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What is Immunoglobulin A?

Instructor: Catherine Paul

Catherine has taught high school science and has a master's degree in biology.

Learn about the most highly produced antibody in our system, immunoglobulin A (IgA). Discover how IgA maneuvers into body cavities, acting as an important defense against bacteria and viruses.

Immunoglobulin Classes

When foreign bodies invade, our immune system has to act quickly. Luckily, it has a swarm of antibodies ready for the job. These antibodies are proteins specifically designed to attach to invaders like bacteria, viruses, and toxins. Antibodies are precisely designed to bind to specific invading proteins, or antigens, that the bacteria, viruses, or toxins display. There are five groups of antibodies that our system produces: immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin E (IgA), immunoglobulin M (IgM), and immunoglobulin D (IgD). Today we're going to be focusing on IgA, but we'll still be exploring some basic principles of immunoglobulins in general.

Basic IgA Structure

Imagine immunoglobulins shaped like a two-pronged fork, and using the tip of the fork to attach to a foreign antigen in order to disable it. This Y-shaped structure is shared among all classes of immunoglobulins, including IgA. It contains two identical heavy chains and two light chains. You're right if you guessed that the heavy chain weighs more and is larger than the light chain. The heavy chain extends along the entire length of the Y structure, whereas the light chain binds to the heavy chain on the exterior of the prongs of the Y shape.

Heavy and Light Antibody Chains
Heavy and Light Antibody Chains

IgA Secretion

It is important that all immunoglobulins cover all the bases throughout our body; therefore, there's secreted immunoglobulin and membrane-bound immunoglobulin. Secreted immunoglobulin is exported from the bloodstream to other places, such as the nasal cavity. Membrane-bound immunoglobulin is attached to the surface of an important cell of the immune system called the B cell.

Often, IgA is secreted to external sites, such as saliva, breast milk, tears, and the mucus of our digestive and bronchial tracts. This secretory IgA is a primary defense against invaders that would enter though these cavities. IgA is particularly important for newborn infants, whose health benefits from this immunoglobulin as it is passed on through breast milk. The antibody acts as a barrier between bacteria and the baby's digestive system by binding to the microbe and stopping further passage into the body's tissues.

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