2C.5 Antibodies in medicine

• what are monoclonal antibodies?

  identical copies of an antibody.
• why do we use monoclonal antibodies?


  they are specific to one binding site (antigen) so can target specific chemicals or cells.
• name three uses of monoclonal antibodies.


  • pregnancy tests. • anti cancer drugs. • elisa tests.
• describe what happens during a pregnancy test.

  • HCG hormone in urine binds to the mobile HCG antibody in the reaction zone. (antibody-antigen complex) • it passes up the stick and binds to the immobilised HCG antibodies in the results zone. • left over HCG mobile antibodies (unbinded) will travel up to the control zone. • blue dye will appear in both the control and result zone to show a positive test.
• describe how we use antibodies for anti cancer drugs.

  • cancer cells have tumour marker antigens that aren't found on normal body cells. • monoclonal antibodies can be made to specifically bind to these antigens. • anti cancer drugs can be attached to the antibodies.• this means when they bind the anti cancer drugs will accumulate near the cancer cells and ignore healthy cells.• less side affects.
• what are elisa tests used for?

  to see weather patients have certain antigens/antibodies.
• describe a direct elisa test.

  • antigens from a patient are bound to the inside of a well plate. • a complimentary detection antibody (with an attached enzyme) is added. • if the antigen of interest is present the antibody will bind and become immobilised. • a substrate solution is added that will react with the attached enzyme and cause a colour change if the antigen is present.
• describe an indirect elisa test for HIV antibodies.

  • HIV antigen is bound to a well plate. • patients blood sample is added to the well.• HIV specific antibodies will bind to the antigen.• the well is washed to remove unbound antibodies.• a secondary antibody (with an enzyme attached) is added and binds to the primary HIV antibody. • the well is washed again. • solution containing substrate is added with reacts with the enzyme to produce a colour change.
• what are the strengths of direct elisa tests?

  it is a faster procedure as there are less steps.
• what are the weaknesses of direct elisa tests?

  the immobilising agent is not specific so anything from the sample could stick e.g. other proteins.
• what are the strengths of indirect elisa tests?

  higher sensitivity as more than one secondary antibody can bind to the primary antibody meaning the result is more amplified/stronger colour.
• what is the weakness of indirect elisa tests?


  its is a longer procedure as more steps are needed.
• what are the ethical issues with elisa tests?

  animals are tested on.