Functions Of Antibodies In The Immune System

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Functions Of Antibodies In The Immune System

An antibody, also called an immunoglobulin, is a protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies recognize and bind to antigens to remove them from the body. A wide range of substances are recognized by the body as antigens, including pathogens and toxins such as insect venoms.

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When a foreign substance enters the body, the immune system recognizes it as foreign because the molecules on the surface of the antigen are different from those found in the body. To eliminate an invader, the immune system requires several processes, including one of the most important – the production of antibodies. Antibodies are produced by special white blood cells called B lymphocytes (or B cells). When an antigen binds to the surface of a B-cell, it stimulates the B cell to divide and mature into a group of identical cells called a clone. Mature B cells, called plasma cells, produce millions of antibodies in the blood and lymphatic system.

As the immune system circulates, it attacks and neutralizes the antigens that cause the immune response. Antibodies attack by binding to antigens. For example, an antibody binding to a toxin can neutralize the toxin by changing its chemical structure; Such antibodies are called antitoxins. By binding to certain invading viruses, certain antibodies can stabilize such viruses or prevent them from entering the immune system. In some cases the antibody-coated antigen undergoes a chemical chain reaction with complement, a series of proteins found in the blood. Complement responses can result in lysis (explosion) of the invading microbe or attract microbial cells that ingest, or phagocytose, the invader. Once initiated, antibody production continues for several days until all antigen molecules are removed. Antibodies remain in circulation for several months, providing extended protection against that particular antigen.

B cells and the immune system together provide one of the most important functions of the immune system, which is to recognize an invading antigen and produce large amounts of protective proteins that scan the body to remove all traces of that antigen. . Combined B cells recognize an almost unlimited number of antigens; However, each B cell can only bind one type of antigen. B cells recognize antigens through proteins, called antigen receptors, located on their surfaces. The antigen receptor is actually an antibody protein that is not secreted but is bound to the membrane of B cells.

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All antigen receptors found on a particular B cell are the same, but receptors found on other B cells are different. Although their general structure is similar, the difference lies in the antigen-binding site-antigen-binding, or antibody-binding site. This structural variation between antigen-binding sites allows different B cells to recognize different antigens. The antigen receptor does not necessarily recognize the entire antigen; Instead it binds to only part of the antigen’s surface, an area called the antigenic determinant or epitope. Binding between receptor and epitope occurs only when their properties match. In this case, the epitope and receptor fit like two pieces of a puzzle, an event that is necessary to activate the production of B cells of the immune system. Combined with the heterogeneity offered by cellular expression systems present major challenges in biomanufacturing problems. Assessing the quality of biomanufacturing. Biologics such as monoclonal antibodies (MAbs). Information related to critical quality attributes (CQAs) of MAb drug candidates during early stage drug development is not known. Physical, structural and functional analysis should be established as soon as possible to accelerate development and reduce risk through a better understanding of product characteristics.

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High-resolution analytical techniques are required to answer questions regarding product variation with respect to charge, size, glycan structure, and other post-translational modifications. In addition to that analysis, characterization of biological agents helps scientists answer critical questions about how a drug works and provides insight into its structure-activity relationships.

Investing in complex specificity analysis early in development can help reduce risks throughout the product lifecycle by ensuring that the MAb candidate has the required basic properties and functionality, which can remove many unknowns during the development process. . The use of critical testing provides initial information about the product and helps inform important decisions at key stages such as clone selection, upstream and downstream process optimization, and determination of CQAs.

Therapeutic antibodies can work in several ways. Their clinical efficacy often depends on a combination of biological activities mediated by antigen-binding (Fab) and crystallinity (FC) fragments (Figure 1). Key performance information includes how strongly the immunosuppressive drug candidate binds to the target(s) and how well it engages the patient’s immune system to provide innate and/or complementary cytotoxic effects (effector activities).

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Fab regions bind with high specificity to their antigenic drug targets. This binding alone can often induce biological effects such as cell death or cell proliferation. When the antibody binds to the target, the Fc regions can bind to Fcγ receptors on immune cells or C1q related proteins, which can bring about additional effector functions. In all of these cases, the binding relationship is CQA that must be characterized, followed by complement-dependent cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and/or cell activity.

Correlating physical and/or structural data with biological activity helps researchers determine whether a product has the desired properties for clinical use. For example, information on potential effector effect is particularly important for tumor-targeted MAb therapy where ADCC and/or CDC may contribute significantly to overall efficacy. Even if functional activities are not considered to contribute to the mechanism of action (MoA), regulatory authorities need an understanding of all possible biological activities because functional activities may have an impact on drug safety. It is therefore important to identify all the different biological functions that antibodies mediate.

The degree of specificity of binding and functional activities in early development can vary greatly between drug developers. Such differences may depend on the potential contribution of effective activities to the MoA, the level of risk tolerance, and the availability of resources and technical capacity. However, to minimize risk, critical binding functions and functionality should be tested early in development.

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In contrast, for biosimilar MAbs, detailed comparison of all binding and functional activities using multiple orthogonal methods as early as possible in development to assess the level of molecular similarity to the original and satisfy comparative test expectations requires To enable clinical testing. Therefore, the approaches, timing, and methods used to demonstrate MAb biological activity vary. But the selective use of novel, sensitive methods provides important insights to support successful MAb development.

To achieve a level of product understanding that helps ensure quality and enables risk reduction, sensitive cell-based assays that demonstrate potential mechanisms of biological activity in vivo are essential. Such tests are used to determine the importance of structural features and variations in the biological activity of a drug or, in the case of biosimilars, to assess the functional significance of differences between molecules.

Fcγ receptor and C1q binding affinity and their effects on ADCC, CDC, and ADCP activities should be assessed separately using the most sensitive or cell-based binding assays available. Understanding all possible biological functions of an antibody allows selecting the most appropriate methods of positioning the actors to establish and monitor the product’s CQAs.

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Binding Kinetics: Surface Plasmon Resonance (SPR) has become the dominant technology for analyzing Fab-based and Fc-based antibody kinetic binding interactions. This kinetic analysis method is more informative than enzyme-linked immunosorbent assays (ELISAs) because it provides real-time convergence and dissociation rates. Other rapid methods for analyzing binding interactions such as SPR and biolayer interferometry (BLI) are important for initial characterization because they are fast and inexpensive, require small sample volumes and provide detailed information on the nature of binding interactions. .

Functional activity: Evaluating functional activity such as whether the antibody engages components of the immune system—eg, natural killer (NK) cells, complement, and macrophages—risks selecting an ineffective drug to provide functional activity. reduces Building on predictive information of potential effector functions obtained by Fcγ receptor or C1q binding analysis requires further elucidation of functional functions using physiologically relevant cell-based assays to reveal the full story about MAb biological activity. happens However, cell-based methods used to reveal effector functions can be challenging to perform and require the availability of human blood cells/complements.

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