One might even say that forensic serology is all about antigens and antibodies , but that is the domain of immunology. In forensic law, blood has always been considered class evidence, but the potential exists for individualized blood typing, and even today, forensic serologists can provide testimony with some strong probability estimates linking a single individual, and that individual only, to a bloodstain. Consider that identical twins may have the same DNA profile but completely different antibody profiles, and you begin to see how promising the field of forensic serology really is. Most people are only familiar with the Rh factor, which is technically the D antigen. There are more than 256 antigens, and 23 blood group systems based on association with these antigens.
Antigens are chemical structures attached to the surfaces of red blood cells.
A basic principle of serology is that for every antigen, there exists a specific antibody. You are essentially determining blood type by injecting the worst possible poison into someone's blood sample to see what happens. Various extracts can be obtained from plants and seeds to create antiserums that clot type O blood, for example, somewhat selectively. The most commonly used types of antiserums used for this purpose are called lectins . The possibility of individualized blood types is based on the typing of proteins and enzymes.