Q. I just had a quick question as I was going through some immunology notes and wondering if you could clarify what they mean when a person develops an anti antibody? I get confused because when I hear two negatives, does that make it a positive body? Now that I wrote that, it sounds silly, but I’m still confused as to what they mean. Can you advise?
A. An anti-antibody is an antibody that binds to other antibodies! Weird. Usually antibodies bind to antigens (little amino acid sequences in a bigger molecule, for example). But they can bind to anything, really – including other antibodies. Sometimes this can cause problems. For example, patients with rheumatoid arthritis make something called rheumatoid factor, which is an antibody (happens to be IgM) that binds to the patient’s own IgG. This binding can cause the formation of immune complexes (just a bunch of antibodies bound together, floating around) which can lodge in the joint space and cause inflammation.
One good use for anti-antibodies is in the test called the direct antiglobulin test (or Coombs’ test). This test is used to see if a patient’s red cells are coated with antibody. You take the patient’s red cells and add a little Coombs’ reagent (an antibody that will bind to basically any human immunoglobulin. It’s made by injecting human Ig into another animal, like a mouse.). If the patient’s red cells are coated with antibody, the Coombs’ reagent will attach to those antibodies, linking red cells together into a big clump that you can see with your naked eye. Pretty ingenious test. Anti-antibodies are also used in a lot of other immunologic tests, like immunofluorescence, enzyme-linked immunosorbent assays (ELISA) and western blots.
So: anti-antibodies are cool when you use them in tests, not cool when they form on their own in your body.