Which of the following statements is true? (A) An antibody has one antigen-binding site. (B) A lymphocyte has receptors for a single antigen. (C) Every antigen has a single epitope. (D) A liver or muscle cell makes two classes of MHC molecule

Verified step by step guidance

1. Identify the basic functions and structures of antibodies, lymphocytes, antigens, and MHC molecules.
2. Understand that antibodies typically have two antigen-binding sites, which allows them to bind to specific antigens.
3. Recognize that lymphocytes, such as B cells and T cells, have receptors that are specific to a particular antigen, but each lymphocyte is specific to only one type of antigen.
4. Acknowledge that antigens can have multiple epitopes, which are the parts of an antigen that are recognized by the immune system.
5. Review the roles of MHC (Major Histocompatibility Complex) molecules, noting that there are two classes (Class I and Class II), and most nucleated cells including liver and muscle cells express Class I MHC molecules, while Class II MHC molecules are typically expressed by antigen-presenting cells.

Key Concepts

Antibodies and Antigen-Binding Sites

Antibodies are proteins produced by B cells that specifically bind to antigens, which are foreign substances that trigger an immune response. Each antibody typically has two identical antigen-binding sites, allowing it to bind to two identical epitopes on an antigen, enhancing its ability to neutralize pathogens.

Lymphocyte Receptors

Lymphocytes, including B cells and T cells, have specific receptors that recognize and bind to particular antigens. Each lymphocyte is programmed to respond to a single antigen, which allows for a highly specific immune response. This specificity is crucial for the adaptive immune system's ability to remember and target pathogens effectively.

Epitopes and Antigens

An epitope is the specific part of an antigen that is recognized by the immune system, particularly by antibodies, B cells, or T cells. Antigens can have multiple epitopes, allowing them to elicit a diverse immune response. Therefore, the statement that every antigen has a single epitope is incorrect, as many antigens can present multiple distinct epitopes.