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Antibodies contribute to immunity in three ways: They prevent pathogens from entering or damaging cells by binding to them; they stimulate removal of pathogens by macrophages and other cells by coating the pathogen; and they trigger destruction of pathogens by stimulating other immune responses such as the complement pathway. [56]
The antigens and antibodies combine by a process called agglutination. It is the fundamental reaction in the body by which the body is protected from complex foreign molecules, such as pathogens and their chemical toxins. In the blood, the antigens are specifically and with high affinity bound by antibodies to form an antigen-antibody complex.
Polyclonal antibodies are collection of antibodies that target the same pathogen but bind to different epitopes. Polyclonal antibodies are obtained from human donors or animals that have been exposed to the antigen. The antigen injected into the animal donors can be designed in such a way to preferably produce neutralizing antibodies. [25]
Step 1: A macrophage engulfs the pathogen. Step 2: The macrophage then digests the bacterium and presents the pathogen's antigens. Step 3: A T helper cell binds to the macrophage and becomes an activated T helper cell. Step 4: The activated T helper cell binds to a B cell in order to activate the B cell.
Scheme of the complement system. The complement system, also known as complement cascade, is a part of the humoral, innate immune system and enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. [1]
Upon activation, B cells produce antibodies, each of which recognize a unique antigen, and neutralizing specific pathogens. [3] Antigen and antibody binding would cause five different protective mechanisms: Agglutination: Reduces number of infectious units to be dealt with; Activation of complement: Cause inflammation and cell lysis
"tag" pathogens for destruction by other cells by opsonizing, or coating, the surface of the pathogen; form holes in the plasma membrane of the pathogen, resulting in cytolysis of the pathogen cell, causing its death; rid the body of neutralised antigen-antibody complexes. The three different complement systems are classical, alternative and ...
Antibodies can also trigger the classical pathway – one of the three pathways of the complement cascade. Briefly, the C1 protein attaches to the pathogen surface and the antibody-antigen complex that culminates in the generation of C3 convertase, followed by the cleavage of C3 protein into C3a and C3b protein.