Serum Peptide Immunoglobulin G Autoantibody Response in Patients with Different Central Nervous System Inflammatory Demyelinating Disorders

Previous efforts to discover new surrogate markers for the central nervous system (CNS) inflammatory demyelinating disorders have shown inconsistent results; moreover, supporting evidence is scarce. The present study investigated the IgG autoantibody responses to various viral and autoantibodies-related peptides proposed to be related to CNS inflammatory demyelinating disorders using the peptide microarray method. We customized a peptide microarray containing more than 2440 immobilized peptides representing human and viral autoantigens. Using this, we tested the sera of patients with neuromyelitis optica spectrum disorders (NMOSD seropositive, n = 6; NMOSD seronegative, n = 5), multiple sclerosis (MS, n = 5), and myelin-oligodendrocyte glycoprotein antibody-associated disease (MOGAD, n = 6), as well as healthy controls (HC, n = 5) and compared various peptide immunoglobulin G (IgG) responses between the groups. Among the statistically significant peptides based on the pairwise comparisons of IgG responses in each disease group to HC, cytomegalovirus (CMV)-related peptides were most clearly distinguishable among the study groups. In particular, the most significant differences in IgG response were observed for HC vs. MS and HC vs. seronegative NMOSD (p = 0.064). Relatively higher IgG responses to CMV-related peptides were observed in patients with MS and NMOSD based on analysis of the customized peptide microarray.

Previously unrecognized non-reproducible antibody-antigen interactions and their implications for diagnosis of viral infections including COVID-19

Antibody-antigen (Ab-Ag) interactions are canonically described by a model which exclusively accommodates non-interaction (0) or reproducible-interaction (RI) states, yet this model is inadequate to explain often-encountered non-reproducible signals. Here, by monitoring diverse experimental systems and confirmed COVID-19 clinical sera using a peptide microarray, we observed that non-specific interactions (NSI) comprise a substantial proportion of non-reproducible antibody-based results. This enabled our discovery and capacity to reliably identify non-reproducible Ab-Ag interactions (NRI), as well as our development of a powerful explanatory model ("0-RI-NRI-Hook four-state model") that is [mAb]-dependent, regardless of specificity, which ultimately shows that both NSI and NRI are not predictable yet certain-to-happen. In experiments using seven FDA-approved mAb drugs, we demonstrated the use of NSI counts in predicting epitope type. Beyond challenging the centrality of Ab-Ag interaction specificity data in serology and immunology, our discoveries also facilitated the rapid development of a serological test with uniquely informative COVID-19 diagnosis performance.

The landscape of antibody binding in SARS-CoV-2 infection

The search for potential antibody-based diagnostics, vaccines, and therapeutics for pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has focused almost exclusively on the spike (S) and nucleocapsid (N) proteins. Coronavirus membrane (M), ORF3a, and ORF8 proteins are humoral immunogens in other coronaviruses (CoVs) but remain largely uninvestigated for SARS-CoV-2. Here, we use ultradense peptide microarray mapping to show that SARS-CoV-2 infection induces robust antibody responses to epitopes throughout the SARS-CoV-2 proteome, particularly in M, in which 1 epitope achieved excellent diagnostic accuracy. We map 79 B cell epitopes throughout the SARS-CoV-2 proteome and demonstrate that antibodies that develop in response to SARS-CoV-2 infection bind homologous peptide sequences in the 6 other known human CoVs. We also confirm reactivity against 4 of our top-ranking epitopes by enzyme-linked immunosorbent assay (ELISA). Illness severity correlated with increased reactivity to 9 SARS-CoV-2 epitopes in S, M, N, and ORF3a in our population. Our results demonstrate previously unknown, highly reactive B cell epitopes throughout the full proteome of SARS-CoV-2 and other CoV proteins.

High Fidelity Cyclic Peptide Microarray to Diagnose Rheumatoid Arthritis

Introduction Antibodies reactive with cyclic citrullinated peptides (ACPA) have been included as a part of the ACR criteria for rheumatoid arthritis (RA) since 2010ii . However, due to the inability to capture the polydispersity of antibodies in RA without losing specificity, the ELISA assays cannot be used as definitive markers for diagnosis or prognosis. Current ELISA methods employ at most 30 unique cyclic citrullinated peptides for detection of ACPA. Apart from antibodies to citrullinated peptides, the serum from RA patients also contains antibodies to carbamylated antigens. Citrullinated and Carbamylated peptides hence show great promise for the improved diagnosis of RA. Here we tested whether a novel silicon-based combinatorial high-fidelity and high throughput cyclic peptide microarray that includes both citrullination and carbamylation modifications identifies RA with improved sensitivity compared to standard ELISA assays. Methods Using a cyclic modified peptide (CMP) library of more than 2 million sequences we tested 121 clinically diagnosed RA patients and compared binding profiles to corresponding linear epitopes and to commercially available CCP kits. Disease controls and samples from healthy individuals were also used to determine the specificity of the assay. The tests were performed using high throughput liquid handlers integrated with biochip imagers enabling high automation and a rapid turnaround time of 2.5 hrs. Since the citrulline and homocitrulline are very difficult to distinguish except by mass spectrometry, we will use the term Vibrant ACPA to include antibodies that react with either or both of these modified peptides in our assay. Results Using our CMP library, the sensitivity of RA detection was 95.04% with a specificity of 95.27% compared to linear peptides (Sensitivity 43.80% and Specificity 96.21%) and to commercial CCP kits (Sensitivity 66.94% and Specificity 89.20%). Inclusion of both citrullinated and carbamylated sequences provided increased sensitivity of testing (from 67% to 95%) as shown in Table 5. Some samples were only positive for carbamylated peptides and some only positive for citrullinated peptide indicating the importance of both peptide modifications.Conclusions These novel cyclic modified peptide (CMP) sequences have a high degree of accuracy in differentiating RA from controls, compared with standard serologic ELISA tests. Both citrullinated and carbamylated peptides are necessary for increasing the current sensitivity of RA testing. We also established here that a rigid conformation of the peptide is necessary for improved capture of antibodies by comparing cyclic and linear versions of the same peptide showing improved sensitivity with cyclisation. This high throughput pillar plate platform along with the 2 million data points generated per sample enable immune profiling on an unprecedented scale. While improved diagnostics is the primary outcome presented here, future identification of antigenic peptides that enable better prediction of prognosis and therapy would potentially improve outcomes in the affected population.

Scoping review of the applications of peptide microarrays on the fight against human infections.

Introduction This scoping review explores the use of peptide microarrays in the fight against infectious diseases. The research domains explored included the use of peptide microarrays in the mapping of linear B-cell and T cell epitopes, antimicrobial peptide discovery, immunosignature characterisation and disease immunodiagnostics. This review also provides a short overview of peptide microarray synthesis. Methods Electronic databases were systematically searched to identify relevant studies. The review was conducted using the Joanna Briggs Institute methodology for scoping reviews and data charting was performed using a predefined form. The results were reported by narrative synthesis in line with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews guidelines. Results Eighty-six articles from 100 studies were included in the final data charting process. The majority (93%) of the articles were published during 2010–2020 and were mostly from Europe (44%) and North America (34 %). The findings were from the investigation of viral (44%), bacterial (30%), parasitic (25%) and fungal (2%) infections. Out of the serological studies, IgG was the most reported antibody type followed by IgM. The largest portion of the studies (78%) were related to mapping B-cell linear epitopes, 10% were on diagnostics, 9% reported on immunosignature characterisation and 6% reported on viral and bacterial cell binding assays. Two studies reported on T-cell epitope profiling. Conclusion The most important application of peptide microarrays was found to be B-cell epitope mapping or antibody profiling to identify diagnostic and vaccine targets. Immunosignatures identified by random peptide microarrays were found to be applied in the diagnosis of infections and interrogation of vaccine responses. The analysis of the interactions of random peptide microarrays with bacterial and viral cells using binding assays enabled the identification of antimicrobial peptides. Peptide microarray arrays were also used for T-cell linear epitope mapping which may provide more information for the design of peptide-based vaccines and for the development of diagnostic reagents.

The landscape of antibody binding in SARS-CoV-2 infection

The search for potential antibody-based diagnostics, vaccines, and therapeutics for pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has focused almost exclusively on the spike (S) and nucleocapsid (N) proteins. Coronavirus membrane (M), ORF3a, and ORF8 proteins are humoral immunogens in other coronaviruses (CoVs) but remain largely uninvestigated for SARS-CoV-2. Here we use ultradense peptide microarray mapping to show that SARS-CoV-2 infection induces robust antibody responses to epitopes throughout the SARS-CoV-2 proteome, particularly in M, in which one epitope achieved excellent diagnostic accuracy. We map 79 B cell epitopes throughout the SARS-CoV-2 proteome and demonstrate that antibodies that develop in response to SARS-CoV-2 infection bind homologous peptide sequences in the six other known human CoVs. We also confirm reactivity against four of our top-ranking epitopes by enzyme-linked immunosorbent assay (ELISA). Illness severity correlated with increased reactivity to nine SARS-CoV-2 epitopes in S, M, N, and ORF3a in our population. Our results demonstrate previously unknown, highly reactive B cell epitopes throughout the full proteome of SARS-CoV-2 and other CoV proteins.

Systematic evaluation of SARS-CoV-2 spike protein derived peptides for diagnosis of COVID-19 patients

Serological test plays an essential role in monitoring and combating COVID-19 pandemic. Recombinant spike protein (S protein), especially S1 protein is one of the major reagents for serological tests. However, the high cost in production of S protein, and the possible cross-reactivity with other human coronaviruses poses unneglectable challenges. Taking advantage of a peptide microarray of full spike protein coverage, we analyzed 2,434 sera from 858 COVID-19 patients, sera from 63 asymptomatic patients and 610 controls collected from multiple clinical centers. Based on the results of the peptide microarray, we identified several S protein derived 12-mer peptides that have high diagnosis performance. Particularly, for monitoring IgG response, one peptide (aa 1148-1159 or S2-78) has a comparable sensitivity (95.5%, 95% CI 93.7-96.9%) and specificity (96.7%, 95% CI 94.8-98.0%) to that of S1 protein for detection of both COVID-19 patients and asymptomatic infections. Furthermore, the performance of S2-78 IgG for diagnosis was successfully validated by ELISA with an independent sample cohort. By combining S2-78/ S1 with other peptides, a two-step strategy was proposed to ensure both the sensitivity and specificity of S protein based serological assay. The peptide/s identified in this study could be applied independently or in combination with S1 protein for accurate, affordable, and accessible COVID-19 diagnosis.