24.1Introduction B cetl Secretion of antibodies by B cell requires helper T cells Figure 24.1 humoral 人人A immunity is conferred by the Antibodies Antigen binding of free antibodies to antigens to form antigen Antibody-antigen antibody complexes that are complex removed from the bloodstream by macrophages or that are attacked directly by the complement proteins Macrophage 消当 ComplementFigure 24.1 Humoral immunity is conferred by the binding of free antibodies to antigens to form antigen￾antibody complexes that are removed from the bloodstream by macrophages or that are attacked directly by the complement proteins. 24.1 Introduction