B-cells contain specific areas (genes) in their that code for the production of antibodies (also known as ). The immunoglobulin genes consist of numerous, discontinuous coding segments. As B-cells develop and mature, these DNA segments are rearranged in a controlled fashion such that each mature B-cell has a unique rearrangement profile. When the body is exposed to , such as or , the B-cell immunoglobulin genes undergo a permanent rearrangement in order to produce antibodies directed against that threat. For instance, if a person is exposed to a rubella virus, then some of the B-cells change and become rubella antibody-secreting cells. If a person is exposed to a hepatitis B virus, then some of the B-cells become hepatitis B antibody-secreting cells.
The body maintains a library of antibody "blueprints" so that the next time it is exposed to a threat, it can use the B-cell blueprint to rapidly produce large quantities of a specific antibody. This means that the population of mature B-cells is normally diverse (polyclonal) with small amounts of many different kinds of antibodies and temporary increases in specific antibodies as needed to counter an exposure. In this setting, B-cell expansions are polyclonal, with each clone containing relatively few cells and no one clone predominating.
With a B-cell lymphoma, an abnormal B-cell is formed and begins to clone itself. The identical, cloned (monoclonal) cells do not function normally, their replication is not controlled by the , and they may not die as normal cells do. A cancerous monoclonal population of B-cells accumulates, begins to crowd out normal cells, and may eventually spread through the and blood to other lymph nodes or tissue, including .
All of the monoclonal B-cells produced will have an identical immunoglobulin gene rearrangement profile. The neoplastic clones are generally large, and therefore the clonal cells are the predominant B-cells present in involved tissue (e.g., lymph node, bone marrow, blood, body fluid). Detection of a predominant immunoglobulin gene rearrangement profile often indicates the presence of a neoplastic B-cell population. This can help establish the diagnosis of a B-cell lymphoma or evaluate for residual or recurrent disease after treatment.