Intrathecal immunoglobulin synthesis. Comparison of various formulae with the 'gold standard' of isoelectric focusing

Cerebrospinal Fluid Findings in 541 Patients With Clinically Isolated Syndrome and Multiple Sclerosis: A Monocentric Study

Background

Reports on typical routine cerebrospinal fluid (CSF) findings are outdated owing to novel reference limits (RL) and revised diagnostic criteria of Multiple Sclerosis (MS).

Objective

To assess routine CSF parameters in MS patients and the frequency of pathologic findings by applying novel RL.

Methods

CSF white blood cells (WBC), CSF total protein (CSF-TP), CSF/serum albumin quotient (Q_alb), intrathecal synthesis of immunoglobulins (Ig) A, M and G, oligoclonal IgG bands (OCB) were determined in patients with clinically isolated syndrome (CIS) and MS.

Results

Of 541 patients 54% showed CSF pleocytosis with a WBC count up to 40/μl. CSF cytology revealed lymphocytes, monocytes and neutrophils in 99%, 41% and 9% of patients. CSF-TP and Q_alb were increased in 19% and 7% applying age-corrected RL as opposed to 34% and 26% with conventional RL. Quantitative intrathecal IgG, IgA and IgM synthesis were present in 65%, 14% and 21%; OCB in 95% of patients. WBC were higher in relapsing than progressive MS and predicted, together with monocytes, the conversion from CIS to clinically definite MS. Intrathecal IgG fraction was highest in secondary progressive MS.

Conclusions

CSF profile in MS varies across disease courses. Blood-CSF-barrier dysfunction and intrathecal IgA/IgM synthesis are less frequent when the novel RL are applied.

Free light chains in the cerebrospinal fluid. Comparison of different methods to determine intrathecal synthesis

Background Free light chains (FLC) have been proposed as diagnostic biomarkers in the cerebrospinal fluid (CSF) of patients with inflammatory central nervous system (CNS) diseases. However, which method to use for determining an intrathecal FLC synthesis has not yet been clarified. The objective of this study was to compare the diagnostic performance of CSF FLC concentration, FLC quotient (QFLC), FLC index and FLC intrathecal fraction (FLCIF). Methods κ- and λ-FLC were measured by nephelometry under blinded conditions in CSF and serum sample pairs of patients with clinically isolated syndrome (CIS; n = 60), multiple sclerosis (MS; n = 60) and other neurological diseases (n = 60) from four different MS centers. QFLC was calculated as the ratio of CSF/serum FLC concentration, the FLC index as QFLC/albumin quotient and the percentage FLCIF by comparing QFLC to a previously empirically determined, albumin quotient-dependent reference limit. Results CSF FLC concentration, QFLC, FLC index and FLCIF of both the κ- and λ-isotype were significantly higher in patients with CIS and MS than in the control group, as well as in oligoclonal bands (OCB) positive than in OCB negative patients. Each parameter was able to identify MS/CIS patients and OCB positivity, however, diagnostic performance determined by receiver operating characteristic (ROC) analyses differed and revealed superiority of FLC index and FLCIF. Conclusions These findings support the diagnostic value of FLC measures that correct for serum FLC levels and albumin quotient, i.e. blood-CSF barrier function.

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.

Comparaison de l’immunofixation après électrophorèse sur gel d’agarose avec la focalisation isoélectrique dans la détection des bandes oligoclonales d’IgG du liquide céphalo-rachidien de patients atteints de sclérose en plaques

INTRODUCTION

Intrathecal immunoglobulins (Ig) synthesis, reflected by oligoclonal bands (OCBs) in cerebrospinal fluid (CSF) is observed in up to 90 percent of patients with clinically definite Multiple Sclerosis (MS). The gold standard laboratory test to establish the presence of OCBs in CSF of MS patients is isoelectric focusing (IEF). However, a quicker and less expensive method has been developed: immunofixation (IF).

METHODS

The aim of this study was to compare these two methods carried out 74 CSF/serum pairs of MS, 103 CSF/serum pairs of subject controls and to determine their sensitivity and specificity.

RESULTS

The agreement between results from IEF and IF was excellent (Kappa = 0.84). IEF sensitivity (78 percent) was not significantly different from that of IF (74 percent) (p = 0.3). Similarly, the specificity of IEF (93 percent) was not significantly different from that of IF (95 percent) (p = 0.2).

CONCLUSION

IF is a semi automated method which is easier to perform than IEF and which appears to be as efficient as IEF.

Le profil cytoimmunologique du LCR lors du diagnostic précoce de la sclérose en plaques

The purpose of this paper is to report cerebrospinal fluid (CSF) findings in multiple sclerosis (MS) from our laboratory, to discuss the implications of CSF abnormalities in terms of diagnosis. Paired CSF-serum samples from of 1533 on 3893 patients with suspected neurological diseases over a 10 year period were analysed by routine laboratory microscopy and assays of immunoglobulin G by isoelectric focusing for the detection of intrathecal oligoclonal IgG. Patients were grouped further into four headings according to their disorders: MS (625 cases), definite (246 cases) probable (123 cases) and possible (256 cases) according to Poser, others inflammatory neurological diseases (91 cases), various non-inflammatory neurological disorders (732 cases) and uncertain neurological disorders (85 cases). Definite MS group (16%) was compared to non-inflammatory neurological disorders (48%). Important signs for activity of multiple sclerosis are observed. Cell counts were 10/microl in 71% (N < or =2/microl). Inflammatory cytology is observed after concentration and cytocentrifugation on slides with activated B-lymphocytes, lymphoplasmocytes and/or plasmocytes (76%), total protein concentration is increased in 37% (N < 0.40g/l), CSF/serum albumin quotient with age dependent references for the blood-CSF barrier dysfunction is increased in 26% (N < 0.65 x 10(-2)), IgG index for intrathecal synthesis of IgG is increased in 69% (N < 0.70), sensitive detection of oligoclonal IgG restricted to CSF by isoelectric focusing is positive in 91% (86-96%) with a specificity of 96% (93-99%).

Distinct heterogeneity of IgG immune response in cerebrospinal fluid (CSF) detected by isoelectric focusing (IEF) with extended immunofixation

An optimized automated IEF procedure in polyacrylamide micro gels and immunofixation with 10 monospecific antibodies against some fragments of the IgG molecule and against the whole IgG isotypes IgG(1), IgG(2), IgG(3), IgG(4), respectively, detected oligoclonal bands (OBs) within acid, neutral, and alkaline ranges of the gels. Accuracy and reliability of the OB assay for detection of an intrathecal IgG synthesis proved to be higher with immunofixation than with silver staining of bands precipitated by trichloroacetic acid. CSF OBs were specified as lambda or kappa IgG subfractions, respectively, duplex IgGs precipitated with anti-lambda, anti-kappa, and anti-Fc antibodies at the same pI. Most of OBs were classified as belonging to either IgG(1), IgG(2), IgG(3), or IgG(4) isotypes in CSF. The IEF procedure additionally allowed the discrimination of both free light chains and possible "free" heavy gamma chain fragments in CSF, when immunofixation was done with monospecific antibodies against both light chains and gamma chain fragments (e.g. anti-F(ab')(2), anti-Fd, anti-Fc, anti-C(H)2). The results pointed out a distinct heterogeneity of the IgG immune response in human CSF. The IEF procedure with extended immunofixation is recommended for completion of the basic laboratory procedures used in neuroimmunology in order to discriminate inflammatory processes in human CNS.

Molecular heterogeneity, detected by two electrophoretic micro procedures, of IgG in human cerebrospinal fluid (CSF)

Semi-automated electrophoretic procedures in the PhastSystem (Amersham Pharmacia Biotech) with micro polyacrylamide gels (PAGs) and SDS-PAG gradients were modified to analyze IgG in human cerebrospinal fluid (CSF) and matched serum samples with respect to the molecular IgG structure L-H-H-L. Isoelectric focusing (IEF) with specific immunofixation detected discrete IgG bands in CSF standing out against a polyclonal and monoclonal background pattern in CSF and serum; they were denoted oligoclonal bands (IgG OBs) (OB assay positive) indicating IgG synthesis in the central nervous system (CNS) of patients with subacute and chronic processes of inflammatory CNS disorders; assay was negative with identical (mirror) bands in CSF and serum for other CNS processes. IgG OBs were specified as lambda (kappa) IgG subfractions, precipitated with the anti-light (L) chains lambda (kappa) and anti-heavy (H) chain fragments (Fd, Fc, C(H)2) as well as with anti-F(ab')(2), and as duplex IgGs with kappa and lambda OBs at the same pI. With SDS-PAG gradient electrophoresis and specific immunofixation more than six IgG fractions were detected and classed according to apparent molecular weights of a S-sulfonated human IgG standard; they were characterized with the monospecific antibodies against the L and H chain fragments as 25, 50, 75, 100, 125 and 150 kD fractions containing combinations of L and H chains as well as mixtures of both L and H chain fragments of varying dimensions. Generally, this molecular IgG heterogeneity could not be connected with the IgG OB heterogeneity revealed by IEF; but single OBs in the strongly alkaline pH region of PAG may correspond to H fragments with basic pI. Nevertheless, evidence for the existence of both free L chains and the free H chain were revealed as specific OBs with IEF and with the anti-L and anti-H antibodies in the 25 kD and 50 kD fractions, respectively, of CSF samples of six patients with diverse CNS diseases. Further experiments are needed to elicit the origin of the molecular IgG heterogeneity during the immune response of subacute and chronic inflammatory processes in human CNS.

Reporting cerebrospinal fluid data: knowledge base and interpretation software

The compilation of cerebrospinal fluid (CSF) patient data together with a graphic display of immunoglobulin patterns in a single CSF report has two main advantages: analytical and clinical plausibility control of a complex set of data improves quality assessment and allows improved clinical specificity and sensitivity for recognition of disease-related "typical" data patterns. The widespread use of automated on-line evaluation programs can now be combined with knowledge-based programs for interpretation by clinical chemists and neurologists. These programs are based on knowledge of neuroimmunology, blood-CSF barrier function and dysfunction, influence of CSF flow on concentrations of blood-derived and brain-derived proteins in CSF, specific intrathecal antibody synthesis and relevance of brain proteins for differential diagnosis of degenerative diseases. The relevance of hyperbolic discrimination functions in quotient diagrams for the detection of intrathecal immunoglobulin synthesis is compared with earlier, still frequently used, linear interpretation functions. Differences found in commercially available interpretation software are discussed.

Cerebrospinal fluid analysis: disease-related data patterns and evaluation programs

Cerebrospinal fluid (CSF) analysis is a basic tool for diagnosis of neurological diseases. Knowledge regarding blood-CSF barrier function (molecular flux/CSF flow theory) and neuroimmunology is reviewed to aid understanding and evaluation of CSF data. Disease-related immunoglobulin patterns (IgG, IgA, IgM with reference to albumin) are described in CSF/serum quotient diagrams with the hyperbolic reference range for blood-derived protein fractions in CSF. Clinical relevance of complementary analyses (cytology, PCR, oligoclonal IgG, antibody detection and brain-derived proteins) is briefly discussed. Integrated CSF data reports are shown with numerical and graphical data representation, reference range-related interpretation and diagnosis-related comments. The principles and rationale of general CSF analysis reported in this review should enable the reader to accurately interpret CSF data profiles, and to plan a proper evaluation of new brain- or blood-derived analytes in CSF.

Epstein-Barr virus nuclear antigen-1 (EBNA-1) associated oligoclonal bands in patients with multiple sclerosis

Oligoclonal bands (OCBs) are frequently observed in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS), but the target antigens of these antibodies remain unknown. We used antigen specific immunoblotting to determine whether Epstein Barr virus nuclear antigen-1 (EBNA-1) was a target of the OCBs in the CSF of patients with MS. Antibody indices (AIs) were measured by ELISA and calculated by the formula of Reiber and Lange which includes correction factors for both breakdown of the blood brain barrier and intrathecal polyclonal IgG synthesis. A distinctive oligoclonal antigen specific banding pattern for EBNA-1 was observed in 5/15 MS patients, but 0/12 controls (P=0.037, Fisher's Exact Probability). AIs in this EBNA-l positive subgroup were extremely high, comparable with levels observed in viral CNS infections. In one patient with EBNA-1 specific OCBs, EBNA-1 and a peptide 'equivalent', p62, were able to absorb a component of the total IgG. Our results suggest that in a subset of MS patients, EBNA-1 may be a major target of selected OCBs.

Evaluation of formulae for CSF IgG synthesis using data obtained from two methods: importance of receiver operator characteristic curve analysis

AIMS

To determine the clinical performance of three cerebrospinal fluid (CSF) IgG synthesis formulae using data obtained from two quantitation methods.

METHODS

Receiver operator characteristic (ROC) analysis and decision index plots were used to compare a rate nephelometric (RN) and a rocket immunoelectrophoretic (RIEP) method for quantitating albumin and IgG for use in CSF IgG synthesis formulae. Further analysis was used to determine the most clinically accurate of these formulae for a diagnosis of multiple sclerosis with regard to technical accuracy and cost effectiveness.

RESULTS

Values for albumin and IgG determined by RN gave better sensitivities and specificities than the RIEP method when applied to all three formulae; however, when the 95% confidence limits were considered, the difference was not significant. Using the RN method with an agreed "rule in" threshold value of 90% specificity, the IgG index gave the best clinical performance.

CONCLUSION

ROC curve analysis and decision index plots provide valuable tools in assessing and comparing the clinical performance of new and existing laboratory assays.

Cerebrospinal fluid in the diagnosis of multiple sclerosis: a consensus report

The Committee of the European Concerted Action for Multiple Sclerosis (Charcot Foundation) organised five workshops to discuss CSF analytical standards in the diagnosis of multiple sclerosis. This consensus report from 12 European countries summarises the results of those workshops. It is hoped that neurologists will confer with their colleagues in clinical chemistry to arrange the best possible local practice. The most sensitive method for the detection of oligoclonal immunoglobulin bands is isoelectric focusing. The same amounts of IgG in parallel CSF and serum samples are used and oligoclonal bands are revealed with IgG specific antibody staining. All laboratories performing isoelectric focusing should check their technique at least annually using "blind" standards for the five different CSF and serum patterns. Quantitative measurements of IgG production in the CNS are less sensitive than isoelectric focusing. The preferred method for detection of blood-CSF barrier dysfunction is the albumin quotient. The CSF albumin or total protein concentrations are less satisfactory. These results must be interpreted with reference to the age of the patient and the local method of determination. Cells should be counted. The normal value is no more than 4 cells/microliters. Among evolving optional tests, measurement of the combined local synthesis of antibodies against measles, rubella, and/or varicella zoster could represent a significant advance if it offers higher specificity (not sensitivity) for identifying chronic rather than acute inflammation. Other tests that may have useful correlations with clinical indices include those for oligoclonal free light chains, IgM, IgA, or myelin basic protein concentrations.

Flow rate of cerebrospinal fluid (CSF)--a concept common to normal blood-CSF barrier function and to dysfunction in neurological diseases

Many neurological diseases are accompanied by increased protein concentrations in the cerebrospinal fluid (CSF), described as a blood-CSF barrier dysfunction. The earlier interpretation as a "leakage" of the blood-CSF barrier for serum proteins could be revised by introduction of a "population variation coefficient" of the CSF/serum quotients for IgG, IgA and IgM (delta Q/Q) which is evaluated as a function of increasing albumin quotients (QAlb). The data presented here are based on specimens from 4380 neurological patients. These population variation coefficients were found to be constant over two orders of magnitude of normal and pathological CSF protein concentrations (QAlb = 1.6.10(-3)-150.10(-3)). This constancy indicates that there was no change in blood-CSF barrier related structures with respect to diffusion controlled protein transfer from blood into CSF and hence no change in molecular size dependent selectivity. The pathological increase of plasma protein concentrations in CSF in neurological diseases could also be explained quantitatively by a decrease of CSF flow rate due to its bifunctional influence on CSF protein concentration: reduced volume exchange, and as newly stated, increased molecular net flux into CSF without change of permeability coefficients. Again, on the basis of a changing CSF flow rate, the hyperbolic functions, which describe empirically the changing quotient ratios between proteins of different size (e.g. QIgG:QAlb) with increasing CSF protein content (QAlb) can likewise be derived from the laws of diffusion as the physiologically relevant description. The hyperbolic discrimination line between brain-derived and blood-derived protein fractions in CSF in the quotient diagrams for CSF diagnosis can be further improved on the basis of the large number of cases investigated. Other physiological and pathological aspects, such as high CSF protein values in the normal newborn, in spinal blockade, in meningeal inflammatory processes, CNS leukemia or polyradiculitis as well as animal species dependent variations can each be interpreted as due to a difference or change in the CSF flow rate.

Intrathecal synthesis of IgM and IgA in neurological diseases: comparison of two formulae with isoelectric focusing

The intrathecal IgM and IgA immune response was studied by detecting oligoclonal IgM and IgA bands in CSF and by determining both the IgM/IgA indices as well as the intrathecal production of IgM and IgA by the Reiber formula. A good correlation was found between the demonstration of oligoclonal IgM (r = 0.890) and IgA bands (r = 0.927) and the Reiber formula. Compared with the finding of oligoclonal IgM/IgA bands calculation of an intrathecal IgM/IgA synthesis by the Reiber formula was less sensitive (86%). In two out of 22 controls and in 12 of 19 patients with polyradiculitis IgM and IgA indices were elevated while the other evaluation methods were negative. Even though oligoclonal IgM and IgA bands are considered to be a useful diagnostic tool in detecting intrathecal synthesis of IgM and IgA, i.e. in meningoencephalitis or neuroborreliosis for clinical practice, the Reiber formula provides reliable results. Detection sensitivity of assays for CSF-IgM and -IgA should be at least 1.0 mg/l.

Comparison of seven formulae and isoelectrofocusing for determination of intrathecally produced IgG in neurological diseases

Seven different formulae and agarose isoelectrofocusing (AIF) using immunolabelling for IgG were compared for their ability to discriminate between intrathecally produced IgG and transudated IgG in cerebrospinal fluid. All reference limits were set to a specificity of 97.5% (reference group, n = 211). The probability of a positive test (p+) was evaluated for 112 patients with multiple sclerosis (MS), 42 with meningitis, 114 with noninflammatory diseases affecting the central nervous system (CNS), 23 with Guillain-Barré syndrome, and 56 with various diseases not affecting the CNS. Agarose isoelectrofocusing had the best diagnostic sensitivity (93%) for MS, combined with a low p+ (0-19%) for other diseases. Among the formulae, the IgG extended index and Reiber's hyperbolic formula were equivalent, giving high (75-79%) diagnostic sensitivity for MS combined with low p+ (4-22%) for other diseases. All other formulae, although sensitive for MS, had a higher rate of false positive results.