MESSA A PUNTO DI UN METODO PER LA VALUTAZIONE DI ANTICORPI ANTI-NR2 PER LO STUDIO DELLA LORO ASSOCIAZIONE CON DISTURBI COGNITIVI SU BASE AUTOIMMUNE

Cognitive impairment is a worrying problem in aging, and it is a common cause of disability, with considerable social, economical and health costs. Frequently it is not a consequence of pathological events, like stroke, ischemic lesions, head injury, infections etc… but the mechanisms are unknown. Some pathologies, like Systemic Lupus Erithematosus (SLE) and Antiphospholipid Syndrome (APS) may contribute to the onset of cognitive impairment. SLE and APS patients display an increased risk of developing cognitive impairment as a consequence of central nervous system (CNS) involvement, mediated by vasculopathy of intracranial vessels, local or systemic production of inflammatory mediators and generation of specific autoantibodies (autoAbs). Recently a subset of anti-dsDNA autoAbs, cross-reacting with the NMDA glutamate receptor subunit NR2, has been detected in SLE patients. There is also evidence from in vitro experiments and in murine models that these autoAbs may be responsible for cognitive impairement. However a clear clinical association between these autoAbs and cognitive defects is still matter of debate in human studies. Lack of standardization in both the classification of neuropsychiatric (NP) events and the methodology used for autoAbs detection are likely the causes for the contrasting results reported in literature. Anti-NR2 autoAbs are reported with a prevalence of 30% in SLE, instead no data are available on the occurrence of these autoAbs in primary APS (PAPS). The aims of this study were i) to compare the sensitivity/specificity of different techniques for anti-NR2 titration, ii) to investigate whether anti-NR2 autoAbs can be detectable in PAPS and iii) to evaluate the incidence of cognitive impairment in LES and PAPS patients, iv) to evaluate whether the presence of anti-NR2 Abs could be potentially able to predict the appearance of NP manifestations in these patients. We performed two different immunoenzymatic assays for anti-NR2 autoAbs detection using two different antigenic forms of NR2, a decapeptide and a branched peptide. The cut-off, the sensibility and the sensitivity of both tests were calculated. We enrolled 20 SLE and 33 PAPS patients with or without CNS involvement and they were tested for anti-NR2, as well as for ANA, ENA, anti-nucleosome (anti-NCS), LAC, anti-CL, and anti-b2GPI Abs. Among patients, 19 SLE and 15 PAPS underwent an extensive neuropsychological and psycodiagnostic assessment. Attention, executive functions, language, memory, visuo-spatial pianification, praxis and visual discrimination were investigated. Psychological status was assessed with Symptom Checklist, Beck Depression Inventory, State-Trait Anxiety Inventory-Y and Short-Form Health Survey-36. The two different assays for anti-NR2 detection showed high heterogeneity in terms of specificity, ranged from 70% in decapeptide ELISA to 89% in branched peptide ELISA, respectively. The assay sensitivity was statistically comparable, with a percentage of positive SLE sera near to the expected 30% in both decapeptide and branched peptide ELISA. In PAPS the prevalence of Anti-NR2 autoAbs varied from 61% to 24% when the decapeptide or branched peptide were used as antigenic target, but in both cases no association with CNS involvement was found. 67% and 80% of PAPS sera with high anti-B2GPI activity were negative for anti-NR2 using as antigen decapeptide or branched peptide, respectively, suggesting that there is not any association between these antibodies (Rj = 0,05; Rj = 0,14) and a cross-reactivity is unlikely. About association between anti-NR2 and anti-NCS autoAbs, only 25% PAPS sera with medium/high titer of anti-NCS were negative for anti-NR2 (Rj = 0,44) using decapeptide. The percentage increases to 50% with branched peptide (Rj 0,044). These differences might be due to a higher stickiness of the decapeptide. Qualitative and quantitative differences were detected in neuropsychological profiles between APS and SLE patients: SLE patients had significantly bad performance in calculation, executive functions, frontal inhibition, visuospatial planning, memory; 80% PAPS had at least a cognitive impairment and they had significantly bad performance in lexical evocation, visual discrimination. Moreover, psychoemotional tests revealed that PAPS patients show more frequently anxiety, while SLE patients are more prone to depression. Positive and negative correlations were found between anti-dsDNA, anti-CL or anti-b2GPI and different neuropsicological and psychoemotional tests. Our results suggest that anti-NR2 assay using branched peptide as antigen seems to be more specific than the one using decapeptide. As different techniques give different results more set up experiments are needed in order to select the best assay for anti-NR2 autoAbs detection. Anti-NR2 Abs may be found both in SLE and PAPS. This finding is in line with the fact that several autoAbs against nuclear antigens can be found in PAPS making the two diseases close each other. Neuropsychological profiles demonstrate that SLE and PAPS patients both present a mild cognitive impairment, that could have a significant influence on patient’s lifestyle. So SLE and PAPS patients could be at risk of developing dementia. A not clear association between anti-NMDA Abs and cognitive impairment was observed. Probably Abs couldn’t pass the emato-encephalic barrier and damage brain cells or the tests could have been performed in a remissive phase of the cognitive damage.