Bsejt

Bsejt, or B cell, is a lymphocyte central to the adaptive immune system. B cells surveil the body for foreign antigens and primarily defend through antibody production. They originate from hematopoietic stem cells in the bone marrow, where they rearrange immunoglobulin genes to form a unique B cell receptor (BCR). During maturation they pass through pro-B, pre-B, and immature stages to become mature naive B cells expressing surface immunoglobulin and requiring signaling cues from bone marrow and peripheral tissues to complete development.

When the BCR engages its antigen, Bsejt internalizes and presents fragments on MHC class II, enabling helper T cell interaction. With T cell help, they can proliferate, undergo class switch recombination and somatic hypermutation to increase antibody affinity. Some differentiate into plasma cells that secrete antibodies; others become memory B cells for rapid response on re-exposure. Bsejt also act as antigen-presenting cells and secrete cytokines that influence other immune cells.

Bsejt subsets include conventional B2 cells, B1 cells producing natural antibodies, and marginal zone B cells in the spleen that respond to blood-borne antigens. Regulatory B cells with anti-inflammatory activity have been described. Antibodies produced by Bsejt include IgM, IgG, IgA, IgE, and IgD; isotype switching is guided by signals from helper cells and cytokines.

Clinical relevance: B sejt defects cause hypogammaglobulinemia and susceptibility to infection. Bsejt–related cancers, such as lymphomas and leukemias, are common hematologic diseases. Therapies targeting Bsejt, including anti-CD20 antibodies and chimeric antigen receptor (CAR) T cell approaches, are widely used in treatment protocols.