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What is Immunoglobulin M?

Instructor: Darla Reed

Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

In this lesson you will discover what Immunoglobulin M is, where it is found, and some of its functions. You will also learn why its presence is important in your body.

What is an Immunoglobulin?

When you get sick there's all kinds of medicine you can take, depending on if you've got something like the flu, allergies, or something even more serious.

Your body is ready with its own form of medicine, the immune system. The immune system works to protect you from disease and is made of many different components. One of these components is called a B-cell. B-cells come from the bone marrow and produce what are called antibodies, or immunoglobulins that are used in fighting off agents of disease.

B-cell with Ig
B-cell example

Disease agents want to sabotage our body, take it over and use it for their own purposes. Immunoglobulins (Ig) are Y-shaped proteins that attach to and attack agents of disease.

Ig Structure
Ig structure

The ends of the Y are what attach to disease agents and the kind of stem is how Ig's are classified. There are five main types of immunuglobulin: IgA, IgD, IgE, IgG, and IgM. Just as the type of medicine you take depends on what you've got, the type of Ig that responds to a threat depends on the disease agent.

What is Immunoglobulin M?

Immunoglobulin M (IgM) is a class of Ig that is the first Ig expressed on B-cells and the first responder to disease agents. B-cells can make Ig that attaches to its surface, or it can secrete it, leaving it free to move around the body, usually in the blood plasma or lymph (fluid between tissues).

IgM can be secreted or attached.
Secreted and attached IgM

When a B-cell with attached IgM encounters a disease agent, it can change to show or secrete another class like IgG.

B-cells can change classes after encountering disease agents.
B-cells class switch after encountering disease agents.

Structure of IgM

Have you ever seen those books that unfold? At first it looks like all the other books, but then you open it up and not only can you read it, but it turns into cool shapes that you couldn't do with a regular book. IgM structure is like the unexpected unfolding book.

Like all other Igs (regular books), it's Y-shaped and the ends of the Y bind specific and unique aspects of disease agents.

IgM structure.
IgM structure

But when it's secreted, IgM does something different. It can form a pentamer, or a group of five. Think of sky divers linked up by their arms and falling through the air.

IgM forms a pentamer.
IgM forms a pentamer like falling skydivers.

In order to form a pentamer it must have a special attachment called a J-chain. This J-chain allows the five different IgMs to link up.

Occasionally IgM will fly solo, or form hexamers (groups of six). When it does so, it doesn't use the J-chain.

When a group of IgM finds and binds a disease agent, its shape can change from that of a group of sky divers to more of a spider- with the arms of the Y connected to the disease agent and the stems of the Y still together.

IgM can form a spider-like structure when bound to disease agents.
IgM binds disease agents and forms spider like structure.

Because of its group structure, IgM can be polyreactive and have a high valency. Polyreactive just means it can bind a variety of components, including nucleic acids and carbohydrates.

IgM can be polyreactive.
IgM can be polyreactive.

Having a high valency means IgM can bind many times to the same disease agent. Thus, it binds well to repeating patterns, like those found on virus particles, DNA or red blood cells.

IgM can have high valency.
IgM can have high valency.

Functions of IgM

IgM is one of the first Ig to respond to disease agents like bacteria. It's main function is to make sure bacteria and the like are destroyed A.S.A.P., before they can cause damage.

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