Multiple choice Which immunoglobulin class is only found in mammals? IgA IgG IgM IgD IgE Reveal answer Fill a bubble to check yourself E Correct answer Explanation Immunoglobulin E is a class of antibody (or immunoglobulin (Ig) isotype) that has been found only in mammals. IgE is the least abundant isotype of all antibodies but it is capable of triggering the most powerful immune reactions.