Multiple Sclerosis (MS) is a chronic neurological condition impacting the central nervous system, including the brain, spinal cord, and optic nerves. This disease involves inflammation, demyelination, and axonal degeneration, leading to various symptoms. Diagnosing MS is complex due to symptom and test result overlap with other conditions. Diagnosis typically involves clinical assessments, imaging studies like MRI, and laboratory evaluations. Biomarkers play a role in understanding and diagnosing diseases like MS, offering a more complete picture of the disease’s presence.
What Are IgG Antibodies?
Antibodies are proteins produced by the immune system to identify and neutralize foreign invaders like bacteria and viruses. Immunoglobulin G (IgG) is the most abundant type of antibody, making up about 75% of all serum antibodies. IgG antibodies are found in the blood and other extracellular fluids, protecting various body tissues from infection.
IgG antibodies are important in the body’s secondary immune response, occurring when the body encounters a pathogen it has previously fought. These antibodies neutralize pathogens by binding to their surface, preventing them from entering cells. They can also coat pathogens, signaling other immune cells to destroy them. IgG is unique because it can cross the placenta, providing a developing fetus with passive immunity.
IgG and Multiple Sclerosis
In Multiple Sclerosis, the immune system mistakenly attacks the myelin sheath, the protective covering around nerve fibers in the central nervous system. This autoimmune attack leads to inflammation and damage within the brain and spinal cord. A key feature of MS is the production of antibodies directly within the central nervous system, known as intrathecal IgG synthesis.
Intrathecal IgG synthesis is identified by two indicators: oligoclonal bands (OCBs) and an elevated IgG index. OCBs are distinct bands of IgG proteins found in the cerebrospinal fluid (CSF) but not in the blood, indicating localized immune activity. The IgG index is a quantitative measure comparing IgG in the CSF to IgG in the blood, adjusted for the blood-brain barrier’s integrity. Both OCBs and an elevated IgG index reflect the immune response occurring in the central nervous system of individuals with MS.
Testing IgG Levels for MS
Measuring IgG levels for MS involves a lumbar puncture, also known as a spinal tap, to collect cerebrospinal fluid (CSF). A small needle is inserted into the lower back to withdraw a CSF sample, the fluid surrounding the brain and spinal cord. CSF is preferred over blood because it directly reflects immune activity within the central nervous system.
Once collected, the CSF sample undergoes laboratory analysis for specific immune markers. The main tests are for oligoclonal bands (OCBs) and the IgG index. OCBs are identified by separating proteins based on their electrical charge. The IgG index compares the ratio of IgG to albumin in the CSF with the same ratio in a blood serum sample. These tests provide objective evidence of an immune response within the central nervous system, supporting an MS diagnosis.
Interpreting Test Results
Interpreting IgG test results for Multiple Sclerosis involves looking for specific patterns in the cerebrospinal fluid (CSF). The presence of two or more distinct oligoclonal bands (OCBs) in the CSF, not present in a corresponding blood sample, suggests MS. These bands indicate immune cells within the central nervous system are producing specific IgG antibodies. This finding is observed in most MS patients.
An elevated IgG index also indicates increased IgG production within the central nervous system. This quantitative measure confirms localized immune activity. While these findings are indicators, they are not used in isolation to diagnose MS. A neurologist integrates these lab results with clinical symptoms, neurological examination findings, and MRI scans of the brain and spinal cord for a comprehensive diagnosis. Elevated CSF IgG or OCBs can be present in other neurological conditions, requiring thorough evaluation by a specialist to differentiate MS.
The Role of IgG in Monitoring MS
While IgG levels, specifically oligoclonal bands (OCBs) and the IgG index, are valuable for initial MS diagnosis, they are not primary tools for ongoing monitoring of disease progression or treatment effectiveness. OCBs, once detected, remain stable over time in most MS patients, meaning they do not fluctuate with changes in disease activity or response to therapy. Similarly, an elevated IgG index indicates intrathecal IgG synthesis, but its levels do not consistently correlate with symptom fluctuations or treatment effectiveness.
For monitoring MS activity and treatment response, clinical assessments, such as evaluating changes in neurological function and symptom severity, are the main methods. Regular MRI scans of the brain and spinal cord track new lesions or changes in existing ones, providing objective evidence of disease activity. Other neurological tests may also assess specific functions. Thus, while IgG markers help establish an MS diagnosis, they offer limited utility in tracking the disease’s course or the impact of interventions after diagnosis.