An introduction to immunology and immunopathology

Antibody-mediated vs. cell-mediated immunity

Antibody-mediated immunity is the branch of the 

acquired immune system that is mediated by B-cell-

antibody production. The antibody-production pathway 

begins when the B cell’s antigen-binding receptor 

recognizes and binds to antigen in its native form. Local 

Th cells secrete cytokines that help the B cell multiply 

and direct the type of antibody that will be subsequently 

produced. Some cytokines, such as IL-6, help B-cells to 

mature into antibody-secreting plasma cells. The secreted 

antibodies bind to antigens on the surface of pathogens, 

flagging them for destruction through complement 

activation, opsonin promotion of phagocytosis and 

pathogen elimination by immune effector cells. Upon 

elimination of the pathogen, the antigen–antibody 

complexes are cleared by the complement cascade (see 

Fig. 

2

) [

2

].

Five major types of antibodies are produced by B cells: 

IgA, IgD, IgE, IgG and IgM. IgG antibodies can be further 

subdivided into structurally distinct subclasses with 

differing abilities to fix complement, act as opsonins, 

etc. The major classes of antibodies have substantially 

different biological functions and recognize and 

neutralize specific pathogens. Table 

2

 summarizes the 

various functions of the five Ig antibodies [

5

].

Antibodies play an important role in containing 

virus proliferation during the acute phase of infection. 

However, they are not generally capable of eliminating 

a virus once infection has occurred. Once an infection 

is established, cell-mediated immune mechanisms 

are most important in host defense against most 

intracellular pathogens.

Cell-mediated immunity does not involve antibodies, 

but rather protects an organism through [

2

]:

  

• The activation of antigen-specific cytotoxic T cells 

that induce apoptosis of cells displaying foreign 

antigens or derived peptides on their surface, 

such as virus-infected cells, cells with intracellular