oligoclonal

Oligoclonal is an adjective used to describe a limited number of antibody-producing cell clones, resulting in a restricted repertoire of immunoglobulins. In immunology, oligoclonality sits between polyclonality (many different clones) and monoclonality (a single clone). Oligoclonality can occur in various tissues and fluids where local immune responses take place, including the central nervous system and bloodstream.

In clinical practice, the term often appears in relation to oligoclonal bands, which are discrete immunoglobulin G bands detected in cerebrospinal fluid (CSF) but not in serum. The presence of CSF-restricted oligoclonal bands indicates intrathecal IgG synthesis and is a common laboratory finding in inflammatory conditions of the CNS, most notably multiple sclerosis. However, oligoclonal bands are not specific to MS and can be seen in infections, autoimmune diseases, and other inflammatory states.

Detection relies on separation of proteins by electrophoresis or isoelectric focusing, followed by immunoblotting or immunofixation to reveal IgG bands. Patterns are typically described as four patterns: Pattern 1 (no bands in CSF), Pattern 2 (CSF-specific bands), Pattern 3 (CSF bands with additional serum bands), and Pattern 4 (bands identical in CSF and serum). Pattern 2 is the hallmark of intrathecal IgG synthesis, whereas patterns 1, 3, and 4 reflect different relationships between CSF and serum immunoglobulins.

Clinical interpretation requires context, repeat testing if needed, and correlation with imaging and other laboratory data to distinguish MS from other causes of CSF inflammation.