Antibodies are proteins that exist in bodily fluids, and are used both as a detection and response device by the immune system. Antibodies are made in plasma cells, which are a type of white blood cell, and are an integral part to the body’s natural defense system. In mammals, there are five primary types of antibodies, each with similar basic structures. The tips of the antibody protein can be incredibly different, however, and it is this part that interacts with the contaminant itself, allowing for millions of unique antibodies to exist.

Generally, antibodies serve as a kind of quick tagging device, which then alert other defensive cells to attack whatever they have tagged. They do this by binding with the invasive bit, known as the antigen. Each antigen has a part of it that is a very specific shape, known as the epitope. Each antibody is able to fit only one epitope, because of its specifically-shaped tip, making a sort of lock and key connection. Once this connection, known as an induced fit, has occurred, the antigen becomes immediately recognizable to defensive cells as an enemy.

After being tagged by antibodies, antigens generally come under attack by other cells. These include cells like the killer T cells, which can go after infected cells, such as those which have been compromised by a virus. This combination effort by antibodies and killer T cells allows the body to quickly respond to a wide range of antigens, helping to keep the body safe and free of infection.

Another type of responder cell, known as a B cell, actually has antibodies on it that assist it in its daily work. The B cell, because of its antibody component, is able to immediately detect an antigen by binding to it. It then absorbs both the antigen and the antibody, and processed them into peptides, which attract a helper T cell, which trigger a reaction in the B cell. This reaction causes the B cell to split and divide, creating millions of copies of an antigen specifically targeting the antibody it absorbed, creating an army of focused defensive cells.

Antibodies are also able to interact directly with pathogens in order to stop the spread of some viruses and illnesses, rather than simply tagging them. They do this by binding not just to any point on the antigen, but to the point where it connects to other cells to infect them. In this way, the antibody effectively neutralizes the threat that a virus will spread throughout a system, allowing it to be much more easily taken care of.

There are five main classes of antibodies found in mammals: IgA, IgD, IgE, IgG, and IgM. There are two types of IgA antibodies, and they are found primarily in areas with mucous membranes, like the respiratory tract and gut, as well as in breast milk, saliva, and tears. IgD is generally just found as the receptor on B cells before they’ve targeted a specific antigen, while IgM is found on B cells and targets pathogens. IgE is a class of antibodies that attacks allergens, and provokes a histamine response. IgG has four main types, and is responsible for most of the immune response against invasive pathogens.