The primary difference between an antibody and a protein is that, while all antibodies are proteins, not all proteins are antibodies. Proteins are a general category of large molecules that serve as both structural and functional units for all living organisms on Earth. They are also the repository of 20 essential amino acid molecules in plants and animals that are necessary for human survival, but which the human body cannot manufacture on its own from other chemical precursors. Antibodies are a special type of Y-shaped protein that act as part of the immune system, which contain special binding receptor sites for antigen sites on viruses and bacteria, from which such organisms reproduce themselves. When antibodies are present in significant numbers, they inhibit the reproduction of viruses and bacteria in the body by binding to antigens, and trigger other immune responses to ensure health as well.
Another key feature of both an antibody and a protein that is instrumental in their function is how the molecules are folded, or shaped, as this affects their ability to bind to other molecules and interact favorably in the cellular environment. While an antibody and a protein can have different chemical structures, their fold architecture can be similar in some cases, which directly impacts the role that they play at any one time in the body. Current databases as of 2011 have identified only a limited number of actual fold patterns that occur in nature, though, theoretically, there could be millions of different combinations. Estimates are that there are between 1,233 and 1,393 fold patterns for an antibody and a protein. All antibodies take on a unique Y-shape, however, with specific amino acid receptor sites in the upper part of the Y, where both branches of this region can bind to two separate antigens simultaneously to disable them.
A key difference between an antibody and a protein is also the region from which they are produced. While protein synthesis is a natural result of combining amino acid sequences in various types of cells from deoxyribonucleic acid (DNA), antibodies have more restricted production methods. Antibodies are often referred to as immunoglobulins for their binding role in the immune system and these molecules are usually only produced by B-lymphocyte or B-cell structures, also known as white blood cells or plasma cells, located in bone marrow.
The general classification for an antibody and a protein also varies. While at least 100 different types of protein molecules exist and they serve numerous molecular functions from facilitating motor activity to DNA catalysis, antibodies are either monoclonal or polyclonal. Monoclonal antibodies are able to bind to only one specific antigen and are produced naturally in the body in response to foreign invaders. Polyclonal antibodies, on the other hand, are harvested from the blood of immunized animals, and can be engineered to attach to a wide range of antigens.
Organisms naturally stimulate antibody production to protect themselves from infection, but medical science is also heavily involved in creating research antibodies, and large antibody catalog lists now exist where laboratories can order the antibodies that they need for particular research interests. The number of polyclonal antibody suppliers worldwide numbered at least 180 companies as of 2011, many of which have lists of over 20,000 different antibodies available for sale and shipment, including some monoclonal antibodies as well.