3.4 Antigen-antibody interactions
2 min read•july 25, 2024
Antigen-antibody interactions form the foundation of immune responses. These interactions rely on various non-covalent bonds, each contributing to the strength and specificity of the binding. Understanding these bonds is crucial for grasping how antibodies recognize and neutralize threats.
Immunoassays harness antigen-antibody interactions for practical applications. Techniques like and Western blot enable disease diagnosis, vaccine development, and therapeutic interventions. These tools have revolutionized medical diagnostics and treatment strategies across various fields.
Antigen-Antibody Interaction Fundamentals
Types of antigen-antibody bonds
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- Non-covalent bonds form basis of antigen-antibody interactions
- Hydrogen bonds between hydrogen and electronegative atoms contribute significantly in large numbers
- Van der Waals forces weakly interact between adjacent molecules become significant in close proximity
- Electrostatic interactions attract oppositely charged ions or regions of molecules stronger than hydrogen bonds
- Hydrophobic interactions occur between non-polar regions maintain structure of antibody-antigen complexes
- Relative bond strengths from strongest to weakest
- Electrostatic interactions
- Hydrogen bonds
- Hydrophobic interactions
- Van der Waals forces
Antibody specificity and cross-reactivity
- Antibody specificity binds particular epitope determined by complementarity determining regions (CDRs)
- Cross-reactivity occurs when antibody binds multiple antigens with similar epitopes
- Factors affecting specificity and cross-reactivity
- Structural similarity between antigens (hemoglobin variants)
- Flexibility of antibody binding site adapts to different epitopes
- Environmental conditions alter binding (pH, temperature, ionic strength)
Immunoassays and Applications
Principles of immunoassays
- Enzyme-Linked Immunosorbent Assay (ELISA) detects antigens or antibodies using enzyme-linked antibodies
- Types: Direct, indirect, sandwich, and competitive ELISA
- Applications: HIV testing, food allergen detection, hormone level measurement
- Western blot separates proteins by gel electrophoresis detects with specific antibodies
- Sample preparation
- Gel electrophoresis
- Transfer to membrane
- Blocking
- Antibody incubation
- Detection
- Applications: HIV confirmation, Lyme disease diagnosis, protein research
- Common immunoassay features
- Labeled antibodies or antigens (fluorescent, radioactive)
- Specific antigen-antibody interactions ensure accuracy
- Signal amplification increases sensitivity (enzyme-substrate reactions)
Applications in vaccines and immunotherapies
- Vaccine development identifies protective antigens elicits specific antibody responses
- Monoclonal antibody therapies target specific antigens in cancer (Herceptin), autoimmune diseases (Humira)
- Passive immunization administers pre-formed antibodies for immediate protection (rabies immune globulin)
- Antibody engineering creates chimeric, humanized antibodies improves efficacy reduces immunogenicity
- Diagnostic applications use antigen-antibody interactions in rapid tests (pregnancy tests, COVID-19 antigen tests)
Key Terms to Review (17)
Adaptive immune response: The adaptive immune response is a specific and long-lasting defense mechanism that the body develops against pathogens, involving lymphocytes such as T cells and B cells. This response tailors itself to recognize and remember specific antigens, providing enhanced protection during subsequent encounters with the same pathogen. It works alongside the innate immune response to create a comprehensive defense strategy against infections.
Affinity: Affinity refers to the strength of the interaction between an antibody and its corresponding antigen. It is a crucial factor in determining how effectively antibodies can recognize and bind to antigens, influencing the overall immune response. The higher the affinity, the more tightly the antibody binds to the antigen, which is essential for neutralizing pathogens and facilitating their clearance from the body.
Avidity: Avidity refers to the overall strength of the binding between an antibody and its antigen, taking into account the combined effects of multiple binding sites. This concept emphasizes the importance of both affinity (the strength of a single binding interaction) and the multivalency of antibodies, which can bind to several antigens simultaneously. Avidity plays a crucial role in immune responses, as higher avidity often leads to more effective neutralization and clearance of pathogens.
Carbohydrate Antigen: Carbohydrate antigens are specific carbohydrate molecules that can provoke an immune response when recognized by antibodies. These antigens are often found on the surface of pathogens, cells, or in body fluids and can vary greatly in structure, leading to the formation of specific antibodies that bind to them. Understanding carbohydrate antigens is crucial for comprehending how the immune system identifies and responds to foreign substances.
Complement Fixation: Complement fixation is a specific immunological process where antibodies bind to antigens and activate the complement system, leading to the lysis of pathogen cells. This interaction enhances the immune response by facilitating opsonization and promoting inflammation, crucial in defending against infections.
ELISA: ELISA, or Enzyme-Linked Immunosorbent Assay, is a widely used laboratory technique that detects and quantifies proteins, antibodies, and hormones. This method relies on antigen-antibody interactions to provide precise measurements, making it crucial in areas like diagnostics, vaccine development, and research on immune responses.
Fab region: The fab region, or fragment antigen-binding region, is a part of an antibody that is responsible for binding to specific antigens. This region is crucial for the specificity of antibodies, allowing them to recognize and attach to unique structures on pathogens or foreign molecules, facilitating immune responses such as neutralization and opsonization.
Fc region: The fc region, or fragment crystallizable region, is the part of an antibody that interacts with cell surface receptors and complement proteins. It plays a crucial role in mediating the effector functions of antibodies, such as opsonization and activation of the complement system, thereby linking the adaptive immune response to innate immune mechanisms.
Humoral Immunity: Humoral immunity is a vital component of the immune system that involves the production of antibodies by B cells to identify and neutralize pathogens like bacteria and viruses. This type of immunity is crucial for recognizing foreign antigens and facilitating their elimination through various mechanisms, connecting deeply with other immune functions such as T cell activation and the development of vaccines.
IgG: IgG, or Immunoglobulin G, is the most abundant type of antibody in the bloodstream, playing a critical role in the immune response. It is known for its ability to neutralize toxins and pathogens, opsonize bacteria for easier phagocytosis, and activate complement pathways. IgG is a key player in forming a diverse range of antibodies and is involved in various immune interactions, highlighting its significance in immunity and disease processes.
IgM: IgM, or Immunoglobulin M, is the largest antibody isotype in terms of size and is the first antibody produced during an immune response. It plays a critical role in the early stages of immunity, particularly in responding to pathogens before the body has fully developed a specific immune response, making it key in both antibody diversity and class switching.
Neutralization: Neutralization refers to the process by which antibodies bind to antigens, blocking their harmful effects, and preventing them from interacting with host cells. This action is critical in immune defense, as it directly relates to how the immune system recognizes foreign invaders, the generation of diverse antibodies, the specific structures and functions of antibodies, and the intricate interactions between antigens and antibodies.
Neutralizing Antibodies: Neutralizing antibodies are a specific type of antibody that can block the biological effects of pathogens, such as viruses or toxins, by binding to them and preventing their interaction with host cells. This ability to neutralize threats is crucial for the immune response and is a key factor in the effectiveness of certain vaccines, which aim to elicit the production of these antibodies to provide protection against infections.
Opsonization: Opsonization is the process by which pathogens are marked for destruction by immune cells, making them more recognizable to phagocytes. This enhances the efficiency of the immune response by promoting the binding of these pathogens to immune cells, facilitating their ingestion and elimination. Opsonization connects to various immune mechanisms, including innate immunity, antibody function, antigen-antibody interactions, and complement activation pathways.
Precipitation: Precipitation refers to the formation of a solid antigen-antibody complex when soluble antigens react with their specific antibodies in a solution. This interaction is critical in immunology as it helps to visualize and measure the presence of antigens or antibodies, contributing to our understanding of immune responses and diagnostics.
Protein Antigen: A protein antigen is a type of molecule that is recognized by the immune system as foreign, triggering an immune response. These antigens are typically proteins found on the surface of pathogens like bacteria and viruses, or even on abnormal cells such as cancer cells. The interaction between protein antigens and antibodies is crucial in the immune response, helping to identify and neutralize potential threats to the body.
Western Blotting: Western blotting is a laboratory technique used to detect specific proteins in a sample through gel electrophoresis followed by transfer to a membrane and probing with antibodies. This method relies on the unique structure of antibodies to bind to their specific target proteins, allowing for the analysis of protein expression and size, which connects directly to understanding antibody function and antigen-antibody interactions.