Natural antibodies serve as one of the immune system’s primary sentinels. These large Y-shaped molecules carry two variable domains (the Fab regions), which are designed to recognize and bind to specific antigens that are seen as threats. The targeted antigen might be a protein found on a pathogen or a protein marker found on malignant or infected cells. Antibodies also have an immune-stimulating domain (the Fc region) that helps to mount a broader immune response to threats flagged by antibodies.
Monoclonal antibodies are bioengineered molecules that are designed to target specific proteins involved in disease. Like natural antibodies, they are potent and highly selective in terms of the targets they engage. They also tend to stay in the body longer than most other medicines, so in general, they need to be dosed less frequently. Antibody drugs can be used against targets that are outside cells or on the cell surface, but because of their size, they generally can’t reach targets inside cells.