Antibodies are a vital part of the human immune system. It is also known as an immunoglobulin and is a large, Y-shaped protein with the abilities to identify and neutralize foreign objects by recognizing markers on pathogenic cells’ surfaces called antigens. There are five primary classes of immunoglobulins: IgG, IgM, IgA, IgD, and IgE. These classes are distinguished by the type of heavy chain found in the molecule. Antibodies serve multiple purposes: neutralization, agglutination, phagocytosis, precipitation, activation of complement system, and cell lysis — all processes that take place when antibodies are produced in exposure to a pathogen. Antibodies can be passive or active, and within these two categories, they can be natural or artificial. Antibodies are part of the adaptive immune system, which is related to memory.
When an organism encounters a pathogenic foreign agent for the first time, specialized cells (macrophages, dendritic cells) detain the molecules and begin the process of breaking them down, so that antigens can be presented to B-cell lymphocytes. Lymphocytes are white blood cells, where B-cells are those that matured in the bone marrow, and T-cells are those matured in the thymus. T-cells are used to activate the correct B-cell (specific to the antigen). Plasma in B-cells is used to create antibodies. In this process, memory cells can survive to initiate the secondary response for future exposure to the same specific antigen.
Of the B-cells, there are different types. Plasma B-cells account for the majority of B-cells — they are short-lived and produce large quantities of specific antibodies. Memory B-cells, on the other hand, hold a smaller proportion of the B-cells, but they are long-lived, therefore achieving long-term immunity for future encounters of the same antigen, and is one of the reasons why vaccines work. For the body’s acquired immunity, polyclonal activation takes place where several different T-cells and B-cells are stimulated in order to produce a variety of specific antibodies in the future and allows them to respond to different antigens that are presented.
Sometimes, dendritic cells and macrophages present antigenic fragments to T-cells. Dendritic cells attach antigens to proteins and occur in the ribosomes made in the endoplasmic reticulum and golgi apparatus; exocytosis takes place, and dendritic cells present antigens on the surface such that other cells identify it. Macrophages recognize markers to detect foreign agents. T-cells are often called helper T-cells, as they aid in the process of antigen presentation to B-cells. When helper T-cells are activated, they release cytokines, which stimulate specific B-cells that produce specific antibodies in response to the antigen, which allows it to divide and form clones, as part of the body’s acquired immunity (clonal selection). In other words, the T-cell presents information on the type of receptor desired to form the T-cell and goes through mitosis to multiply. The B-cell then binds and gets activated to make antibodies.
Once antigen presentation (to the B-cell) occurs, somatic hypermutation allows the B-cell to start the code of a new antibody that contains the specific antigen-binding site, as each antigen is unique. The antigen-binding site is in the variable region with the capability to bind specifically to an epitope from the antigen. Each one of the antibodies produced by the B-cell lymphocyte is unique against one epitope. The B-cell begins to release antibodies into the bloodstream when antibodies that are specific to the respective epitope can be encoded. These released antibodies will bind with the pathogen and allow the immune system to eliminate the foreign molecule from the body system.
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Written by: Erin Zhang
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References:
“How are Antibodies Produced?”. (n.d.). Pacific Immunology. Retrieved from https://www.pacif
Alberts B, Johnson A, Lewis J, et al. “B Cells and Antibodies.” Molecular Biology of the Cell.
4th edition. (2002). Garland Science. Retrieved from https://www.ncbi.nlm.nih.gov/
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