What are B cells (B lymphocytes)? Functions and antibody production

The human body constantly encounters various pathogens. To protect itself against these pathogens, our body has developed the immune system . This system consists of various components. It is broadly divided into the innate immune system and the adaptive immune system . Of these defense systems, the most effective is adaptive immunity, which consists of various cells. One type of these cells is the B cell (B lymphocyte), which produces antibodies to provide the body's humoral (fluid-based) defense. Humoral defense protects the body against free bacteria, molecules produced by viruses and various other antigens. This protection is provided by antibodies produced by plasma cells, a differentiated form of B cells. Antibodies bind to antigens and suppress their harmful effects (cancer cells also produce their own specific antigens).

The diagram below shows B-cell activation following a viral infection.

B cells are naturally present in the body, and different B cells carry different antibodies. To conserve energy and resources, they do not multiply unless necessary. Depending on its effects, a pathogen entering the body for the first time is likely to evade innate immunity. The antigen that passes this system binds to a B cell already present in the body whose antibody is complementary to it, causing that cell to multiply. This pathogen-specific multiplication is called clonal expansion. Once B cells have multiplied sufficiently, they divide into plasma cells and the memory B cells as two subgroups.

Plasma cells produce and release antibodies into circulation to fight free antigens. Memory cells do not participate in the active fight against the antigen; instead, they wait in readiness for a possible later encounter with the same antigen. This enables a faster and more effective response when the antigen enters the body again. Memory B cells also have a considerably longer lifespan than plasma cells.

- Related topic: A new micro-organ that houses memory B cells in our immune system has been discovered

The importance of B cells in cancer

Any problem that prevents B lymphocytes from working properly begins to cause difficulties in the immune system. For example, B-ALL (precursor B-cell acute lymphoblastic leukemia) is a cancer originating from B lymphocytes. In this cancer, mutated B lymphocytes can be recognized through their CD19 antigens. Recently, another important component of adaptive immunity, T lymphocytes has been used to prepare CAR-T cell therapy in which T lymphocytes with receptors specifically modified for the CD19 antigen are given to the patient to fight damaged B lymphocytes. This approach has led to substantial progress in ALL treatment.

The diagram below shows blood cells and the main immune-system cells: