Kappa free light chains is a valid tool in the diagnostics of MS: A large multicenter study.

OBJECTIVE: To validate kappa free light chain (KFLC) and lambda free light chain (LFLC) indices as a diagnostic biomarker in multiple sclerosis (MS). METHODS: We performed a multicenter study including 745 patients from 18 centers (219 controls and 526 clinically isolated syndrome (CIS)/MS patients) with a known oligoclonal IgG band (OCB) status. KFLC and LFLC were measured in paired cerebrospinal fluid (CSF) and serum samples. Gaussian mixture modeling was used to define a cut-off for KFLC and LFLC indexes. RESULTS: The cut-off for the KFLC index was 6.6 (95% confidence interval (CI) = 5.2-138.1). The cut-off for the LFLC index was 6.9 (95% CI = 4.5-22.2). For CIS/MS patients, sensitivity of the KFLC index (0.88; 95% CI = 0.85-0.90) was higher than OCB (0.82; 95%CI = 0.79-0.85; p < 0.001), but specificity (0.83; 95% CI = 0.78-0.88) was lower (OCB = 0.92; 95% CI = 0.89-0.96; p < 0.001). Both sensitivity and specificity for the LFLC index were lower than OCB. CONCLUSION: Compared with OCB, the KFLC index is more sensitive but less specific for diagnosing CIS/MS. Lacking an elevated KFLC index is more powerful for excluding MS compared with OCB but the latter is more important for ruling in a diagnosis of CIS/MS.

Peripapillary retinal nerve fibre layer thinning rate as a biomarker discriminating stable and progressing relapsing-remitting multiple sclerosis.

BACKGROUND AND PURPOSE: Peripapillary retinal nerve fibre layer (pRNFL) thickness is a strong candidate as a biomarker of axonal degeneration in multiple sclerosis (MS). The aim was to determine a cut-off value of pRNFL thinning rates in relapsing-remitting MS (RRMS) to discriminate between stable and progressing patients. METHODS: In this 3-year prospective longitudinal study on 141 RRMS patients, annual pRNFL thinning rates (aLpRNFL) were determined by individual linear regression models. The best possible cut-off value discriminating clinically progressing (physical progression or cognitive decline) and stable patients was defined by receiver operating characteristic analysis. Cut-off values were validated using a multivariate logistic regression model. RESULTS: Average aLpRNFL in progressing patients (2.4 µm, SD 2.1) was significantly higher compared to stable patients (0.5 µm, SD 1.2, P < 0.001). At a predefined specificity of 90%, aLpRNFL >1.5 µm was able to distinguish between stable and progressing RRMS with a sensitivity of 76.1%. aLpRNFL >1.5 µm was associated with a 15-fold increased risk of clinically progressing MS (P < 0.001). CONCLUSIONS: A cut-off of aLpRNFL discriminating clinically progressing and stable RRMS was identified. After validation in independent cohorts, this cut-off could be used as a biomarker of axonal degeneration supporting disease monitoring in daily clinical routine.

Cerebrospinal fluid:serum glucose ratio in the ventricular and lumbar compartments: implications for clinical practice.

BACKGROUND AND PURPOSE: Calculation of the cerebrospinal fluid:serum glucose (CSF:SGlu ) ratio is part of the routine cerebrospinal fluid (CSF) work-up. Reference values have been defined for lumbar CSF, but are lacking for ventricular CSF. The objective of this study was to investigate whether the CSF:SGlu ratio is similar in lumbar and ventricular compartments, and to determine cut-off values for CSF:SGlu ratio in ventricular CSF. METHODS: We included CSF samples that were collected by either lumbar puncture or ventricular drainage, with a red blood cell count <500/µL, normal white blood cell count and age-related normal total protein content, with simultaneously withdrawn serum sample and time to laboratory processing of ≤2 h. This resulted in 1808 sample pairs. Glucose concentrations in CSF and serum were measured by enzymatic spectrophotometry. RESULTS: The CSF:SGlu ratio was similar in ventricular and lumbar compartments after controlling for age, sex, time between sample withdrawal and laboratory processing, CSF white blood cell and red blood cell count, CSF total protein and serum glucose concentration using a multiple linear regression model. Lower limits for CSF:SGlu ratio in the ventricular compartment, defined as 5th percentile, were 0.51 for patients with serum glucose concentration < 100 mg/dL, 0.45 for those with serum glucose concentration ≥ 100 mg/dL and <150 mg/dL, and 0.36 for those with serum glucose concentration ≥150 mg/dL. CONCLUSIONS: The CSF:SGlu ratio was similar in the ventricular and lumbar compartments, and depended mainly on time to laboratory processing and absolute serum glucose levels. Previously established lower limits for CSF:SGlu ratio in lumbar CSF can be also applied for ventricular CSF.

Quantitation of intrathecal immunoglobulin synthesis - a new empirical formula.

BACKGROUND AND PURPOSE: Intrathecal immunoglobulin (Ig) synthesis occurs in various chronic inflammatory neurological diseases. Different formulae have been developed for quantitative determination of Ig synthesis within the cerebrospinal fluid (CSF) compartment. The hyperbolic formula of Reiber is frequently used which, however, returns a considerable number of false positive results in empirical observations. METHODS: A computerized database of more than 19 000 paired CSF and serum samples was screened for patients presumed negative for local Ig synthesis and a new formula characterizing this collective was calculated. The validity of this formula was confirmed by several validation steps. RESULTS: A cohort of 1173 patients with normal CSF findings was used for quantile regression. The 97.5th quantile of the formula Qlim(IgX)=a×Qalbb was considered as the cut-off curve for intrathecal Ig synthesis using different constants a and b for IgG, IgA and IgM. Compared to the Reiber formula, a lower level of false positive results was produced especially for IgM and IgA which was confirmed in a separate clinically well defined validation cohort. In 77 patients with discrepant findings between Reiber and our formula no specific diagnoses were found confirming the low diagnostic value of borderline Ig synthesis. CONCLUSIONS: A new approximation formula was developed for determination of intrathecal Ig synthesis which produces fewer false positive results without reducing diagnostic sensitivity.

Standardizing terms, definitions and concepts for describing and interpreting unwanted immunogenicity of biopharmaceuticals: recommendations of the Innovative Medicines Initiative ABIRISK consortium.

Biopharmaceuticals (BPs) represent a rapidly growing class of approved and investigational drug therapies that is contributing significantly to advancing treatment in multiple disease areas, including inflammatory and autoimmune diseases, genetic deficiencies and cancer. Unfortunately, unwanted immunogenic responses to BPs, in particular those affecting clinical safety or efficacy, remain among the most common negative effects associated with this important class of drugs. To manage and reduce risk of unwanted immunogenicity, diverse communities of clinicians, pharmaceutical industry and academic scientists are involved in: interpretation and management of clinical and biological outcomes of BP immunogenicity, improvement of methods for describing, predicting and mitigating immunogenicity risk and elucidation of underlying causes. Collaboration and alignment of efforts across these communities is made difficult due to lack of agreement on concepts, practices and standardized terms and definitions related to immunogenicity. The Innovative Medicines Initiative (IMI; www.imi-europe.org), ABIRISK consortium [Anti-Biopharmaceutical (BP) Immunization Prediction and Clinical Relevance to Reduce the Risk; www.abirisk.eu] was formed by leading clinicians, academic scientists and EFPIA (European Federation of Pharmaceutical Industries and Associations) members to elucidate underlying causes, improve methods for immunogenicity prediction and mitigation and establish common definitions around terms and concepts related to immunogenicity. These efforts are expected to facilitate broader collaborations and lead to new guidelines for managing immunogenicity. To support alignment, an overview of concepts behind the set of key terms and definitions adopted to date by ABIRISK is provided herein along with a link to access and download the ABIRISK terms and definitions and provide comments (http://www.abirisk.eu/index_t_and_d.asp).

Supratentorial white matter blurring associated with voltage-gated potassium channel-complex limbic encephalitis.

INTRODUCTION: Limbic encephalitis (LE) associated with voltage-gated potassium channel-complex antibodies (VGKC-LE) is frequently non-paraneoplastic and associated with marked improvement following corticosteroid therapy. Mesial temporal lobe abnormalities are present in around 80 % of patients. If associated or preceded by faciobrachial dystonic seizures, basal ganglia signal changes may occur. In some patients, blurring of the supratentorial white matter on T2-weighted images (SWMB) may be seen. The purpose of this study was to evaluate the incidence of SWMB and whether it is specific for VGKC-LE. METHODS: Two experienced neuroradiologists independently evaluated signal abnormalities on FLAIR MRI in 79 patients with LE while unaware on the antibody type. RESULTS: SWMB was independently assessed as present in 10 of 36 (28 %) compared to 2 (5 %) of 43 non-VGKC patients (p = 0.009). It was not related to the presence of LGI1 or CASPR2 proteins of VGKC antibodies. MRI showed increased temporomesial FLAIR signal in 22 (61 %) VGKC compared to 14 (33 %) non-VGKC patients (p = 0.013), and extratemporomesial structures were affected in one VGKC (3 %) compared to 11 (26 %) non-VGKC patients (p = 0.005). CONCLUSION: SWMB is a newly described MRI sign rather specific for VGKC-LE.

Early detection of neutralizing antibodies to interferon-beta in multiple sclerosis patients: binding antibodies predict neutralizing antibody development.

BACKGROUND: Neutralizing antibodies (NAb) affect efficacy of interferon-beta (IFN-b) treatment in multiple sclerosis (MS) patients. NAbs evolve in up to 44% of treated patients, usually between 6-18 months on therapy. OBJECTIVES: To investigate whether early binding antibody (BAb) titers or different IFN-b biomarkers predict NAb evolution. METHODS: We included patients with MS or clinically isolated syndrome (CIS) receiving de novo IFN-b treatment in this prospective European multicenter study. Blood samples were collected at baseline, before and after the first IFN-b administration, and again after 3, 12 and 24 months on that therapy; for determination of NAbs, BAbs, gene expression of MxA and protein concentrations of MMP-9, TIMP-1, sTRAIL, CXCL-10 and CCL-2. RESULTS: We found that 22 of 164 (13.4%) patients developed NAbs during a median time of 23.8 months on IFN-b treatment. Of these patients, 78.9% were BAb-positive after 3 months. BAb titers ≥ 1:2400 predicted NAb evolution with a sensitivity of 74.7% and a specificity of 98.5%. Cross-sectionally, MxA levels were significantly diminished in the BAb/NAb-positive samples; similarly, CXCL-10 and sTRAIL concentrations in BAb/NAb-positive and BAb-positive/NAb-negative samples, respectively, were also diminished compared to BAb/NAb-negative samples. CONCLUSIONS: BAb titers reliably predict NAbs. CXCL-10 is a promising sensitive biomarker for IFN-b response and its abrogation by anti-IFN-b antibodies.

Olfactory threshold is impaired in early, active multiple sclerosis.

BACKGROUND: Olfactory dysfunction has been reported in multiple sclerosis (MS). However, to date no data are available on different qualities of olfactory function, namely odour identification, odour discrimination and odour perception threshold. OBJECTIVE: To assess different qualities of olfactory function in patients with MS and correlate these with demographic data, clinical data, depression, quality of life and cognitive functions. METHODS: In this cross-sectional study, 50 patients with MS or clinically isolated syndrome and 30 healthy controls were included. Olfactory function was measured using the Sniffin' Sticks test. RESULTS: The scores for odour identification (p = 0.001), odour perception threshold (p = 0.037) and the combined score of odour identification, discrimination and perception threshold (TDI, p = 0.002) were significantly lower in MS. Hyposmia for identification (p = 0.0017), threshold (p = 0.017) and TDI score (p = 0.0014) was more frequent in MS. Olfactory threshold was impaired in patients who were clinically active in the previous year (p = 0.026) and in patients with a disease duration less than 2 years (p = 0.0093). Identification score was negatively correlated with disease duration (p = 0.0017). Olfactory function was not associated with disability, depression or quality of life. CONCLUSIONS: We report evidence for qualitatively distinct hyposmia in MS, with increased smell threshold in the early inflammatory phases of the disease and impaired identification with a more widespread chronic disease.

Decision-making for and impact of early immunomodulatory treatment: the Austrian Clinically Isolated Syndrome Study (ACISS).

BACKGROUND AND PURPOSE: When to start disease-modifying treatment (DMT) in patients with a clinically isolated syndrome (CIS) requires individual weighing of benefits versus possible burden of side effects and costs. How this occurs in a routine setting is barely known. The aim of the study was to investigate the decision-making process regarding immediate or later DMT and the ensuing impact on CIS patients in Austria. METHODS: Demographic and (para) clinical characteristics of 296 CIS patients were recorded in 29 multiple sclerosis (MS) centres, and the patients' overall condition was rated on a visual analogue scale (VAS). Clinical follow-up and VAS ratings were repeated at 6-month intervals over 2 years. The decision for initiation of DMT was at the physician's and patient's discretion. RESULTS: In 29% of patients, DMT was started within 3 months and this decision was independently associated with a T2-lesion number >or=9 on MRI and a worse VAS rating by the physician. DMT initiation in the subsequent 6 months was additionally associated with the presence of oligoclonal bands and rarely occurred thereafter. Adapted to the clinical course, later treatment was associated with the highest rate of conversion to clinically definite MS and greatest disability after 2 years whilst never treated patients fared best. Patient VAS ratings significantly improved during follow-up independently of treatment decisions. CONCLUSION: The management of Austrian CIS patients relies strongly on MRI findings and the physicians' interpretation of the patients' overall situation which, after 2 years, depends primarily on the course of the disease.

A type I interferon signature in monocytes is associated with poor response to interferon-beta in multiple sclerosis.

The effect of interferon-beta in multiple sclerosis is modest and many patients do not respond to treatment. To date, no single biomarker reliably correlates with responsiveness to interferon-beta in multiple sclerosis. In the present study, genome-wide expression profiling was performed in peripheral blood mononuclear cells from 47 multiple sclerosis patients treated with interferon-beta for a minimum of 2 years and classified as responders and non-responders based on clinical criteria. A validation cohort of 30 multiple sclerosis patients was included in the study to replicate gene-expression findings. Before treatment, interferon-beta responders and non-responders were characterized by differential expression of type I interferon-induced genes with overexpression of the type interferon-induced genes in non-responders. Upon treatment the expression of these genes remained unaltered in non-responders, but was strongly upregulated in responders. Functional experiments showed a selective increase in phosphorylated STAT1 levels and interferon receptor 1 expression in monocytes of non-responders at baseline. When dissecting this type I interferon signature further, interferon-beta non-responders were characterized by increased monocyte type I interferon secretion upon innate immune stimuli via toll-like receptor 4, by increased endogenous production of type I interferon, and by an elevated activation status of myeloid dendritic cells. These findings indicate that perturbations of the type I interferon signalling pathway in monocytes are related to lack of response to interferon-beta, and type I interferon-regulated genes may be used as response markers in interferon-beta treatment.

EFNS guidelines on disease-specific CSF investigations.

We reviewed the literature for disease-specific markers in cerebrospinal fluid (CSF) and evaluated their diagnostic and prognostic relevance in neurological diseases. High tau protein in combination with low amyloid beta levels has a high sensitivity (80%) and specificity (90%) for Alzheimer's disease (AD) against normal aging and can predict conversion of mild cognitive impairment to AD. The detection of 14-3-3 has a high sensitivity (80-90%) and specificity (90%) for the diagnosis of CJD. Low or undetectable CSF hypocretin-1 (orexin-1) levels constitute a diagnostic biomarker for narcolepsy with cataplexy. Detection of beta-2-transferrin indicates CSF contamination in oto- and rhinorrhoe with a sensitivity of > 79% at a specificity of 95% similar to the beta-trace protein (sensitivity > 90%, specificity 100%). However, beta-trace protein is faster and cheaper to perform. Possible future biomarkers are: elevated levels of vascular endothelial growth factor are relatively sensitive (51-100%) and specific (73-100%) for leptomeningeal metastases from solid tumors and are associated with a poor prognosis in this condition. Elevated CSF neurofilament (Nf) levels probably reflect acute neuronal degeneration. The prognostic value of CSF Nf levels is highest in acute conditions such as subarachnoid hemorrhage, acute optic neuritis and neuromyelitis optica.

MxA protein--an interferon beta biomarker in primary progressive multiple sclerosis patients.

BACKGROUND AND PURPOSE: Interferon beta (IFNbeta) preparations have some effect on the progressive phase of multiple sclerosis (MS). This limited effect might be partially because of a certain number of IFNbeta non-responders. Myxovirus resistance protein A (MxA)--a marker of IFNbeta bioactivity--was correlated with the clinical response during an uncontrolled trial, investigating the safety of IFNbeta-1b in primary progressive (PPMS) patients. METHODS: Twenty PPMS were treated with IFNbeta-1b (s.c.) for 1 year. Blood samples were taken before and 1, 2, 3, 6, 9, 12, and 15 months after treatment initiation and MxA protein levels were measured. Patients were clinically evaluated by EDSS and the more sensitive Incapacity Status Scale (ISS) and stratified in a stable and a progressing group. RESULTS: Using ISS criteria, 11 patients remained stable and nine patients progressed during treatment. The mean area under the curve of log MxA levels during treatment were significantly higher in stable than in progressing patients (10.87 vs. 5.99; P = 0.002). CONCLUSION: A good biological response to IFNbeta might be associated with a better clinical effect of this drug and could be helpful in future clinical studies for early identification of treatment responders.

Combined evaluation of personality, risk and coping in MS patients: A step towards individualized treatment choice - The PeRiCoMS-Study I.

BACKGROUND: Multiple sclerosis (MS) is a chronic inflammatory neurological disease requiring disease-modifying treatment (DMT). To provide patients with the optimal individual therapeutic option, treatment recommendations should be based not only on individual disease course and DMT specific benefit-risk estimates, but also on patient's individual characteristics such as personality, risk attitude and coping strategies. However, these characteristics are difficult to objectify in clinical routine practice without the support of appropriate evaluation instruments. OBJECTIVE: To identify and to assemble an objective test battery measuring personality, risk attitude and coping strategies in MS patients. METHODS: A comprehensive literature search was performed to obtain all questionnaires assessing personality, risk attitude and coping strategies. Availability in German language, validation in a published normative collective and a reliability of >0.70 were required for our purposes. Based on these criteria, we chose the Big-Five-Personality Test, UPPS Impulsive Behaviour Scale, Domain-Specific Risk-Taking scale (DOSPERT), Brief-COPE and Stress & Coping Inventory (SCI). Results were compared to published normative controls of the respective questionnaires. RESULTS: Out of 22 MS patients (7 males, 15 females) participating in this study, 19 (86.4%) completed all questionnaires. The median completion time was 45min (min-max range: 25-60min). The median scores of the MS group were within the average range of published control samples in all questionnaires. CONCLUSIONS: We report that traits of personality, risk attitude and coping strategies can be effectively and feasibly tested in MS patients by the instruments used in our exploratory study. There were no differences between MS patients and healthy controls, thus enabling assessment without being influenced by the diagnosis of MS. After validation in a larger cohort the "PeRiCoMS"-battery will be useful as another step towards a more individualized shared-decision-making in every day routine practice.

Interferon-beta antibodies have a higher affinity in patients with neutralizing antibodies compared to patients with non-neutralizing antibodies.

In this study, we investigated the affinity, determined by a relative affinity assay, using increasing concentrations of sodium-isothiocyanate to disrupt the antigen antibody binding of neutralizing and non-neutralizing antibodies against interferon-beta (IFNbeta)-1a and -1b in 73 serum samples of MS patients treated with IFNbeta-1a or -1b. Relative affinity values were significantly higher in NAB-positive compared to NAB-negative samples and in samples of IFNbeta-1a-treated patients compared to IFNbeta-1b. A significant positive correlation between relative affinity values and therapy duration indicates affinity maturation as another qualitative factor in IFNbeta neutralization.

Guidelines on routine cerebrospinal fluid analysis. Report from an EFNS task force.

A great variety of neurological diseases require investigation of cerebrospinal fluid (CSF) to prove the diagnosis or to rule out relevant differential diagnoses. The objectives were to evaluate the theoretical background and provide guidelines for clinical use in routine CSF analysis including total protein, albumin, immunoglobulins, glucose, lactate, cell count, cytological staining, and investigation of infectious CSF. The methods included a Systematic Medline search for the above-mentioned variables and review of appropriate publications by one or more of the task force members. Grading of evidence and recommendations was based on consensus by all task force members. It is recommended that CSF should be analysed immediately after collection. If storage is needed 12 ml of CSF should be partitioned into three to four sterile tubes. Albumin CSF/serum ratio (Qalb) should be preferred to total protein measurement and normal upper limits should be related to patients' age. Elevated Qalb is a non-specific finding but occurs mainly in bacterial, cryptococcal, and tuberculous meningitis, leptomingeal metastases as well as acute and chronic demyelinating polyneuropathies. Pathological decrease of the CSF/serum glucose ratio or increased lactate concentration indicates bacterial or fungal meningitis or leptomeningeal metastases. Intrathecal immunoglobulin G synthesis is best demonstrated by isoelectric focusing followed by specific staining. Cellular morphology (cytological staining) should be evaluated whenever pleocytosis is found or leptomeningeal metastases or pathological bleeding is suspected. Computed tomography-negative intrathecal bleeding should be investigated by bilirubin detection.

Immunoglobulin subclasses in patients with neutralizing and nonneutralizing antibodies against IFN-beta1b.

Treatment of multiple sclerosis (MS) with interferon-beta1b (IFN-beta1b) induces the production of antibodies in some patients. A proportion of these antibodies can reduce the biologic activity of IFN-beta, and they are, therefore, referred to as neutralizing antibodies (NAB). The remaining antibodies do not interfere with the biologic activity of IFN-beta and are referred to as nonneutralizing antibodies (NNAB) in this paper. Immunoglobulin (Ig) subtyping of these antibodies was carried out, and Ig subclass patterns in 20 patients with NAB were compared with those of NNAB in 39 patients. In patients with NAB, IgG2 and IgG4 were found to occur more frequently than in patients with NNAB (30% vs. 3%, p = 0.05, and 55% vs. 18%, p = 0.003, respectively) The NAB titer correlated strongly with the IgG4 titer (r = 0.53, p = 0.02). Median total IgG, IgG1, and IgG4 titers were significantly higher in NAB than in NNAB patients (respectively, 8000 vs. 3200, p = 0.01; 1600 vs. 400, p = 0.0004; 200 vs. 0, p = 0.004). It is concluded that the development of NAB is related to both the quantity and the quality of the antibodies against IFN-beta1b.

A comparative study of the relative bioavailability of different interferon beta preparations.

BACKGROUND: Three different recombinant interferon beta (IFNbeta) preparations are currently available for the treatment of MS, two IFNbeta-1a products (Rebif and Avonex) and one IFNbeta-1b product (Betaferon). These products differ with respect to the recommended dose, the dosage regimen, and the injection route. This study compared the relative biologic activity of these three products in vitro and in vivo. METHODS: Blood samples were collected from 237 patients with MS (170 on IFNbeta therapy and 67 control subjects receiving no therapy). Samples with neutralizing antibodies were excluded. Levels of the antiviral protein MxA and soluble vascular cell adhesion molecule-1 (sVCAM) in the four groups were measured by ELISA. In the in vitro investigation, untreated blood was incubated for 24 hours with increasing concentrations of the three IFNs from a dose of 1 IU/mL to 1000 IU/mL, after which levels of MxA were measured. RESULTS: A difference between the groups was observed in vitro, with a significant change from baseline in MxA levels being observed at 10 IU for Betaferon compared with 100 IU for Rebif and Avonex. However, this might be due to the different methods used for the determination of IU by the manufacturers. At the single-dose level there were no significant differences between IFNbeta preparations. In vivo, there were significantly different levels of MxA in the four groups. In the Betaferon group, the median value for MxA was 2.29 ng/105 peripheral blood leukocytes (PBL), compared with 1.00 ng/105 PBL for Rebif, 0.57 ng/105 PBL for Avonex, and 0.14 ng/105 PBL for the control group. Some significant differences between the groups were also apparent with respect to levels of sVCAM, which were higher with Betaferon than with Rebif. CONCLUSION: IFNbeta-1b induces higher levels of the above markers of IFNbeta bioactivity than either of the two IFNbeta-1a preparations. Moreover, there is a less striking difference between the two IFNbeta-1a preparations in favor of subcutaneous IFNbeta-1a.

Bioavailability of interferon beta 1b in MS patients with and without neutralizing antibodies.

BACKGROUND: Neutralizing antibodies (NAB) to interferon beta (IFNbeta) occur in about one-third of MS patients treated with IFNbeta-1b and there is an association with a loss of clinical and MRI efficacy. However, there are no data regarding the bioavailability of IFNbeta-1b in patients with and without NAB. METHODS: The authors measured MxA in whole blood by ELISA, and serum-binding antibodies (SBA) by Western blot and ELISA in 134 samples of MS patients on IFNbeta-1b and 54 control subjects, and correlated the MxA levels and SBA titers with the NAB titer. RESULTS: In the IFNbeta group 84 samples were NAB negative, 21 were NAB positive (i.e., titer of > or =20), and 29 had detectable NAB (i.e., titer between 10 and 20). The median MxA concentration in NAB-negative patients was 4.09 ng/10(5) peripheral blood leukocytes (PBL), 2.37 ng/10(5) PBL in samples with detectable NAB, 0.36 ng/10(5) PBL in NAB-positive samples, and 0.27 ng/10(5) PBL in control subjects. There was no significant difference between NAB-positive samples and control subjects, otherwise the groups differed significantly from each other. SBA occurred in 49% of NAB-negative samples, in 79% of samples with detectable NAB, and in all NAB-positive samples. With regard to the SBA titer, all groups differed significantly from each other. In none of the control samples were SBA detected. CONCLUSION: The conversion of SBA into NAB depends to some degree on the SBA titer, but other mechanisms may be involved. Once NAB have developed, the bioavailability of IFNbeta as measured by MxA is completely inhibited.