Antibodies are immune system molecules that circulate throughout the body. These molecules are each custom-made to bind to specific antigens, which are foreign substances. Antibodies have specifically shaped binding sites to fit the antigen’s shape and chemical make-up. Antibody affinity refers to the strength of the bond between an antigen and a binding site on an antibody. In general, the higher the affinity, the better the antibody’s ability to recognize the invader.
Organic molecules make up every biological organism or part of an organism. The amount and arrangement of these molecules are unique to each organism. A bacterial cell, for example, has a structural cell membrane that contains a variety of molecules that each perform a specific function. Some may bind to external molecules to bring them into the cell, while others may aid in the attachment of the bacterium to a host cell during an invasion.
The human body has developed a system of cells and molecules that patrol the body and keep an eye out for intruders. Antibodies aren’t cells; they’re molecules that float around looking for invaders or bits of invaders to attack. The antibody population is made up of a wide range of molecules, each of which is uniquely structured to fit onto a specific type of molecule, such as the external molecules on the bacterial cell’s surface. After being exposed to a pathogen, such as the measles virus, and successfully clearing the infection, the body retains a memory of the antigens present on the virus, producing specialized antibodies to fight another infection by the pathogen. x000D_
The binding sites of these specialized antibodies have a specific shape that perfectly matches the antigens on virus particles. The antibody affinity of a binding site refers to the strength of the bond between one binding site on an antibody and one antigen on the invader. When looking at multiple binding sites on an antibody, the avidity, or functional affinity of the antibody, is the strength of the bond between the sites and the invader.
Antibodies and antigens are, at their most basic level, collections of atoms held together by chemical bonds. Non-covalent bonds hold an antigen to an antibody together, which means that the individual atoms and molecules do not share any electron particles and instead rely on weak electric attraction to hold together. Bonds that do not involve the transfer of electrons from one molecule to the next are usually weak, but a collection of many non-covalent bonds can be very strong. This happens in antibody-antigen interactions, and it’s what gives antibodies their affinity.
Antibody affinity strength is critical for accurate detection of invaders and subsequent infection clearance. Because the antigens are derived specifically from the target pathogen and engineered to be very recognizable, vaccines tend to produce strong antibody affinity to their antigens. Despite the benefits of strong antibody affinities, the body can benefit from weak antibody affinities, as they can allow the body to recognize new invaders that are similar to previously recognized invaders in some way.