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Longitudinal mapping of antibody-based SARS-CoV-2 immunity is critical for public health control of the pandemic and vaccine development. We performed a longitudinal analysis of the antibody-based immune response in a cohort of 100 COVID-19 individuals who were infected during the first wave of infection in northern Italy. The SARS-CoV-2 humoral response was tested using the COVID-SeroIndex, Kantaro Quantitative SARS-CoV-2 IgG Antibody RUO Kit (R&D Systems, Bio-Techne, Minneapolis, USA) and pseudotype-based neutralizing antibody assay. Using sequential serum samples collected from 100 COVID-19 recovered individuals from northern Italy—mostly with mild disease—at 2 and 10 months after their first positive PCR test, we show that 93% of them seroconverted at 2 months, with a geometric mean (GeoMean) half-maximal neutralization titer (NT50) of 387.9. Among the 35 unvaccinated subjects retested at 10 months, 7 resulted seronegative, with an 80% drop in seropositivity, while 28 showed decreased anti-receptor binding domain (RBD) and anti-spike (S) IgG titers, with a GeoMean NT50 neutralization titer dropping to 163.5. As an NT50 > 100 is known to confer protection from SARS-CoV-2 re-infection, our data show that the neutralizing activity elicited by the natural infection has lasted for at least 10 months in a large fraction of subjects.

Summary Nuclear interferon-inducible protein 16 (IFI16) and anti-IFI16 antibodies have been detected in subjects with several rheumatic diseases, often correlating with disease severity, and in this study we investigated their prevalence and clinical associations in psoriatic arthritis (PsA) compared to psoriasis (Pso). We tested sera and synovial fluids of patients with PsA for IFI16 protein levels by capture enzyme-linked immunosorbent assay (ELISA) and for anti-IFI16 immunoglobulin (Ig)G and IgA by ELISA, protein radio-immunoprecipitation and immunoprecipitation-Western blot of IgG. Sera from patients with Pso and healthy subjects were used as controls, and in a subgroup of patients with PsA we also studied sera after treatment with etanercept. IFI16 was detectable in the sera of 66% of patients with Pso, 46% with PsA and 19% of controls. Among PsA cases, 51% of IFI16-positive cases had elevated levels of C-reactive protein (CRP) compared to 31% of patients with undetectable IFI16. Anti-IFI16 of both IgG and IgA isoforms were detected with significantly higher frequency in PsA and Pso compared to healthy controls, with higher IgG titres in patients with elevated C-reactive protein (CRP) (P = 0·015). Immunoprecipitation confirmed the presence of anti-IFI16 IgG antibodies and these preferentially recognized epitopes outside the N-terminus of the protein. Lastly, IFI16 was detected in one of seven and anti-IFI16 in three of seven synovial fluids from patients with PsA. Therefore, IFI16 and anti-IFI16 are detectable in serum and synovial fluid of PsA patients, especially in cases of elevated CRP.

The diagnosis and management of Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), is still challenging. There is no definitive gold standard diagnostic test, which is made on patient history and with endoscopic and histological findings. This study analyzed serum proteins and fatty acids using mass spectrometry-based techniques. Quantitation of serum proteins was performed by depleting 14 high-abundance proteins, followed by tryptic digestion and LC-MS analysis, while fatty acids were analyzed using GC-MS. Bioinformatic tools were used to identify several new potential biomarkers for an early and non-invasive diagnosis of IBD, and to differentiate CD from UC. Moreover, the diagnostic power of the MS-identified biomarkers was also corroborated by Western Blot and ELISA assays. Hence, we identified the biological functions and pathways involved in the various subsets of IBD. Coagulation, fibrinolysis and acute phase response processes were found to be strongly involved in the condition. The involvement of several fatty acids, such as anti-inflammatory mediators, was also identified. Finally, proteomic and lipidomic data were integrated by using combinatorial and multivariate analyses to discover new combined biomarkers and to study the molecular pathways involved in IBD.

Objective The interferon-inducible protein 16 (IFI16) has been detected in sera from patients with autoimmune/inflammatory diseases, but not in healthy subjects. This leaking leads to loss of tolerance toward this self-protein and the development of autoantibodies. In this study, clinical significance of both IFI16 protein and anti-IFI16 antibodies in rheumatoid arthritis (RA) was investigated. Methods IFI16 protein and anti-IFI16 antibody levels were assessed by enzyme-linked immunosorbent assay in serum samples from 154 RA patients and 182 healthy controls, and in synovial fluid (SF) samples from 21 RA patients and 25 patients with osteoarthritis (OA). Results Mean serum levels for both IFI16 and anti-IFI16 antibodies were higher in RA patients than in healthy controls, with a direct correlation between IFI16 concentration and anti-IFI16 antibody titer. The majority of RA patients with detectable circulating IFI16 protein were also positive for rheumatoid factor (RF)/anti-cyclic citrullinated peptide antibody (anti-CCP). The latter group was found to be positive for anti-IFI16 antibodies as well. The mean SF concentrations of both IFI16 protein and anti-IFI16 antibodies were higher in RA patients when compared with control OA patients. Interestingly, the presence of circulating IFI16 protein, but not anti-IFI16 antibodies, significantly correlated with RA-associated pulmonary disease. This correlation was not dependent on the presence of anti-IFI16 antibodies, sex, and smoking habit. Conclusion Our data demonstrate that the high levels of circulating IFI16 in RA are more frequent in RF/anti-CCP-positive RA patients and significantly associated with pulmonary involvement. The relevance of circulating IFI16 protein as a new clinical biomarker of RA should be verified with additional studies.

Background Inflammatory bowel disease (IBD) is characterized by a chronic inflammation of the gut, partly driven by defects in the expression and function of pattern recognition receptors, including the IFI16 protein. Because this protein is a target for autoantibodies and its aberrant expression was reported in colonic mucosa from active patients with ulcerative colitis, we studied its expression and specific seroresponse in patients with IBD before and after infliximab (IFX) therapy. Methods Anti-IFI16 antibodies (IgG and IgA subtypes) were measured in the sera of 74 patients with IBD: 48 patients with Crohn's disease (CD) and 26 patients with ulcerative colitis, prospectively harvested before and after IFX therapy. Anti-GP2 antibodies (both IgG and IgA subtypes) were also tested for comparison. The patient antibody statuses were qualitatively and quantitatively associated with disease phenotype and response to IFX therapy. Results Significantly higher titers of anti-IFI16 IgG were found in both CD and ulcerative colitis patients compared with healthy controls. Anti-IFI16 IgA titers were also present in patients with CD. Anti-GP2 IgG subtype titers were significantly increased in patients with CD, as were IgA subtype titers. Significant changes in anti-IFI16 IgG subtype titers were observed after IFX in patients with CD who correlated with clinical remission or response. Conclusions Our results highlight the importance of IFI16 in IBD pathogenesis showing that its de novo overexpression in the gut epithelial cells leads to a breakdown in immune tolerance and the subsequent development of specific autoantibodies. Anti-IFI16 IgG antibodies hold the potential to serve as a biomarker of response to IFX therapy.

IFI16 belongs to the interferon (IFN)-inducible HIN-200/Ifi-200 gene family, which encodes evolutionary related human (IFI16, IFIX, MNDA, and AIM2) and murine (Ifi202a, Ifi202b, Ifi203, Ifi204, Ifi205/D3, and Ifi206) nuclear phosphoproteins. To detect anti-IFI16 antibodies in the sera from patients affected by autoimmune disorders, a semiquantitative enzyme-linked immunosorbent assay (ELISA) was generated and characterized using a recombinant purified IFI16 protein as antigen. Anti-IFI16 titers above the 95th percentile for control subjects were observed in more than 50% of systemic lupus erythematosus (SLE) patients, 30% of systemic sclerosis (SSc) patients, and 25% of Sjogren syndrome (SjS) patients versus 6% of healthy donors. Anti-IFI16 antibodies were detected in 30% of the SSc patients who tested negative for both anticentromere (ACA) and anti-topo I (anti-Scl 70) antibodies. In this subgroup of patients, anti-IFI16 were significantly associated with the limited cutaneous form of SSc with a sensitivity of 40% and a specificity of 81%. Moreover, analysis of the distribution of anti-RNAP II antibodies versus anti-IFI16 in the same SSc population showed that they were mutually exclusive. Finally, anti-IFI16 were also significantly associated with heart involvement. In SLE patients, the prevalence and titers of anti-IFI16 antibodies were significantly higher in patients without renal involvement than in patients with glomerulonephritis (63% and 24%, respectively). Anti-IFI16 antibodies inversely correlated with proteinuria at univariate analysis and with C3 hypocomplementemia at univariate and multivariate analysis, including SLEDAI and anti-double-stranded deoxyribonucleic acid (dsDNA) as measures of disease activity. Although further studies are needed to clarify the exact mechanisms of the function of anti-IFI16 antibodies, these antibodies may serve as a new biomarker to be used in the diagnosis and assessment of disease activity in patients with SSc or SLE, with or without renal involvement.

Objective Several studies have shown the presence of anti-IFI16 antibodies in systemic lupus erythematosus (SLE), Sjögren Syndrome (SjS), systemic sclerosis (SSc) and other autoimmune diseases. However, the significance of anti-IFI16 antibodies in SLE has not been fully characterized. The aim of this study was to investigate associations between anti-IFI16 antibodies and clinical and serologic parameters of SLE. Methods An enzyme-linked immunosorbent assay (ELISA) kit was used to measure anti-IFI16 antibodies in the sera of 168 SLE patients, 46 patients with any type of primary glomerulonephritis (GN) and 182 healthy controls (HCs). Associations between anti-IFI16 antibodies and clinical and serologic parameters of SLE were statistically evaluated using both univariate and multivariate analysis. Results Significantly higher anti-IFI16 titres were observed in SLE patients compared to both non-SLE GN and HCs (median levels: 270.1 U/ml vs 132.1 U/ml, p = 0.001, and 52.9 U/ml, p Conclusions The inverse correlations observed between anti-IFI16 positivity, proteinuria and C3 hypocomplementaemia suggest that anti-IFI16 antibodies do not contribute to renal inflammation in SLE; indeed they may even prevent complement consumption. Anti-IFI16 antibodies hold the potential to serve as a new biomarker of disease activity in SLE.

Objectives The IFN-inducible protein 16 (IFI16) has been detected in sera from patients with autoimmune/inflammatory diseases but not in healthy subjects. This leaking leads to loss of tolerance towards this self-protein and development of autoantibodies. In this study, the clinical significance of both IFI16 protein and anti-IFI16 antibodies (Abs) in rheumatoid arthritis (RA) was investigated. Methods IFI16 protein and anti-IFI16 Abs levels were assessed by ELISA in serum samples from 154 RA patients and 182 healthy controls (HC), and in synovial fluid (SF) samples from 21 RA patients and 25 patients with osteoarthritis (OA). Results Mean serum levels for both IFI16 and anti-IFI16 Abs were higher in RA than in HC with a direct correlation between IFI16 concentration and anti-IFI16 Abs titer. The majority of RA patients with detectable circulating IFI16 protein were also positive for RF/ACPA. The latter group was found positive for anti-IFI16 Abs as well. The mean SF concentrations of both IFI16 protein and anti-IFI16 Abs were higher in RA when compared with control OA. Interestingly, the presence of circulating IFI16 protein, but not anti-IFI16 Abs, significantly correlated with RA-associated pulmonary disease. This correlation was not dependent on the presence of anti-IFI16 Abs, gender and smoking habit. Conclusions Our data demonstrate that the high levels of circulating IFI16 in RA are more frequent in RF/ACPA-positive RA patients and significantly associated with pulmonary involvement. The relevance of circulating IFI16 protein as new clinical biomarker of RA should be verified with additional studies.

Objectives: To validate the clinical significance of anti-IFI16 autoantibodies in SSc and assess their associations with serological markers of SSc. Methods: A semi-quantitative ELISA was used to detect anti-IFI16 autoantibodies in the sera of 344 SSc patients from seven Italian hospitals and 144 healthy controls. SSc-associated autoantibodies [anti-RNA polymerase III (anti-RNAP III) antibodies, anti-centromere, anti-topo I] and IF patterns were evaluated using commercial assays. Statistical analyses were performed to test clinical and serological associations. Results: The results of this study confirm a significant prevalence (29%) of anti-IFI16 antibodies in the SSc population (n = 344). Anti-IFI16 antibodies were also detected in 30% of the SSc patients who tested negative for both ACAs and anti-topo I (anti-Scl70) antibodies. In this subgroup of patients, anti-IFI16 antibodies were significantly associated with the limited cutaneous form of SSc with a sensitivity of 40% and a specificity of 81%. Moreover, analysis of the distribution of anti-RNAP III antibodies vs anti-IFI16 in the same SSc population showed that they were mutually exclusive. IIF revealed no association between anti-IFI16 and fluoroscopic patterns, due to a lack of IFI16 autoantigen in HEp-2 cells. Anti-IFI16 antibody levels were also significantly associated with heart involvement. Conclusions: Anti-IFI16 autoantibodies are frequently detected in SSc, displaying clinical and laboratory associations, and being particularly useful for diagnosis and disease classification in patients who are negative for other SSc serological markers. © The Author 2010. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved.