Intrathecal IgG synthesis in multiple sclerosis: comparison between isoelectric focusing and quantitative estimation of cerebrospinal fluid IgG

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.

Correlation of the IgG index and oligoclonal bands in the cerebrospinal fluid of patients with multiple sclerosis

AIMS

The aim of this study was to assess the correlation between IgG index values and the number of the oligoclonal IgG bands (OCB) in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS).

MATERIAL AND METHODS

The set of 150 patients consisted of 41 males and 109 females (aged 18-68, mean 36.6 +/- 10.1 years). The CSF collected by a lumbar puncture was examined evaluating intrathecal synthesis using the IgG index and determining OCB. The number of alkaline OCB in the CSF was assessed using the method of isoelectric focusing. Pearson's correlation analysis, and homogeneity chi(2) test, Mann-Whitney test, paired-sample t-test (parametric) and Wilcoxon signed-ranks test (nonparametric) were used to evaluate the statistical significance of the results.

RESULTS

No positive correlation between the IgG index and the number of OCB was found. Mann-Whitney test also failed to demonstrate any significant difference of the IgG index values in patients both with the OCB number > or = 2 and < 2.

CONCLUSION

This study did not confirm any correlation between the IgG index values and the OCB number in the CSF of MS patients.

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.

Laboratory investigation of cerebrospinal fluid proteins

Analysis of CSF proteins is useful in the diagnosis and management of neurological diseases in the following situations: 1. In inflammatory conditions when there is breakdown of blood-CSF barrier integrity. Meningitis is a medical emergency, with CSF total protein measurement being only a screening test. 2. In the detection of immune responses within the CNS. This is by far the most important application in a routine clinical setting, as it is now a firmly established criterion in the diagnosis of multiple sclerosis. Oligoclonal bands restricted to the CSF are the only reliable indicators of intrathecal immunoglobulin G synthesis and are practically always associated with inflammatory disease of the CNS. The method fo choice for detecting oligoclonal bands is isoelectric focusing with immunofixation. Quantitative measurement of IgG in the CSF is of no value in diagnostic pathology. 3. In destructive brain diseases when brain-specific proteins are released into the CSF, measurement of these proteins can give prognostic information.

Intrathecal Ig synthesis. Its detection by isoelectric focusing and IgG index

In a retrospective study on 999 patients, the likelihood ratios of the IgG index, Tourtellotte formula and IgG concentration in CSF and in serum, the albumin concentration in CSF and in serum, and the total protein in CSF, were compared in predicting intrathecal Ig synthesis. This synthesis was detected with isoelectric focusing (IEF). No patient was included more than once in the data collection. All patients with high IgG and other abnormalities in serum, as well as all xanthochromic and blood-tinged CSF specimens, were excluded from the study. Construction of ROC curves established that the IgG index, Tourtellotte formula and CSF IgG yield the same information: these parameters indicate the presence of intrathecal IgG synthesis. The likelihood ratio for the IgG index at a cut-off point of 0.80 for a positive test is 20; at a cut-off point of 0.5 for a negative test it is 5. For the Tourtellotte formula, it was found that the likelihood ratio reached a maximal value of 7 at a cut-off value of synthesis of 10 mg/day for a positive test. For a negative result, the formula had a likelihood ratio of 6 at a cut-off value of -5. For CSF IgG, it was found that the likelihood ratio was 4 for a positive test with a cut-off value of 0.1 g/l. For a negative outcome, the determination of CSF IgG is only meaningful at a very low cut-off value (0.03 g/l). The other parameters studied (serum IgG concentration, albumin concentration in CSF and in serum, and total protein in CSF) showed a likelihood ratio equal to 1. It is concluded that only the IgG index, the Tourtellotte formula and the CSF IgG concentration have predictive value for intrathecal Ig synthesis as recorded with IEF.

Oligoclonal "fingerprint" of CSF IgG in multiple sclerosis patients is not modified following intrathecal administration of natural beta-interferon

The IgG pattern in CSF was studied in 11 patients with multiple sclerosis who exhibited an oligoclonal banding upon thin-layer polyacrylamide gel isoelectric focusing followed by silver stain of unconcentrated CSF. Each patient received beta-interferon intrathecally during a 2 month period. No modification was observed over a 6 month period. In addition, the oligoclonal pattern was remarkably unique for each individual representing a typical "fingerprint" which allowed the identification of any single CSF.

Blood-cerebrospinal fluid barrier permeability to serum IgG subfractions and measurement of intrathecal IgG synthesis

CSF/serum gradients of IgG subfractions separated by isoelectric focusing (IF) have been measured by high resolving laser densitometry. In patients with normal blood-CSF barrier permeability (N.25) and with barrier damage due to acute idiopathic polyneuropathy (N.15) and to medullary compression (N.17), the CSF/serum gradients of IgG subfractions were negatively correlated with their pI. This electrostatic selectivity appeared to be reverted in barrier damage due to acute meningoencephalitis (N.15). In a series of multiple sclerosis patients (N.31), the CSF/serum gradients of IgG subfractions lacking CSF oligoclonal bands have been used to assess the overall barrier permeability to serum IgG. All intra-BCB synthesized IgG subfractions could be measured by densitometry, whereas with other quantitative formulae, 23-26% of the results were false negatives; the total intrathecal IgG amount ranged from 0.01 to 11 mg/dl. The most frequent and prominent fractions appeared to be cathodic. Electrostatic and steric barrier selectivity must be taken into account when the amount of intrathecal IgG synthesis has to be measured.

Suspected and clinically definite multiple sclerosis: the relationship between CSF immunoglobulins and clinical course

CSF immunoglobulins were examined in 103 patients with clinically definite multiple sclerosis, 106 patients with either suspected or progressive possible multiple sclerosis and 72 patients with other neurological diseases. Raised CSF IgG index and oligoclonal banding were found in 71% and 75% of clinically definite multiple sclerosis patients respectively and both tests were abnormal in 11% of patients with other neurological diseases. The CSF IgG index and the presence of oligoclonal IgG did not relate to the severity or duration of established disease in these patients. In patients with suspected and progressive possible multiple sclerosis, both a raised IgG index and the presence of oligoclonal banding were found significantly more frequently than in the OND group. Abnormalities of these parameters were significantly correlated with the presence of an abnormal evoked response in these patients (chi 2 = 10.16 p less than 0.01). When 47 patients with suspected multiple sclerosis were studied prospectively the presence of oligoclonal banding at presentation was associated with development of further disease activity.

Cerebrospinal fluid in multiple sclerosis: relationships between immunoglobulins, leucocytes and clinical features

Cerebrospinal fluid (CSF) from 120 patients with multiple sclerosis was analyzed by polyacrylamide gel electrophoresis, as well as routine laboratory microscopy and assays of total protein and immunoglobulin G (IgG). Negative correlations were found between leucocyte counts and patient age, duration of disease and time from last clinical relapse. There was a positive correlation between the leucocyte count and amount of gammaglobulin. A correlation between gammaglobulin content and degree of disability was found. With increasing duration, the gammaglobulin concentration rose only if there was increasing disability. In terms of correlations with clinical features, differences existed depending on whether IgG was assayed immunologically or by electrophoresis and densitometry. Evidence of increased blood: CSF barrier permeability (transudation of high molecular weight proteins) was found in patients with progressive disease. The presence of oligoclonal bands was the CSF abnormality most frequently encountered.

The basis of intra-blood-brain-barrier IgG synthesis

We hold that the intra-blood-brain-barrier (BBB) IgG synthesis (SYN) rate can be quantitated reliably and validly. Although several formulas distinguish patients with multiple sclerosis from normal controls equally well, only the SYN rate formula has been validated in humans using isotopic tracer techniques. Our formula for the IgG SYN rate is reducible to Reiber's formula; therefore, both can be used to quantify the IgG SYN rate in a manner not possible using the IgG index. Although our SYN rate formula has been validated for a modest range of BBB abnormalities (cerebrospinal fluid/serum albumin ratios), there is evidence to suggest that it may be used even in patients having severe BBB damage. We question the acceptance of unique cerebrospinal fluid IgG bands as indisputable evidence of intra-BBB IgG SYN in the presence of a modest to severely damaged BBB. Finally, the utility of quantitation and detection of intra-BBB IgG SYN by standardized methods in a group of asymptomatic, normal individuals compared with a group of patients with clinical definite multiple sclerosis is presented.

Acute changes in blood-CSF barrier permselectivity to serum proteins after intrathecal methotrexate and CNS irradiation

Ten children affected by acute lymphoblastic leukaemia without CNS involvement were treated with a CNS prophylaxis protocol. Intrathecal methotrexate and CNS irradiation (60Co) administered at different times both induced an increase in blood-CSF barrier permeability to serum proteins (albumin, IgG, alpha 2 macroglobulin). The relationship between permeability coefficients of proteins was analysed by theoretical porous or vesicular blood-CSF barrier models. The analysis indicated that both therapeutic procedures affect endothelial pinocytosis. An increase in radius of pinocytotic vesicles from 400 to 1500 A seemed the most relevant change. The damage of endothelial barrier permselectivity could be involved in acute and late delayed toxic effects of intrathecal methotrexate and of CNS irradiation.

CFS oligoclonal bands in MS and other neurological diseases detected by agarose isoelectric focusing and electrophoresis

Agarose gel isoelectric focusing (IEF) and electrophoresis (EF) were compared for detection of CSF oligoclonal bands in multiple sclerosis (MS) and other neurological diseases. The CSF IgG/albumin ratio, the IgG-Index and the IgG synthesis per day in the CNS were also considered. IEF was highly sensitive, revealing oligoclonal bands in 100% of CSF from 40 clinically definite MS, while EF had a sensitivity of 70%. In 90 patients with other neurological diseases, IEF revealed oligoclonal bands in 25.5%, EF in 11.1%. The IgG-index was the most sensitive of the quantitative parameters.

Isoelectric focusing of CSF proteins and the future evolution of multiple sclerosis: a clinical follow-up

A clinical follow-up covering a period of 5-10 years after onset was performed in 150 patients with optic neuritis or other potential onset symptoms of MS. Thin-layer isoelectric focusing had been used for the initial CSF-protein analysis. No evidence for a more probable alternative diagnosis appeared in 147 patients while a non-MS diagnosis was established in 3 patients. Among these 147 subjects the planned follow-up was accomplished in 131 patients, but not in 16. An evolution into clinically definite MS occurred in 59 subjects, in whom oligoclonal CSF immunoglobulin was found in 92%. Further clinical activity without spatial dissemination--i.e. lesser degrees of diagnostic probability for MS--were found in 35 patients in whom oligoclonal CSF immunoglobulin components were detected in 86%. Among the 131 patients with a complete follow-up, 45 remained free from further clinical activity; oligoclonal CSF immunoglobulin components occurred in 40% of these patients. The frequency of further clinical activity with or without spatial dissemination was significantly higher in subjects exhibiting oligoclonal CSF immunoglobulin components than in those without such changes.

On the diagnostic value of different CSF investigations in multiple sclerosis

An assessment was made of the relative values of different methods of calculating intrathecal IgG synthesis in multiple sclerosis. In 60 patients with definite, probable or possible multiple sclerosis the IgG/protein and IgG/albumin ratios, the IgG index, the Tourtellotte formula and the graphic evaluation according to Reiber were applied. All the patients had oligoclonal IgG in the CSF. Reiber's method was the most sensitive, yielding 66% of abnormal findings. Only the cell count showed significant differences between active and inactive stages. There was a correlation between the cell count and the daily rate of intrathecal IgG synthesis and between the latter and the number of oligoclonal bands in CSF, but none of these parameters correlated with duration of disease or the number of previous bouts.

Heterogeneous models for blood-cerebrospinal fluid barrier permeability to serum proteins in normal and abnormal cerebrospinal fluid/serum protein concentration gradients

Cerebrospinal fluid (CSF)/serum concentration gradients (Q) of individual proteins (albumin, IgG, alpha 2-macroglobulin) have been studied in controls and in patients in whom the lumbar CSF flow is altered (medullary compression) or the blood-CSF barrier (BCB) function impaired (acute idiopathic polyneuropathy and acute meningoencephalitis). The analysis of relationships among protein Q has been performed by total and multiple regressions and the actual BCB permeability to individual proteins has been interpreted according to the accepted theoretical porous or vesicular BCB models. The exponential Q-IgG vs. Q-albumin total regression, and the poor Q-alpha 2-macroglobulin vs. Q-albumin regression found in controls, together with the different multiple regressions among proteins and the high Q-IgG vs. Q-albumin partial regression coefficients found in medullary compression, acute idiopathic polyneuropathy and acute meningoencephalitis, indicated that different permeability mechanisms can be postulated. Heterogeneous, fairly independent permeability BCB mechanisms maintain the normal CSF/serum protein concentration gradient. Pinocytotic vesicles or pores of radius exceeding 1000-1500 A, probably located at the capillary endothelium, account for the main serum-derived CSF protein fraction(s) with large hydrodynamic radius (R). A more selective endothelial vesicular transport with a radius of 250 A transfers a negligible amount of protein from serum into CSF. Proteins with small R also enter the CSF through a set of selective pores of radius 120 A, probably at the level of the choroidal epithelium. Pinocytotic vesicles with a radius of 250 A and increased rate of formation induce the accumulation of proteins below an obstruction of lumbar CSF flow. An increased formation rate of vesicles with a radius of 450 A can explain the increased capillary permeability in nerve roots in acute idiopathic polyneuropathy. Loss of selectivity was the main feature of BCB in acute meningoencephalitis, and it seemed to be due to pores or vesicles with a radius larger than 1000-1500 A. The heterogeneity of BCB mechanisms must be taken into account when the intrathecal synthesis of a protein, also derived from serum (for example IgG), has to be measured.

Assessment of cerebrospinal fluid immunoglobulin patterns after isoelectric focusing. Use of kappa and lambda light chain immunoperoxidase staining

Assessment of the presence of immunoglobulin (Ig) of restricted heterogeneity i.e. oligoclonal Ig in cerebrospinal fluid subjected to isoelectric focusing (IEF) may be difficult because of the tendency of the technique to subdivide even normal polyclonal IgG into bands and zones. Focused Ig stained by the immunoperoxidase technique for kappa and lambda light chains shows correspondence between the two patterns in the case of normal polyclonal Ig, but a marked discrepancy between kappa and lambda patterns in disorders associated with oligoclonal Ig, and kappa and lambda immunofixation makes assessment of agarose IEF separations of IgG more reliable.

Identification of the kappa and lambda light chains within the CSF immunoglobulin region in multiple sclerosis and subacute sclerosing panencephalitis by immunofixation after isoelectric focusing

The distribution of the kappa and lambda light chains within the cerebrospinal fluid (CSF) IgG oligoclonal bands of 15 multiple sclerosis (MS) and 3 subacute sclerosing panencephalitis (SSPE) patients has been studied by isoelectric focusing (IF) followed by direct immunofixation. The oligoclonal bands demonstrated by IF were both homogeneous and heterogeneous with regard to the light chain type; in the MS patients there was a prevalence of heterogeneous bands and of homogeneous bands of lambda type, while in SSPE a slight prevalence of kappa homogeneous bands was found. The kappa homogeneous bands were preferentially disposed in a more cathodal position in respect to lambda IgG bands; in some cases bands probably constituted only of free light chains of lambda type were found. Finally, in some cases, the oligoclonal IgG pattern was more distinct after immunofixation than after basal IF.