In immunofixation electrophoresis, if a band reacts with anti IgA reagent and the heavy chain is present, which immunoglobulin heavy chain is indicated?

• A. IgA
• B. IgG
• C. IgM
• D. IgD

Answer: (A)

Immunofixation electrophoresis identifies the class of an immunoglobulin by applying antisera that are specific for each heavy-chain class after the proteins are fixed on the membrane. If a band reacts with anti-IgA reagent, that means the heavy chain present in that immunoglobulin is the IgA class (the alpha heavy chain). In other words, the immunoglobulin shown is IgA, not IgG, IgM, or IgD. The band would only react with the respective antisera if the heavy chain were of that class, so a reaction with anti-IgA confirms IgA.