Actin is a protein found in the cytoskeleton of all higher organisms and is involved in cell movement. Antibodies can react against actin, and there are three main groups in vertebrate cells. Actin antibodies are used in laboratory research and can be associated with autoimmune diseases. They are also used as controls in experiments and in cell biology studies.
Actin is a globular protein found in all higher organisms. It makes up a significant part of the cytoskeleton – or backbone of the cell – and is involved in cell movement. Antibodies are immune system responses to an antigen, which is usually a foreign object. Each individual organism can have millions of antibodies that react against different antigens. In some cases, such as autoimmune diseases, the body produces antibodies against its own cellular components.
An actin antibody is one that reacts against one of the forms of actin, which is very similar between different species of organisms. Its active form is as filaments. This is how it comprises part of the cytoskeleton and is involved in helping cells and muscles to contract. There are three main groups in vertebrate cells: alpha, beta and gamma. Alpha actin is generally found in muscles. Beta and gamma actins are found in most cell types.
An actin antibody typically falls into two categories of interest. The first are those antibodies produced in animals for use in laboratory research. The other category is autoimmune diseases in which an anti-actin antibody is man-made.
An example of the latter category is a smooth muscle antibody. The presence of this type of human antibody is characteristic of people with type I autoimmune liver disease, a chronic liver disease. Its presence is used as part of the diagnosis of the disease. Patients with hepatitis also have antibodies against smooth muscle. These types of antibodies are directed against a type of alpha actin, known as smooth muscle actin.
Another autoimmune disease associated with an actin antibody is celiac disease. The presence of these antibodies in the blood has been found to reliably correlate with intestinal damage in these patients. Celiac disease is caused by a reaction to a gluten protein in wheat, which disrupts the absorption of nutrients in the small intestine.
Experimentally, an actin antibody is often used as a control for experiments using antibodies. Since actin is structurally similar between species, one can be fairly sure that an actin antibody from one species will react with another. Beta-actin loading controls ensure that the same amount of sample has been loaded into each lane of a protein gel. This is used during electrophoresis, where you separate proteins by passing an electric current through a gel. The proteins are then transferred to a membrane and probed with antibodies in what is called a Western blot.
Fluorescently labeled actin antibodies are used in many cell biology experiments that study the movement of actin in the cytoskeleton and internal cellular structures, such as vesicles. Such actin antibodies can be monitored with specialized microscopy known as immunofluorescence microscopy. Because so many activities of the cell require actin, these types of experiments are performed in a wide variety of cell biology disciplines.
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