25.27 : 抗体の作用

Antibodies recognize and bind antigens to form antigen-antibody complexes for pathogen elimination.

After binding to an antigen, the antibody neutralizes the pathogen by obstructing the antigen's interaction with receptors on the host cell membrane, curbing the spread of infection.

As each antibody molecule has two binding sites for the same antigen, it can cross-link antigens on different pathogenic molecules.

As a result, antibodies can link different antigenic molecules into large, insoluble immune complexes.

When soluble antigens, such as toxins, form large complexes, they precipitate out of the solution.

In contrast, antigens on bacterial cells or viral particles that are cross-linked by antibodies cause clumping or agglutination.

In both cases, the phagocytes easily capture and engulf these large immune complexes.

When multiple antibodies bind closely on a cell, their stem regions align to allow the binding of complement proteins, triggering pathogen lysis.

Additionally, the coat of antibodies and complement proteins opsonizes, or tags, pathogens for phagocyte recognition.

These opsonized pathogens are easily gripped by phagocytes for effective elimination.