Novel cerebrospinal fluid and serum autoantibody targets for clinically isolated syndrome.

Limited information is available on the identity of antigens targeted by antibodies present in cerebrospinal fluid (CSF) of patients with clinically isolated syndrome (CIS). The aim of this study was to identify novel antigens for CIS and investigate their prognostic potential to predict conversion to multiple sclerosis (MS). We applied serological antigen selection (SAS) to identify antigens interacting with antibodies present in the pooled CSF from four CIS patients, who developed MS. Antibody reactivity towards CIS antigens identified by SAS was tested in CSF and serum from patients with CIS (n = 123/n = 108), MS (n = 65/n = 44), and other (inflammatory) neurological diseases (n = 75/n = 38) as well as in healthy control sera (n = 44). Using SAS, a panel of six novel CIS candidate antigens was identified. CSF antibody reactivity was detected in both CIS and relapsing-remitting (RR) MS. Serum reactivity was significantly increased in CIS and RR-MS as compared with controls (p = 0.03). For two antigens, the frequency of antibody-positive patients was higher in CIS patients who converted to MS as compared with CIS patients without conversion. We identified novel CIS antigens to which antibody reactivity was primarily detected in CIS and RR-MS as compared to controls. Possible prognostic potential could be demonstrated for two antigens.

Frameshifting in the p6 cDNA phage display system.

Phage display is a powerful technique that enables easy identification of targets for any type of ligand. Targets are displayed at the phage surface as a fusion protein to one of the phage coat proteins. By means of a repeated process of affinity selection on a ligand, specific enrichment of displayed targets will occur. In our studies using C-terminal display of cDNA fragments to phage coat protein p6, we noticed the occasional enrichment of targets that do not contain an open reading frame. This event has previously been described in other phage display studies using N-terminal display of targets to phage coat proteins and was due to uncommon translational events like frameshifting. The aim of this study was to examine if C-terminal display of targets to p6 is also subjected to frameshifting. To this end, an enriched target not containing an open reading frame was selected and an E-tag was coupled at the C-terminus in order to measure target display at the surface of the phage. The tagged construct was subsequently expressed in 3 different reading frames and display of both target and E-tag measured to detect the occurrence of frameshifting. As a result, we were able to demonstrate display of the target both in the 0 and in the +1 reading frame indicating that frameshifting can also take place when C-terminal fusion to minor coat protein p6 is applied.

Multiplexing approaches for autoantibody profiling in multiple sclerosis.

The preliminary positive effects of B cell depletion therapy in multiple sclerosis (MS) have renewed interest in a potential role of B cells and autoantibodies in the MS disease process. Regardless of a possible pathogenic role of the humoral immune response in MS, the analysis of autoantibodies as disease markers is valuable. Despite intense research, there is no known MS-associated antibody specificity that can individually discriminate between MS patients and controls. Due to the overlap in autoantibody profiles in autoimmune diseases, and due to the complexity of MS, multiplex autoantibody profiling approaches are needed to generate a panel of MS-associated autoantibodies with high combined sensitivity and specificity for MS. In recent years, several multiplexing approaches have been applied in MS autoantibody profiling with promising results regarding the generation of a so-called MS-specific autoantibody fingerprint. We also recently applied a high-throughput autoantibody profiling technique for MS cerebrospinal fluid resulting in the identification of a novel panel of 8 antigenic targets with 45% sensitivity and 86% specificity for the disease. Identification of MS-specific autoantibody specificities is important for the development of diagnostic and prognostic markers for MS. Moreover, it can provide more knowledge regarding underlying MS disease processes and novel therapeutic targets.

Autoantibody profiling in multiple sclerosis reveals novel antigenic candidates.

An important contribution of B cells and autoantibodies has been demonstrated in the pathogenesis of multiple sclerosis (MS), leading to interest in the use of such autoantibodies as diagnostic or prognostic biomarkers. The objective of this study was to identify novel Ab biomarkers for MS using "serological Ag selection". Using a phage display library derived from MS brain plaques, we applied serological Ag selection to identify antigenic targets specifically interacting with Abs present in the cerebrospinal fluid (CSF) of 10 relapsing-remitting MS patients. These antigenic targets were further evaluated on a large panel of CSF from 63 other MS patients, 30 patients with other inflammatory disorders, and 64 patients with noninflammatory neurological disorders. A panel of eight antigenic targets was identified that showed a 86% specificity and 45% sensitivity in discriminating MS patients and controls. Four of the antigenic targets showed exclusive reactivity (100% specificity; 23% sensitivity) in the MS group as compared with the control group. Detailed bio-informatic analyses revealed a novel Ag, SPAG16. Among the novel phage peptides identified, novel epitopes were generated from untranslated sequences and out-of-frame sequences. Of 10 relapsing-remitting patients used for serological Ag selection, Ab reactivity toward one of the eight antigenic targets was also demonstrated in serum of 38% CSF-positive patients. Autoantibody profiles against epitopes derived from MS brain tissue could serve as diagnostic markers or form the basis for the identification of a subgroup of MS patients.