Q. What do they mean when they say 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!

I know. It’s 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.

However, these anti-antibodies can be very useful if they are used on purpose in laboratory tests. One such test is 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 an anti-antibody (also called anti-human globulin, or Coombs’ reagent, after the person who devised the test). The anti-antibody is made by injecting human antibodies 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-based tests, enzyme-linked immunosorbent assays (ELISA) and western blots.

Bottom Line

Anti-antibodies are cool when you use them in tests, not cool when they form on their own in your body.