B cells and antibodies play an important role in the immune system. Antibodies have a Y-shaped structure with two heavy chains and two light chains that give them different functions. There are five major classes of antibodies (IgG, IgA, IgM, IgE, IgD) that carry out effector mechanisms like complement activation, neutralization, and opsonization. B cells produce polyclonal antibodies that recognize multiple antigens, while monoclonal antibodies produced via hybridoma technology each recognize a single antigen. Monoclonal antibodies have various clinical applications in diagnosis and treatment.