Immunoglobulins are antibodies produced by plasma cells. Which statement is true?

• A. They are classified into five types: IgA, IgD, IgE, IgG, and IgM.
• B. They are hormones that regulate growth.
• C. They are enzymes that digest proteins.
• D. They are lipids involved in energy storage.

Answer: (A)

Immunoglobulins are antibodies produced by plasma cells, and they come in five main classes: IgA, IgD, IgE, IgG, and IgM. This classification is true because each class is defined by its heavy chain and distribution in the body, enabling different immune defense roles. The other statements aren’t accurate: immunoglobulins are not hormones that regulate growth, not enzymes that digest proteins, and not lipids involved in energy storage. As antibodies, they bind antigens to help neutralize pathogens, with each class contributing differently—IgM often being the first responder and good at activating complement, IgG providing most systemic protection, IgA protecting mucosal surfaces, IgE mediating allergic responses, and IgD mainly acting as a B cell receptor. This is why the statement about five classes is the correct one.