Final answer:
The common feature among all the 5 isotypes of antibody is that they are all glycoproteins and have a Y-shaped structure with two identical heavy chains and two identical light chains. Each class of antibody has a specific function in the immune response.
Step-by-step explanation:
The common feature among all the 5 isotypes of antibody is that they are all glycoproteins and have a Y-shaped structure with two identical heavy chains and two identical light chains. In each antibody class, the heavy chain determines the class or isotype. The five classes of antibodies are IgM, IgG, IgA, IgD, and IgE. Each class has a specific function in the immune response.