Antibody Structure and Function

The Adaptive Immune System
Lymphatic & Immune Systems
Systems Biology

Systems Biology

Antigens are molecules capable of being bound by an antibody or T-cell receptor, and certain regions of these antigens called epitopes serve as binding sites. Haptens are small, incomplete antigens that require attachment to a larger carrier molecule to stimulate an immune response.

Antibodies, also known as immunoglobulins, are glycoproteins secreted by B-cells and plasma cells. They are typically composed of two heavy chains and two light chains held together by disulfide bonds. Both chains contribute to the antibody's variable region, which includes antigen-binding sites or paratopes, and the constant region, which is identical between antibodies of the same class. Antibodies are classified into five isotypes: IgD, IgA, IgM, IgG, and IgE, each varying in location and function.

Lesson Outline

<ul> <li>Introduction: Antibodies (molecules that bind antigens, epitopes, and haptens)</li> <ul> <li>Antigens: found in and on cells and pathogens, can be bound by antibodies and T-cell receptors</li> <li>Epitopes: regions of antigens that serve as binding sites</li> <li>Haptens: small incomplete antigens, need a carrier molecule to stimulate an immune response</li> </ul> <li>Antibody structure: immunoglobulins (glycoproteins secreted by B-cells and plasma cells)</li> <ul> <li>Consist of two heavy chains and two light chains, connected by disulfide bonds</li> <li>Antigen-binding region (paratope): includes parts of both heavy and light chains</li> <li>Variable region: differs in antibodies produced by different B-cells</li> <li>Constant region: identical in all antibodies of the same isotype or class</li> </ul> <li>Five antibody classes: IgD, IgA, IgM, IgG, and IgE</li> <ul> <li>IgM: first antibody produced in response to a new infection, activates complement system</li> <li>IgA: found in secretions and mucosal tissues, blocks infection process</li> <li>IgG: most prevalent isotype, 80% of antibodies in adults, involved in activation of innate immune responses</li> <li>IgE: stimulates mast cells and basophils to release histamines during allergic reactions</li> <li>IgD: function not fully understood; found on the surface of B-lymphocytes as the B-cell receptor and is involved in B cell activation</li> </ul>

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What is the basic structure of an antibody and how does it relate to its function?

Antibodies, also known as immunoglobulins, are Y-shaped proteins that play a crucial role in the adaptive immune system. They consist of two types of polypeptide chains - heavy (H) chains and light (L) chains, which form two different regions of the antibody - the variable and constant regions. The variable region varies between different antibodies, allowing them to recognize and bind to a wide range of antigens. On the other hand, the constant region is identical within antibodies of the same isotype or class, providing functional properties such as effector functions and determining antibody class. Each antibody has two antigen-binding sites located at the ends of the Y-shape, formed by the interaction of variable regions from both the heavy and light chains. This unique structure allows antibodies to bind specifically to their corresponding antigens, neutralizing or marking them for destruction by other immune cells.

What is the role of antigens and epitopes in antibody recognizing and binding?

Antigens are molecules, typically proteins or polysaccharides, found on the surface of pathogens or other foreign substances that can initiate an immune response. Epitopes, also known as antigenic determinants, are the specific areas on the antigen that are recognized and bound by antibodies. Each antibody has a unique paratope (the antigen-binding site) that matches the epitope on its specific antigen, allowing for high specificity in the antibody-antigen interaction. This specific binding helps in the neutralization or marking of the antigen for elimination by the immune system.

What are the different classes of immunoglobulins and their functions?

There are five major classes of immunoglobulins, each with different roles in the immune system:IgA - Found mainly in secretions such as saliva, tears, and breast milk; it provides mucosal immunity, protecting body surfaces from pathogens.IgD - Involved mainly in B-cell activation and maturation.IgE - Binds to allergens and triggers histamine release from mast cells and basophils, playing a role in allergic reactions and protection against parasites.IgG - The most abundant immunoglobulin in the blood, it participates in various immune functions, including neutralization, opsonization, and complement activation. It can cross the placenta, providing passive immunity to the fetus.IgM - Produced earlier in an immune response, it is usually the first antibody to be made against a new antigen and functions in neutralizing pathogens and activating the complement system.

What are haptens and how do they elicit an immune response?

Haptens are small molecules that, on their own, are unable to elicit an immune response. However, when they bind to larger carrier proteins, they become antigenic and can stimulate antibody production. The immune system then recognizes the hapten-carrier complex as a foreign substance and generates specific antibodies against it. This process is the basis for many allergy and autoimmune responses, as the hapten can sometimes lead to a misidentification of the body's own proteins as foreign substances, triggering an immune response against self-antigens.