Regulatory B Cells: Beyond Antibody Production in Immunity and Cancer

B lymphocytes, which originally develop in the bone marrow, are key components of humoral immunity and are responsible for antibody production. B lymphocytes arise from progenitor B cells (pro-B cells), which are located in the fetal liver during early development and are generated predominantly in the bone marrow before birth. Based on their stage of maturation and function, B cells are divided into many subsets. B cells play a critical role in the humoral immune response through antibody secretion; however, accumulating evidence indicates that B cells also have more diverse functions in the immune system. Different B cell subsets can modulate effector T-cell responses through antigen presentation, costimulation, and cytokine production. A distinct subpopulation of B cells, termed regulatory B cells (Bregs), negatively regulates cellular immune responses and contributes to the control of inflammation, infectious diseases, autoimmunity, and cancer. These cells may represent viable targets for therapeutic manipulation or immunomodulation independent of antibody production. In this review, we discuss the various B cell subsets and describe non-humoral functions of B cells, with particular emphasis on regulatory B cells and their roles in immunological diseases and cancer.