-C14 into cellular protein, and by direct enzyme assay. One clone had normal or nearly normal argininosuccinate synthetase activity, as demonstrated by the same criteria. Nutritional "variants" able to grow logarithmically in medium containing citrulline were isolated from UM-21 and three clones. The apparent Kms of AS for citrulline in UM-21, the ten clones, the variant lines, and a normal line were measured and fell into three groups: AS in UM-21 and nine clones had no measurable apparent Km for citrulline; AS in the variant cells had apparent Kms for citrulline of approximately 20 mM; and AS in the normal cell line and one clone had apparent Kms for citrulline of 0.2 mM. The data suggest that the defect in the citrullinemic cell lines is due to a mutation in the structural gene coding for argininosuccinate synthetase.

Amino Acid Metabolism, Inborn Errors↗
PubMed1990

The preparation of antibodies reactive against citrulline-containing charge isomers of myelin basic protein but not against the arginine-containing charge isomers.

Human myelin basic protein (MBP) is composed of several charge isomers, the result of various post-translational modifications. One of the charge isomers C-8, has been shown in our laboratory to contain six citrullinyl residues which replace arginyl residues at selected sites in the MBP. In order to determine the disposition of the citrulline-containing charge isomers in the myelin stack, we prepared specific antisera against the citrullinyl group. Since 9-fluorenylmethoxycarbonyl (Fmoc)-citrulline, required for the preparation of the synthetic peptides to be used for antibody production, was not commercially available, synthesis of the Fmoc-citrulline was a necessary prerequisite. The synthesis and purification of the N-9-fluorenylmethyloxycarbonyl derivative of citrulline is described. It was characterized by thin layer chromatography, 1H and 13C NMR spectroscopy, fast-atom bombardment mass spectroscopy, and thermal analyses. It was used in the automated peptide synthesis of a peptide Ala-Cit-His-Gly-Phe-Leu-Pro-Cit-His-Arg corresponding to residues 24-33 and Gly-Cit-Asp-Ser-Arg-Ser-Gly-Ser-Pro-Met-Ala-Cit-Arg, corresponding to residues 158-170 of the C-8 sequence, a naturally occurring charge isomer of human myelin basic protein, and a tetracitrulline peptide, Cit-Cit-Cit-Cit-Gly. The tetracitrulline peptide was used for the production of an antibody shown to react only with synthetic peptides and proteins containing citrulline. This antibody was used to distinguish between a citrulline-containing protein, C-8, a naturally occurring charge isomer of MBP, and a non-citrulline-containing charge isomer of MBP, C-1.

Amino Acid Sequence↗
PubMed1992

Nitric oxide synthase from cerebellum catalyzes the formation of equimolar quantities of nitric oxide and citrulline from L-arginine.

This study examined whether constitutive nitric oxide (NO) synthase from rat cerebellum catalyzes the formation of equimolar amounts of NO plus citrulline from L-arginine under various conditions. Citrulline was determined by monitoring the formation of 3H-citrulline from 3H-L-arginine. NO was determined by monitoring the formation of total NOx (NO+nitrite [NO2-] + nitrate [NO3-]) by chemiluminescence after reduction of NOx to NO by acidic vanadium (III). Equal quantities of NO plus citrulline were generated from L-arginine and the formation of both products was linear for about 20 min at 37 degrees C provided L-arginine was present in excess to maintain a zero order reaction rate. Deletion of NADPH, addition of the calmodulin antagonist calmidazolium, or addition of NO synthase inhibitors (NG-methyl-L-arginine, NG-amino-L-arginine) abolished or markedly inhibited the formation of both NO and citrulline. The Km for L-arginine (14 microM; 18 microM) and the Vmax of the reaction (0.74 nmol/min/mg protein; 0.67 nmol/min/mg protein) were the same whether NO or citrulline formation, respectively, was monitored. These observations indicate clearly that NO and citrulline are formed in equimolar quantities from L-arginine by the constitutive isoform of NO synthase from rat cerebellum.

Amino Acid Oxidoreductases↗
PubMed1991

Citrulline in the rat brain: immunohistochemistry and coexistence with NADPH-diaphorase.

The presence in the brain of the urea cycle intermediate citrulline in the absence of a complete urea cycle has never been adequately explained. In an attempt to clarify this problem, we developed antibodies to citrulline and determined the distribution of citrulline-immunoreactivity in fixed sections of rat brain using immunoperoxidase and indirect immunofluorescence techniques. Citrulline-positive neurons were found to have a restricted distribution within the brain. A few cells were present in the cortex and corpus callosum. A large population of strongly stained cells was diffusely scattered throughout the striatum, nucleus accumbens and olfactory tubercle. Less strongly stained cells were detected in the supraoptic and paraventricular nuclei of the hypothalamus, the dorsal raphe, and the laterodorsal and pedunculopontine tegmental nuclei of the pons. The citrulline-immunoreactive cells were similar to those previously shown to contain NADPH-diaphorase activity, and double staining experiments indicated that citrulline-immunoreactivity was present in a subpopulation of NADPH-diaphorase-positive neurons. We have recently identified NADPH-diaphorase as a nitric oxide synthase. Thus the presence of citrulline in these cells suggests that it is formed within the brain as a coproduct during nitric oxide formation from arginine.

Amino Acid Oxidoreductases↗
PubMed1990

Effect of ornithine concentration on citrulline synthesis in mouse liver mitochondria.

The rate of citrulline synthesis in mitochondria from OTC-deficient spf-ash mice (15% of the normal activity) was found to be the same as that in mitochondria from control mice. The amount of NAG in their mitochondria varied markedly according to whether they had received a high- or low-protein diet, and the rate of citrulline synthesis was found to be affected by the level of NAG. These results indicate that the CPS stage, not the OTC stage, is rate-limiting in the citrulline synthesis process. Kinetic studies on the effect of ornithine concentration on citrulline synthesis in mitochondria showed that the Km for ornithine was very low in the mitochondria from the mice given a low-protein diet. Kinetic studies on the effect of ornithine concentration on mouse OTC at various concentrations of carbamylphosphate showed that OTC has a ping-pong mechanism, i.e., that the Km for ornithine and Vmax decrease with the reduction in carbamylphosphate concentration. This may explain the low Km value observed in citrulline synthesis in the mitochondria. We conclude that in mitochondrial citrulline synthesis the rate of carbamylphosphate synthesis by CPS in the presence of NAG plays a key role in determining the rate of citrulline synthesis and ornithine dependency.

Animals↗
PubMed2004

Plasma citrulline concentration: a surrogate end point for radiation-induced mucosal atrophy of the small bowel. A feasibility study in 23 patients.

PURPOSE: Plasma citrulline, a nitrogen end product of glutamine metabolism in small-bowel enterocytes, was suggested as a marker of radiation-induced small-bowel epithelial cell loss in mice after single-dose whole-body irradiation. Our objective was to evaluate the feasibility of citrulline as a marker for radiation-induced small-intestinal mucosal atrophy in patients during and after abdominal fractionated radiotherapy. METHODS AND MATERIALS: Twenty-three patients were studied weekly during treatment and at intervals of 2 weeks and 3 and 6 months after treatment by postabsorptive plasma citrulline concentration and clinical toxicity grading. The interrelationship between these variables and the correlation with small-bowel dose and volume parameters were investigated. RESULTS: During fractionated radiotherapy, citrulline concentration significantly decreased as a function of the radiation dose (p < 0.001) and the volume of small bowel treated (p = 0.001). The plasma citrulline concentration correlated with clinical toxicity during the last 3 weeks of treatment. As a whole, citrulline concentration correlated better with radiation dose and volume parameters than clinical toxicity grading. CONCLUSIONS: In patients treated with fractionated radiation therapy for abdominal or pelvic cancer sites, plasma citrulline concentration may be a simple objective marker for monitoring epithelial cell loss, a major event in acute radiation-induced small-bowel toxicity.

Adult↗
PubMed2005

Serum citrulline is a simple quantitative marker for small intestinal enterocytes mass and absorption function in short bowel patients.

BACKGROUND: To investigate the clinical significance of serum citrulline in evaluating the remnant small bowel enterocytes mass and absorptive function in short bowel (SB) patients. MATERIALS AND METHODS: Serum citrulline concentrations were determined using high-performance liquid chromatography (HPLC) in 22 SBS patients and 33 healthy controls. Five-hour urine D-xylose excretion and digestive protein absorption were measured using HPLC and micro-Kjeldahl method, respectively. Small bowel length and surface area were assessed on X-ray radiograph. Correlations between serum citrulline levels and small bowel length, small bowel surface, and nutritional substrate digestive absorption percentage were analyzed. For six patients receiving bowel rehabilitation therapy, serum citrulline, D-xylose excretion, and intestinal protein absorption were measured pre- and immediately postmanagement, and their correlations were analyzed. RESULTS: Serum citrulline levels were significantly lower in SB patients compared with healthy controls. In SB patients, they correlated well with remnant small bowel length (r = 0.82, P < 0.001), surface area (r = 0.86, P < 0.001), 5-h urine D-xylose excretion (r = 0.56, P = 0.007), and digestive protein absorption (r = 0.48, P = 0.046). The increased percentage of serum citrulline level in six patients receiving rehabilitation therapy followed a trend of correlating with that of intestinal protein absorption (r = 0.79, P = 0.063) and urine D-xylose excretion (r = 0.81, P = 0.053). CONCLUSIONS: In patients with short bowel syndrome, serum citrulline is a simple and accurate biomarker for the severity of intestinal failure and may be a candidate marker for the gut-trophic effects of bowel rehabilitation therapies.

Absorption↗
PubMedDate not supplied

An association of lower serum citrulline levels within 30 days of acute rejection in patients following small intestine transplantation.

INTRODUCTION: In a prospective protocol we studied whether serum citrulline level within 30 days of an acute rejection was predictive of the episode. METHODS: An acute rejection episode was defined as the date of occurrence of any biopsy-proven rejection in which treatment was initiated until two successive biopsies showed no further rejection. We compared the mean citrulline level based on values determined within 30 days of the start of an acute rejection episode with the mean citrulline level measured on the same patient during a rejection-free period. Serum citrulline measurements were available immediately prior to the occurrence of rejection for 22 patients who experienced 37 episodes. RESULTS: For the 12 episodes of mild rejection, the mean serum citrulline level +/- SE (standard error) was 15.0 + 2.3 micromol/L prior to rejection and 18.8 +/- 2.4 micromol/L during the rejection-free periods. A paired t test of the mean differences was not significant (P = 17). For the 25 episodes of moderate or severe rejection, the mean serum citrulline level was 12.4 +/- 1.1 micromol/L before rejection and 18.8 +/- 2.0 micromol/L during the rejection-free periods. A paired t test of the mean difference was statistically significant (P = .002). CONCLUSIONS: Although further study of citrulline as a marker for the early detection of acute rejection episodes is needed, our hope is that its use will help to prevent some of these early episodes from evolving into full-blown moderate or severe grades of rejection.

Acute Disease↗
PubMed1999

Expression of citrulline-nitric oxide cycle in lipopolysaccharide and cytokine-stimulated rat astroglioma C6 cells.

Nitric oxide (NO) is involved in many physiological and pathological processes in the brain. NO is synthesized from arginine by nitric oxide synthase (NOS), with citrulline generated as a by-product of the reaction. Thus, citrulline can by recycled to arginine by argininosuccinate synthetase (AS) and argininosuccinate lyase (AL) via the citrulline-NO cycle. Rat astroglioma C6 cells were treated with bacterial lipopolysaccharide (LPS), interferon-gamma (IFNgamma) and tumor necrosis factor-alpha, and the expression of the enzymes of the citrulline-NO cycle was investigated by RNA blot and immunoblot analyses. NO production from arginine and citrulline was also assessed. iNOS mRNA and protein were induced 6-12 h after stimulation with LPS and cytokines and decreased at 24 h. AS mRNA increased up to 12 h and decreased at 24 h. AS protein increased gradually up to 48 h. On the other hand, AL mRNA remained unchanged by stimulation. NO production from arginine was enhanced by the treatment with LPS and cytokines. NO production was also observed when arginine was replaced by citrulline. These results indicate that NO production is enhanced in LPS- and cytokine-stimulated C6 cells due to induction of iNOS and that the citrulline-arginine recycling is important for NO production.

Animals↗
PubMed2001

IgG reactivity against citrullinated myelin basic protein in multiple sclerosis.

An increased level of citrullinated myelin basic protein (MBP-C8) has been reported in the brains of multiple sclerosis (MS) patients. However, the involvement of the immune response to post-translational modified MBP in the pathophysiology of MS remains speculative. The aim of this study was to compare the levels of immunoglobulin G antibodies to several MBP epitopes, before and after citrullination, in the cerebrospinal fluid (CSF) and sera of MS patients using enzyme-linked immunosorbent assay (ELISA). We analyzed antibody reactivity against various MBP-peptides in the CSF and sera of 60 MS patients, and 30 patients with other neurological diseases (OND) as controls. The peptides tested were: MBP(75-98) (peptide 1), native (peptide 2) and citrullinated (peptide 3) MBP(108-126) (ARG(122)-->Cit(122)), and native (peptide 4) and citrullinated (peptide 5) MBP(151-170) (ARG(159, 170)-->Cit(159, 170)). All selected peptides could support an immune reactivity in CSF and sera of MS and OND patients. A higher reactivity against peptide 4 was found in the CSF of MS patients compared with OND patients (P<0.0001), but not against citrullinated peptides (peptides 3 and 5). However, we observed that the citrullination state of peptide 2 modified the patterns of immune reactivity more markedly in MS patients (P<0.0001) than in OND patients (P<0.02). Although some MBP epitopes could be a potential target in MS, our data did not demonstrate any difference of antibody response to MBP peptides in their citrullinated forms.

Adolescent↗