Can an antibody penetrate the host cell to bind intracellular antigen?

Antibodies are proteins that are part of the immune system that help identify and destroy foreign substances in the body. Antibodies can be produced in response to a foreign molecule or antigen. When an antibody binds to an antigen, it marks the antigen for destruction by the immune system.

Usually, antibodies do not penetrate the host cell to bind intracellular antigens. This is because antibodies are too large to pass through the cell membrane, which is a selectively permeable barrier. Antibodies can only bind antigens on the cell surface of the host cell or in the extracellular space. However, there are some exceptions to this rule.

For instance, some antibodies, like the anti-HIV antibody, can enter the host cell by binding to a specific receptor on the cell surface and then being transported into the cell. Once inside the cell, the antibody can bind to intracellular antigens and help destroy infected cells. Besides, in certain cases, antibodies can be internalized by cells via mechanisms like endocytosis or phagocytosis, allowing them to access intracellular antigens.

Additionally, some antibodies can also bind to antigens that are released from the host cell, such as those released by exocytosis or cell death. In this case, the antibody can bind to the antigen in the extracellular space and help destroy the infected cell.