Antigens

Background

Antigens are large molecules such as chemicals, toxins, drugs and foreign particles on the surface of cells, bacteria, fungi, viruses and non-living substances.  The immune system detects antigens and releases antibodies that recognize and initiate destruction of foreign substances that contain antigens.  Antigens can be produced by bacteria or viruses within the body, as well as by your own tissues.  The recognition of pollen or molecules from food results in an allergic response by the body.  Upon entering a cell, an antigen is coupled to a histocompatibility complex and presented on the surface of the cell to be recognized by antibodies.  Each antibody matches an antigen like a key to a lock.  The fit of the antibody can be precise, while other times it is like a skeleton key and fits almost anything.  The role of antibodies is to target an antigen and mark it for termination.

Antibodies reside in the body’s fluid and are gamma globulin proteins.  The body uses antibodies to identify and neutralize foreign objects in the body, such as viruses or bacteria.  This mechanism is like a built-in antibiotic for the immune system.  Antibodies are classified as a family of large molecules known as immunoglobulins.  Globulins consist of polypeptide chains or amino acids.   Each antibody is constructed of 2 light chains and 2 heavy polypeptide chains that form the arms of a “Y” shape.  These arms are antigen specific and vary from one antibody to another.  One type of antibody is called a monoclonal antibody which is are commonly used as reagents for diagnostics and research due to their recognition of a single epitope.

Other types of antibodies include: 1) Autoantibodies – rather than fighting foreign antigens, autoantibodies attack the body’s own cells, and 2) Antinuclear antibodies – a group of autoantibodies that attack structures inside the nucleus of the cell.

Therapeutic Antibodies

Introduction of antibodies to human therapy is slow, although there have been some recent advances in approved medicines.  Monoclonal antibodies present a highly specific therapy that can identify and affect cancer cells specifically.  However, the size of an antibody limits their efficiency and penetration in vivo for the treatment of different types of cancer.

Monoclonal antibodies are created by combining single antibody forming cells with tumor cells that are grown in culture.  The new cell is called a hybridoma cell and each one of the new cells produces a large quantity of identical antibody molecules.  Growing these cells in culture makes it possible to produce large quantities of identical antibody molecules.  One problem identified with in vivo animal testing was that the production of antibodies resulted in the animal antibodies and the human immune system frequently attacked them just as they would any foreign substance entering the body.  Scientists found a way to bypass this problem by replacing some of the animal content with human content in a fusion process. The result is antibodies that are approximately 65% human.

Currently there are numerous antibody therapeutics in clinical trials and approved as standard of care therapies.  These include monoclonal antibodies such as ipilimumab, pembrolizumab and nivolumab.

Most efficient animal siRNA delivery kits are: Nanoparticle- and liposome-based siRNA In Vivo Transfection Reagents.