Passive immunity involves injecting the antibodies against a pathogen into a patient. It’s used in cases in which someone has already become infected or is likely to become infected with a particular microbe. They can be created by genetic engineering or taken from the blood serum of an infected human, which is called an antiserum. It’s used for diseases like tetanus, rabies, and hepatitis B.

Monoclonal antibodies

Monoclonal antibodies are antibodies which are cloned using one B-lymphocyte. It’s too difficult to make them in test tubes (in vitro) however, so they need to make them in living cells or in vivo. One way is to use mice.

• A mouse is injected with the antigen protein for which the antibodies are wanted. The mouse produces B-lymphocytes in its primary immune response.
• A few days later the B-lymphocytes are removed from the mouse’s blood. The blood contains a multitude of B-lymphocytes for different antigens so the right ones need to be isolated.
• To achieve this, the blood is diluted and injected into hundreds of wells within an immunoassay plate with one cell per well.
• The cells multiply and secrete their antibodies.
• The wells can then be tested to find the right antibodies and the B-cells grown to make millions of cloned cells, each producing the same antibodies known as monoclonal antibodies.

Monoclonal antibodies will only bind to one specific protein. By chemically attaching a coloured molecule onto the antibody it’s then possible to track specific proteins in a sample.

Monoclonal antibodies have a number of uses, including:

• They can target drugs to a specific type of cell in the body. Known as the ‘magic bullet’, the drug is attached to the constant region of the antibody and when this antibody/drug complex is injected into a patient it only reaches the target cells.
• They can target cancer cells with radioactive substances which limits the damage to healthy cells.
• If a florescent chemical is attached to them they can show up specific organelles in a cell.