Histology, B-Cell Lymphocyte

Excerpt

B cells or B lymphocytes (bursa-derived cells) are essential components of adaptive immune response, primarily responsible for humoral immunity in mammals. B-cell production in humans is a lifelong process that starts in the fetal liver, intrauterine, and bone marrow after birth. B-cell development originates from hematopoietic stem cells and involves several stages of early differentiation, progressing through maturation, antigen interaction, and antibody synthesis. Through this process, B cells acquire 2 essential features of adaptive immunity—the ability to distinguish between self and non-self (recognizing foreign antigens rather than self-antigens) and the ability to form a memory of previous antigen encounters. This memory allows for a more effective and rapid response upon subsequent interactions with the same antigens.

B cells acquire their name from early experiments on chickens that demonstrate the synthesis of antibodies. Max Cooper found that antibody production in chickens required an organ called the bursa of Fabricius in the 1960s. Surgical removal of the bursa inhibited antibody production. The cells responsible for antibody production were called bursa-derived or B cells. In contrast to chicken, B-cell development in humans occurs predominantly in the bone marrow. Many B-cell differentiation pathways demonstrate characteristic specific surface markers (CD markers) and immunoglobulin gene arrangements. In addition, developmental checkpoints exist along the pathways to determine whether a cell follows the normal or alternative pathways, resulting in cell death.

B cells are predominantly found in the cortex of lymph nodes and form part of the B-cell follicles, which can be classified into 2 types. Primary follicles are small and uniform, containing naive or resting B cells. In contrast, secondary follicles are characterized by the presence of a germinal center, where B cells undergo activation, proliferation, and differentiation into plasma cells or memory B cells. The germinal center consists of a light zone containing centrocytes and a dark zone containing centroblasts. In the spleen, B cells are located in the white pulp, specifically in periarteriolar lymphoid sheaths and follicles, similar to those observed in lymph nodes. In addition, B cells are prominent in mucosa-associated lymphoid tissue, including in the tonsils and Peyer's patches, where they also form germinal centers.