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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.
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]
Each antibody binds to a specific antigen in a highly specific interaction analogous to a lock and key.. An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that cause disease.
Humoral immunity is the aspect of immunity that is mediated by macromolecules – including secreted antibodies, complement proteins, and certain antimicrobial peptides – located in extracellular fluids. Humoral immunity is named so because it involves substances found in the humors, or body fluids. It contrasts with cell-mediated immunity.
Vaccines are used to prevent infections by stimulating the body's own immunity, which includes the production of antibodies that destroy infectious agents such as bacteria and viruses. Some infections can be prevented or treated by antibodies derived from others sources such as blood donations or monoclonal antibodies made in laboratories.
We may speak of this as an “opsonic” effect (opsono - I cater for; I prepare victuals for), and we may employ the term “opsonins” to designate the elements in the blood fluids which produce this effect.” [3] Subsequent research found two main types of opsonin in blood that opsonised bacteria: complement proteins [4] and antibodies. [5]
Hence the term "polyclonal", which derives from the words poly, meaning many, and clones from Greek klōn, meaning sprout or twig; [3] [4] [5] a clone is a group of cells arising from a common "mother" cell. The antibodies thus produced in a polyclonal response are known as polyclonal antibodies.
Commensal bacteria in the GI tract survive despite the abundance of local immune cells. [6] Homeostasis in the intestine requires stimulation of toll-like receptors by commensal microbes. [6] When mice are raised in germ-free conditions, they lack circulating antibodies, and cannot produce mucus, antimicrobial proteins, or mucosal T-cells. [6]