Determination of IgG subgroups in cerebrospinal fluid of multiple sclerosis patients and others

Induction of brain-infiltrating T-bet-expressing B cells in multiple sclerosis

Objective

Results from anti‐CD20 therapies demonstrate that B‐ and T‐cell interaction is a major driver of multiple sclerosis (MS). The local presence of B‐cell follicle‐like structures and oligoclonal bands in MS patients indicates that certain B cells infiltrate the central nervous system (CNS) to mediate pathology. Which peripheral triggers underlie the development of CNS‐infiltrating B cells is not fully understood.

Methods

Ex vivo flow cytometry was used to assess chemokine receptor profiles of B cells in blood, cerebrospinal fluid, meningeal, and brain tissues of MS patients (n = 10). Similar analyses were performed for distinct memory subsets in the blood of untreated and natalizumab‐treated MS patients (n = 38). To assess T‐bet(CXCR3)⁺ B‐cell differentiation, we cultured B cells from MS patients (n = 21) and healthy individuals (n = 34) under T helper 1‐ and TLR9‐inducing conditions. Their CNS transmigration capacity was confirmed using brain endothelial monolayers.

Results

CXC chemokine receptor 3 (CXCR3)‐expressing B cells were enriched in different CNS compartments of MS patients. Treatment with the clinically effective drug natalizumab prevented the recruitment of CXCR3^high IgG1⁺ subsets, corresponding to their increased ability to cross CNS barriers in vitro. Blocking of interferon‐γ (IFNγ) reduced the transmigration potential and antigen‐presenting function of these cells. IFNγ‐induced B cells from MS patients showed increased T‐bet expression and plasmablast development. Additional TLR9 triggering further upregulated T‐bet and CXCR3, and was essential for IgG1 switching.

Interpretation

This study demonstrates that T‐bet^high IgG1⁺ B cells are triggered by IFNγ and TLR9 signals, likely contributing to enhanced CXCR3‐mediated recruitment and local reactivity in the CNS of MS patients. ANN NEUROL 2019;86:264–278

Pro-inflammatory pattern of IgG1 Fc glycosylation in multiple sclerosis cerebrospinal fluid

BACKGROUND

Immunoglobulin G (IgG) effector functions are regulated by the composition of glycans attached to a conserved N-glycosylation site in the Fc part. Intrathecal production of IgG, especially IgG1, is a hallmark of multiple sclerosis (MS), but nothing is known about IgG Fc glycosylation in MS and in cerebrospinal fluid (CSF) in general.

METHODS

We applied mass spectrometry of tryptic Fc glycopeptides to analyze IgG Fc glycosylation (sialylation, galactosylation, fucosylation, and bisecting N-acetylglucosamine (GlcNAc)) in 48 paired CSF and serum samples from adult patients with MS or a first demyelinating event highly suggestive of MS (designated as MS cases), and from healthy volunteers and patients with other non-inflammatory diseases (control group). p values were adjusted for multiple testing.

RESULTS

Our experiments revealed four main results. First, IgG1 glycosylation patterns were different in CSF vs. serum, in the MS group and even in control donors without intrathecal IgG synthesis. Second, in MS patients vs. controls, IgG1 glycosylation patterns were altered in CSF, but not in serum. Specifically, in CSF from the MS group, bisecting GlcNAc were elevated, and afucosylation and galactosylation were reduced. Elevated bisecting GlcNAc and reduced galactosylation are known to enhance IgG effector functions. Third, hypothesis-free regression analysis revealed that alterations of afucosylation and bisecting GlcNAc in CSF from MS cases peaked 2-3 months after the last relapse. Fourth, CSF IgG1 glycosylation correlated with the degree of intrathecal IgG synthesis and CSF cell count.

CONCLUSIONS

The CNS compartment as well as the inflammatory milieu in MS affect IgG1 Fc glycosylation. In MS, the CSF IgG1 glycosylation has features that enhance Fc effector functions.

The effect of large-dose prednisone therapy on IgG subclasses in multiple sclerosis

The effect of large-dose prednisone therapy (3960 mg over 56 days) on IgG subclasses in the cerebrospinal fluid and sera, as well as on their intrathecal synthesis, was studied in 15 patients with clinically definite multiple sclerosis. The concentration of IgG subclasses was measured using ELISA with monoclonal antibodies against human IgG subclasses, secondary biotinylated antibody and avidin-biotin-peroxidase complex. There was a decrease of IgG1, IgG3 and IgG4 in the CSF of MS patients after the treatment, but the differences did not reach statistical significance. The IgG index was decreased about 34% (p < 0.01) after the therapy. This was mainly due to diminished synthesis of IgG1 and IgG3. The significance of IgG subclasses in the pathogenesis of MS is discussed.

Intrathecal synthesis of IgG subclasses in multiple sclerosis and in acquired immunodeficiency syndrome (AIDS)

Serum and cerebrospinal fluid (CSF) of 50 neurological patients (24 multiple sclerosis (MS), ten acquired immunodeficiency syndrome (AIDS) and 16 other neurological diseases (OND)) and ten controls were analyzed by enzyme-linked immunosorbent assay (ELISA) for IgG subclass quantification and for the calculation of intrathecal synthesis (ITS). Total IgG was determined by two methods: electroimmunodiffusion (EID) and ELISA. A highly significant correlation was established between both methods. The existence of ITS was proved by the IgG/albumin ratio, the IgG index, Tourtellotte's formula, and Schuller's formula. In AIDS patients all IgG subclasses showed an increase in the CSF, whereas in sera only the IgG1 was significantly increased. CSF of MS patients showed a predominant increase of IgG1 whereas no significant modification of IgG subclasses was observed in sera. In most of the AIDS patients there was an ITS of IgG1, IgG3 and IgG4, but rarely (3/10) IgG2. In contrast, a polyclonal ITS of IgG was exceptional (1/24) in MS patients. No significant correlation could be established between clinical data and IgG subclass ITS in MS. The variations of each IgG subclass in serum and in ITS were not significantly correlated. Measurement of each IgG subclass and calculation of ITS seems essential in order to analyze any subclass antibody repertory inside the central nervous system.

Identification of IgG subclasses' oligoclonal bands in multiple sclerosis CSF

IgG subclasses' oligoclonal bands in unconcentrated CSF from MS patients were detected by isoelectric focusing in agarose gel with subsequent immunoblotting using mouse monoclonal antibodies to human IgG subclasses and double-antibody avidin-biotin-alkaline phosphatase system. All MS CSF showed presence of oligoclonal bands specific to the IgG1 subclass; in addition, several of these samples also had oligoclonal bands specific to IgG3, IgG2, or IgG4, in order of decreasing frequency. Since the CSF of a greater number of MS patients showed oligoclonal bands specific to the IgG1 and IgG3 subclasses, the findings are consistent with those reported in patients with chronic viral infections and autoimmune diseases.

Total, anti-viral, and anti-myelin IgG subclass reactivity in inflammatory diseases of the central nervous system

Total IgG subclass levels, anti-viral, anti-myelin basic protein (anti-MBP), and anti-ganglioside 1 (anti-GM1) IgG subclass levels were measured in 6 patients with herpes simplex virus encephalitis (HSVE), 16 with borreliosis, 8 with other bacterial infections, 12 with multiple sclerosis (MS), 13 with subacute sclerosing panencephalitis (SSPE), 5 with glioblastoma and 12 controls. Total IgG1 levels were elevated in cerebrospinal fluid (CSF) from all patient groups (but not in the controls), IgG2 in bacterial infections, IgG3 in HSVE and borreliosis and IgG4 in some SSPE patients. The anti-viral (anti-measles, varicella zoster virus and rubella) IgG antibodies in MS were restricted to IgG1, anti-measles IgG to IgG1 and sometimes IgG4 in SSPE, anti-borrelia IgG to IgG1, IgG2 and IgG3. In contrast to anti-viral antibodies, anti-MBP and GM1 antibodies belonged to IgG1, IgG3 or IgG4 in MS. The nature of the immunological activation appears to be reflected in the subclass patterns elicited in the central nervous system. Different IgG subclass patterns in infectious diseases and MS suggest a difference between antigen-specific and non-specific B-cell activation.

Extended repertoire of specific antibodies in CSF of patients with subacute sclerosing panencephalitis compared to those with multiple sclerosis: anti-bacterial antibodies are also increased

Serum and cerebrospinal fluid (CSF) from eight patients with subacute sclerosing panencephalitis (SSPE), 21 with multiple sclerosis (MS) and 16 controls were analyzed for IgG subclass pattern of anti-viral and anti-bacterial antibodies. In CSF of SSPE and MS patients IgG1 and IgG4 antibodies to measles and IgG1 to mumps were increased compared to the controls. In addition, the SSPE patients had elevated levels of IgG1 to PPD, teichoic acid, and to dextran in CSF. The group of MS patients had decreased levels of IgG1 antibodies to Staphylococcus aureus alpha-toxin.

Immunoglobulin G in multiple sclerosis brain

We extracted free and bound IgG from plaques and normal-appearing white matter of multiple sclerosis (MS) brains. By isoelectric focusing (IEF), three patterns of IgG distribution were seen: (A) a restricted high-pI distribution with a specific band at low pH, (B) a restricted high-pI pattern, and (C) a broad pI pattern similar to that of the unbound IgG extracted at neutral pH. In one MS brain, we compared the IEF pattern of plaque material with that of normal-appearing white matter (NAWM); the low-pH extract of plaque material (PM) had a restricted pattern at high pI. In another MS brain, a specific band of bound IgG was found. These data suggest that MS lesions expose an antigen(s) unique to MS. B cells consequently might be stimulated by a disease-related antigen(s) in the MS lesion.

IgG1,3 and 4 oligoclonal bands in multiple sclerosis and other neurological diseases

Cerebrospinal fluid (CSF) samples from 10 patients with Multiple Sclerosis (MS) and 7 with other neurological diseases (OND) were studied in order to detect oligoclonal restriction of IgG subclasses 1,3 and 4. Agarose isoelectric focusing (AGA-IEF) followed by Western capillary blotting and immunoperoxidase staining with specific monoclonal antibodies were used. All MS samples showed oligoclonal IgG1 and 6 of them also had IgG3 or IgG4 bands. In the OND group only patients with subacute sclerosing panencephalitis (SSPE) and Guillain-Barré disease (GBD) showed CSF oligoclonal patterns for IgG subclasses. Our results demonstrate that in MS CSF other IgG subclasses beside IgG1 may display an oligoclonal pattern. The finding of more than one subclass in the same band indicates a microheterogeneous composition of these oligoclonal bands.

Imbalance in recruitment of IgG (Gm) allotype-producing B-cell subsets from blood to brain in multiple sclerosis

In Gm3/Gm3 homozygous multiple sclerosis (MS) patients, in vitro production of the G1m(3) allotype of IgG1 induced by the T-independent polyclonal B-cell activator Salmonella paratyphi B (SPB) was lower than that of normal individuals of the same Gm phenotype. In contrast, lymphocytes from Gm1/Gm3 heterozygous MS patients responded to the same stimulus with a significantly increased G1m(3) allotype synthesis not observed in normal individuals of the same phenotype. The high level of intrathecal IgG1 production observed in MS patients might be achieved by a selection at the blood-brain barrier of some peripheral T-independent B-cell clones which in Gm3/Gm3 homozygous would bear the G1m(3) allotype, hence a peripheral depletion of this subset, whereas in Gm1/Gm3 heterozygous a preferential admission of the G1m(1)-producing B-cells would lead to a preferential synthesis of this allotype in the central nervous system and to a relative increase of G1m(3) production by the remaining peripheral B cells.

[Cerebrospinal fluid proteins: III. Normal values of immunoglobulins G, A and M (variations related to race, sex and age)]

The literature on quantitation of immunoglobulins in normal CSF and variations of these values related to race, sex and age was reviewed. Immunoglobulins (Ig) G, A and M of normal CSF (sub-occipital puncture) of 116, 78 and 45 patients respectively, were measured by radial immunodiffusion, in order to verify variations related to race, sex and age, as well as to establish their normal limits. The results allowed us to conclude that: a) there are no differences between races with respect to the levels of IgG, A and M; b) variations related to sex or age on the CFS immunoglobulins content in children (1 to 11 years old) are not found; c) the mean IgG (mg/100 ml) level in children is lower than in adults, although the mean IgG percentage concentration in children is not different from that found in adults; the normal range for CSF IgG in children is 0.21 to 2.93 mg/100 ml; d) the mean IgA content (mg/100 ml and % of the total protein) in children are lower than in adults and in physiological conditions do not exceed 0.15 mg/100 ml (0.7% of the total protein); e) there are no differences related to sex or age with respect to the CSF levels of immunoglobulins in adults; the normal range of IgG in adults is 0.51 to 4.00 mg/100 ml; in children and adults the normal limits for the relative values of IgG are 3 to 12%; IgA is found in the CFS of adults in a concentration up to 0.32 mg/100 ml (0.9%); f) IgM is found in both children's and adults' CSF at very low levels, not exceeding 0.2 mg/100 ml (0.25%). Comparison of the results obtained in this work with those found in some publications was carried out and is briefly discussed.

Nitrocellulose immunofixation following agarose electrophoresis in the study of immunoglobulin G subgroups in unconcentrated cerebrospinal fluid

A method is presented which enables the study of cerebrospinal fluid proteins in minimal volumes of unconcentrated fluid. The method involves agarose electrophoresis followed by transfer of the proteins to a nitrocellulose membrane and then demonstration of their distribution using a double-antibody immunoperoxidase technique. The method is used here for the study of immunoglobulin G and its subgroups, and clearly shows that the oligoclonal pattern observed in multiple sclerosis is not restricted to any one subgroup.

[Cerebrospinal fluid G immunoglobulins in nervous system diseases]

Cerebrospinal fluid IGG and the relations with total protein, and with prealbumin + albumin and the IGG index were studied in 160 patients with various neurological disorders. These patients were distributed in 8 groups according to diagnosis as follows: inflammatory (21 cases); demyelinating (31 cases); degenerative (10 cases); cerebrovascular (19 cases); tumoral (3 cases); convulsive (20 cases); headache (11 cases); other neurological disorders (45 cases). According to the results (table 1) the best applicability of IGG study is the group of chronic inflammatory diseases (neurosyphilis and neurocysticercosis) and the demyelinating disorders (multiple sclerosis). Emphasis is given to the possibility of the occurrence of local synthesis of IGG in the central nervous system in these 2 groups.