Bovine B cells are a major population of adaptive immune lymphocytes responsible for antibody production and humoral immunity in cattle (Bos taurus). These cells develop from hematopoietic stem cells in the bone marrow, where they undergo immunoglobulin gene rearrangement to generate diverse B cell receptors (BCRs) capable of recognizing a wide range of antigens. Mature bovine B cells express characteristic surface markers such as surface immunoglobulin (IgM or IgG), CD19, CD21, CD40, and MHC class II molecules, which allow them to recognize antigens and interact with other immune cells. Upon antigen recognition and appropriate stimulation-often with help from CD4⁺ T helper cells-bovine B cells become activated and differentiate into antibody-secreting plasma cells or long-lived memory B cells. Plasma cells produce immunoglobulins including IgM, IgG1, IgG2, IgA, and IgE, which play critical roles in neutralizing pathogens, opsonization, and complement activation. In cattle, B cells contribute to immune defense against bacterial, viral, and parasitic infections, including pathogens such as bovine viral diarrhea virus (BVDV), bovine leukemia virus (BLV), Mycobacterium bovis, and various respiratory and enteric pathogens. Bovine B cell responses are also important for vaccine-induced immunity and protection against infectious diseases affecting livestock. Because humoral immunity is a key component of disease resistance and vaccine efficacy in cattle, bovine B cells are widely studied in veterinary immunology, vaccine development, and host-pathogen interaction research.