B cell activation and plasma cell development
Immature B cells travel from the bone marrow through the bloodstream to lymphoid tissues, such as lymph nodes, where they are exposed to antigens. Antigens activate immature B cells.
Helper T-cells (which trigger and direct the immune system response) also activate immature B cells through secretary signalling messengers, called cytokines. Activated B cells then develop into short-lived plasma cells and long-lived memory cells (Figure 3).
Figure 3. Cellular activation of B cells
Short-lived plasma cells produce immunoglobulins (also known as antibodies) that are specific for the triggering antigen. This is called the primary immune response.
Memory cells are long-lived and reside in the blood, bone marrow and lymph nodes. When activated, memory cells respond quickly upon second exposure to the antigen – this is called the secondary immune response. Activated memory cells become centroblasts, which give rise to centrocytes.
Some centrocytes become plasmablasts which can develop into short-lived plasma cells in the lymph node, or travel back to the bone marrow. In the bone marrow they develop into long-lived plasma cells and it is these cells that produce the majority of immunoglobulins that fight infection in the body. These cells also give rise to myeloma if they become malignant.
It is important to note that although plasma cells exist in the lymph nodes and in the lining of the gut, myeloma develops only from plasma cells in the bone marrow. This is thought to be because myeloma arises, in part, due to the coincident interaction of myeloma cells with a number of factors found solely in the bone marrow micro-environment. It is possible, although rare, for myeloma cells, once developed, to travel from the bone marrow to the lymph nodes and/or the gut lining.
The following animation summaries the pathophysiology of the myeloma B cell: