The oligoclonal bands consist of immunoglobulins secreted by plasma cells (B cells). They are called oligoclonal because there are several clones of B-cells secreting them; when they are only present in CSF, it´s assumed that they have been produced inside the central nervous system (CNS); if they are also present in serum (mirror pattern), they are not specific of CNS, so they are produced outside (CNS is separated from the rest of the body by different barriers). The presense of oligoclonal bands only in CSF confirms, in the appropriate cinical situation, multiple sclerosis, but they are not specific of this disease.

A monoclonal band is an immunoglobulin secreted by a single clone of B-cells (a clone is the set of cells deriving from one single cell, all producing the same immunoglobulin when applied to B-cells)