A technique for the elution of cell-surface antibody from human brain tissue

Intruders or protectors - the multifaceted role of B cells in CNS disorders

B lymphocytes are immune cells studied predominantly in the context of peripheral humoral immune responses against pathogens. Evidence has been accumulating in recent years on the diversity of immunomodulatory functions that B cells undertake, with particular relevance for pathologies of the central nervous system (CNS). This review summarizes current knowledge on B cell populations, localization, infiltration mechanisms, and function in the CNS and associated tissues. Acute and chronic neurodegenerative pathologies are examined in order to explore the complex, and sometimes conflicting, effects that B cells can have in each context, with implications for disease progression and treatment outcomes. Additional factors such as aging modulate the proportions and function of B cell subpopulations over time and are also discussed in the context of neuroinflammatory response and disease susceptibility. A better understanding of the multifactorial role of B cell populations in the CNS may ultimately lead to innovative therapeutic strategies for a variety of neurological conditions.

The Role of Antibodies in the Pathogenesis of Multiple Sclerosis

The presence of persistent intrathecal oligoclonal immunoglobulin G (IgG) bands (OCBs) and lesional IgG deposition are seminal features of multiple sclerosis (MS) disease pathology. Despite extensive investigations, the role of antibodies, the products of mature CD19⁺ B cells, in disease development is still controversial and under significant debate. Recent success of B cell depletion therapies has revealed that CD20⁺ B cells contribute to MS pathogenesis via both antigen-presentation and T-cell-regulation. However, the limited efficacy of CD20⁺ B cell depletion therapies for the treatment of progressive MS indicates that additional mechanisms are involved. In this review, we present findings suggesting a potential pathological role for increased intrathecal IgGs, the relation of circulating antibodies to intrathecal IgGs, and the selective elevation of IgG1 and IgG3 subclasses in MS. We propose a working hypothesis that circulating B cells and antibodies contribute significantly to intrathecal IgGs, thereby exerting primary and pathogenic effects in MS development. Increased levels of IgG1 and IgG3 antibodies induce potent antibody-mediated cytotoxicity to central nervous system (CNS) cells and/or reduce the threshold required for antigen-driven antibody clustering leading to optimal activation of immune responses. Direct proof of the pathogenic roles of antibodies in MS may provide opportunities for novel blood biomarker identification as well as strategies for the development of effective therapeutic interventions.

The Bacterial Enzyme IdeS Cleaves the IgG-Type of B Cell Receptor (BCR), Abolishes BCR-Mediated Cell Signaling, and Inhibits Memory B Cell Activation

Ag binding to the BCR is a critical step in B cell development and activation, initiating a cascade of signaling events ultimately leading to proliferation, differentiation, or cell death. A bacterial enzyme, IgG-degrading enzyme of Streptococcus pyogenes (IdeS), was shown to specifically cleave IgG molecules below the hinge region of soluble IgG and when IgG is bound to Ag, resulting in one F(ab')2 molecule and one homodimeric Fc fragment. Whether IdeS could also cleave the IgG molecule when it is present in the BCR attached to the B cell membrane in a complex with CD79a and CD79b is unknown. In this article, we present human in vitro and ex vivo data showing that IdeS cleaves the IgG present in the BCR complex and very efficiently blocks Ag binding to the BCR. As a consequence of IdeS cleaving the BCR, signaling cascades downstream of the BCR are blocked, and memory B cells are temporarily silenced, preventing them from responding to antigenic stimulation and their transition into Ab-producing cells.

Autoantibodies to myelin basic protein within multiple sclerosis central nervous system tissue

Previous research has demonstrated that free (F) and bound (B) anti-myelin basic protein (anti-MBP) can be detected in the cerebrospinal fluid (CSF) of patients with active multiple sclerosis (MS). The purpose of this report was to determine whether the immunoglobulin G (IgG) isolated from central nervous system (CNS) tissue of MS patients contains anti-MBP. IgG was detected in free and bound hydrosoluble protein extracts obtained from the brain, spinal cord and optic nerves of a patient with clinically definite and neuropathologically confirmed MS. IgG was purified from free protein extracts from brain and spinal cord by Protein G-Sepharose affinity chromatography. Anti-MBP was detected by a solid phase radioimmunoassay (RIA) in all free and bound protein extracts. Anti-MBP was isolated from purified IgG from brain and spinal cord by MBP-Sepharose affinity chromatography. Free anti-MBP in the context of whole protein extracts, within purified IgG or as purified antibody as well as tissue-bound anti-MBP in the context of whole protein extracts was completely neutralized by human MBP (h-MBP) and synthetic peptide No. 56 (residues 75-95 of h-MBP) and did not react with synthetic peptide No. 41 (residues 35-58 of h-MBP). Anti-MBP which has previously been detected in the CSF of MS patients with active disease is also present as free antibody in the extracellular space of MS-central nervous system tissue and in a smaller proportion as tissue-bound antibody.

Increased synthetic peptide specificity of tissue-CSF bound anti-MBP in multiple sclerosis

Free and bound hydrosoluble protein extracts were prepared from four anatomical areas of a multiple sclerosis (MS) cerebrum and from corresponding anatomical areas of a normal (non-MS) control. Increased levels of IgG and anti-myelin basic protein antibodies (anti-MBP) were detected in all MS samples and they were undetectable in the controls. IgG and anti-MBP from free (unbound) hydrosoluble protein extracts are defined as free IgG and free anti-MBP while IgG and anti-MBP from tissue bound protein extracts are defined as bound IgG and bound anti-MBP. IgG was purified from free protein extracts by protein G Sepharose affinity chromatography and anti-MBP was further isolated from purified IgG by antigen specific (MBP) Sepharose affinity chromatography. Free and bound anti-MBP were reacted with 20 synthetic peptides of human MBP prepared by the Fmoc method. Free anti-MBP, whether in the context of whole protein extracts, or as purified IgG or as purified antibody was completely neutralized by peptides #12, #15, #56 and #56* containing overall residues 75-106, partially neutralized by peptides #27, #16 and #21 containing overall residues 61-83 and did not react with the remaining 13 peptides. Tissue bound anti-MBP was completely neutralized only by peptides #12, #15, #56 and #56* (overall residues 75-106) and showed no reactivity towards the remaining 16 peptides including peptides #27, #16 and #21. Synthetic peptide specificity of free anti-MBP purified from MS cerebrum was identical to previously reported specificity of free anti-MBP from MS cerebrospinal fluid (CSF), while tissue bound anti-MBP, as well as bound anti-MBP from CSF had a more restricted synthetic peptide specificity than free anti-MBP. This suggests that the most likely epitope of anti-MBP is located between residues 84 and 95 of human MBP just proximal to the tri-proline sequence (99-101).

Immunocomplexes in rat and rabbit spinal cord after injury

The possibility that, following a major lesion of the central nervous system, a humoral immune response could be evoked with formation of immune complexes "in situ" was investigated. For this purpose, an immunohistochemical study on rabbit and rat spinal cord at different times after surgical transection was carried out. The peroxidase-antiperoxidase method showed IgG decoration of the myelin sheaths starting a short time after surgery. The sera of intact and injured animals were then tested both by immunohistochemical methods on intact spinal cord sections and by immunoelectrophoresis on a protein extract of homologous spinal cord. The results showed in the rabbit the absence of antibodies to neural antigens before surgical injury and its appearance within a few days after surgery. On the other hand, in the rat, even before the injury, we found antibodies to neural tissue which decreased in the first few hours after injury, and returned to control values during successive days. The same experiments were conducted after a peripheral nerve lesion (sciatic nerve crush), but no immune response could be detected. The possible role of this immune response in the failure of axonal regeneration in mammalian spinal cord is briefly discussed.

Bound antibody in multiple sclerosis brains

Autopsy tissues of white and grey matter from brains of MS patients and controls were homogenized in PBS and centrifuged at 100,000 x g for 1 h. The residues were thoroughly washed with PBS and further extracted at acidic and alkaline pH. The eluates contained a low but significant amount of IgG, indicating that bound IgG was present in MS brains. A greater yield of IgG was obtained with alkaline pH buffer than with acidic pH buffer. In contrast, sections from 2 of 3 neurologic controls and 3 of 4 non-neurologic control failed to show detectable level of bound IgG extractable at acidic pH. These results might suggest the presence of antigen-antibody complexes in MS brains. Isoelectric focusing analysis demonstrated oligoclonal IgG bands in low pH eluates from MS brains and these bands were partly similar to those seen in neutral (unbound) pH brain extracts.

Isoelectric focusing of IgG eluted from multiple sclerosis and subacute sclerosing panencephalitis brains

Elevated IgG distributed in oligoclonal bands is characteristically observed in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS) or subacute sclerosing panencephalitis (SSPE). Similarly, IgG in bands has been detected in neutral saline (NS) and acid eluates of brain material from these two diseases. We have now used isoelectric focusing (IEF) to compare IgG eluted from control brain, three plaques and a white matter pool of an MS brain, and three regions of an SSPE brain. A direct peroxidase-conjugated anti-human IgG staining technique was used to stain IgG exclusively and to visualize the minute amounts of IgG obtained from individual MS plaques. Eluates from individual MS plaques have distinct IgG patterns; in contrast, those from separate SSPE brain areas have essentially identical IgG patterns. The identical IgG patterns in three areas of SSPE brain suggest a common response to the same antigen. The different IgG patterns among MS plaques suggest: (1) variable response to the same 'MS antigen' in each plaque, (2) response to different MS antigens in different plaques, (3) synthesis of 'nonsense' antibodies irrelevant to the pathogenesis of MS in each plaque, or (4) some combination of the above.

Immunoglobulin elution from multiple sclerosis brain

Immunoglobulin (Ig) was eluted from multiple sclerosis (MS) brain tissue. Razor thin slices of white matter from 10 g of MS and control brains were washed with 5 liters of phosphate-buffered saline (PBS), then treated for 90 sec with acetic acid, pH 2.5, containing Pepstatin and epsilon-aminocaproic acid. The protein concentrations of the PBS washes and neutralized acid eluates were determined, and the eluates were assayed for Ig by competitive microradioimmunoassay using rabbit anti-human F(ab1)2. Successive PBS washes reduced extracellular protein to a very low level. Equivalent quantities of protein were recovered from 7 MS and 6 non-MS brain samples after PBS washing and acetic acid elution. However, the amount of protein needed for 50% inhibition of [125I]IgG binding to anti-human F(ab1)2 was significantly less in MS brain than in non-MS brain (P less 0.05). The Ig in brain eluates was present in the void volume of a DEAE cellulose column. The techniques described above facilitate the isolation and characterization of cell-surface Ig in MS brain.