Immunoglobulin A (IgA)

Immunoglobulin A (IgA) is a type of protein (an antibody, to be specific) that your body makes to help prevent germs (pathogens) and toxins from getting into your cells. It’s found mostly in your body fluids and mucous membranes, like your respiratory and digestive systems. “Ig” is short for immunoglobulin, which is another name for antibody.

IgA works a bit like a security guard who catches harmful invaders and escorts them out of your body. Like all antibodies, IgA antibodies have a unique shape that allows them to recognize bacteria, viruses, toxins and other potentially harmful substances. This shape fits one specific antigen — molecules that label a cell or an organism as part of your own body (“self”) or foreign and potentially dangerous (“non-self”).

When an antibody encounters an antigen that it fits — like on the surface of a virus or bacterium — it tells your immune system that it’s found a potential problem. Your immune cells can then take action to eliminate the harmful substance by flushing it out of your body or destroying it altogether.

Where is IgA found in your body?

Specialized areas of immune cells called mucosa-associated lymph tissue (MALT) create most IgA antibodies. They live in your body fluids, including:

• The lining of your mucous membranes (mucosa) — especially your digestive tract
• Saliva
• Tears
• Sweat
• Breastmilk — antibodies in breastmilk can be passed to a baby through breastfeeding

IgA found in your body fluids is called secretory IgA (SIgA). A small amount circulates in your blood (serum IgA).

Types of IgA

There are two types of IgA (IgA1 and IgA2) — they have slightly different structures. While you can find both types of IgA in your blood and other body fluids, most of your serum IgA is type 1. Most of your secretory IgA is IgA2.

What do IgA antibodies look like?

IgA antibodies are too small to see with the naked eye — so you won’t see them on a tissue when you blow your nose. But if you looked at them under a powerful microscope, you’d see “Y”-shaped proteins.

You can think of immunoglobins like a two-pronged fork, ready to spear anything they recognize as harmful that enters your body. Their shape allows them to read the antigen labels on substances they encounter with the forked end (receptor or Fab region), while the straight end can attach to immune cells.

IgA can be monomeric (one “Y” shape) or dimeric (two “Y” shapes joined at the straight end).

What does immunoglobulin A do?

Immunoglobulin A works with other parts of your immune system to protect you from potentially harmful substances in your body. IgA functions mainly through immune exclusion — that is, it sticks to germs and ushers them out of your body. It’s like telling the invaders: “You don’t have to go home, but you can’t stay here!”

Steps in immune exclusion include:

• Neutralization: An IgA antibody attaches (binds) to a pathogen or toxin and prevents it from attaching to and entering your body’s cells. This can also recruit immune cells to destroy them (opsonization).
• Trapping: IgA can trap harmful substances in your mucus or another body fluid. Dimeric IgA can latch on to many areas on a large bacterium or to multiple bacteria at one time.
• Clearance: Processes like mucociliary clearance in your lungs (hairlike structures sweeping the mucus up and out) and peristalsis in your digestive tract move the fluid (and the germs with it) out of your body. This usually means you poop the germs out or they come out of your nose in your snot.

IgA also has other important jobs, including:

• Maintaining homeostasis: IgA maintains the right amount of healthy bacteria in your mucous membranes while protecting you from harmful bacteria.
• Controlling allergies: IgA blocks allergens from causing inflammation in your respiratory and digestive tracts. People with low levels of IgA are more likely to have allergies and asthma.

What are normal IgA levels?

Normal IgA for adults is 60-400 mg/dL. This varies by lab and by your age, so be sure to check the reference range on your test results.

What diseases cause high IgA?

Causes of high IgA include:

• Chronic infections
• IgA nephropathy
• Wiskott-Aldrich syndrome
• Chronic liver disease
• Multiple myeloma
• Lymphoma
• Inflammatory or autoimmune diseases
• Obesity

What causes low IgA?

Some people naturally have a low level of IgA without a known cause. Conditions that affect your immune system’s ability to make antibodies and other immune cells can also cause low levels of IgA. These include:

• Selective IgA deficiency
• Hypogammaglobulinemia
• Ataxia-telangiectasia
• Waldenström macroglobulinemia

What are the symptoms of conditions that affect IgA?

Low levels of IgA — or even no IgA — often cause no symptoms and don’t need to be treated. But some people with low levels of IgA antibodies get frequent bacterial, viral and parasitic infections in their respiratory and digestive tracts. Examples include:

• Sinusitis
• Pneumonia
• Bronchitis
• Cytomegalovirus (CMV)
• Thrush
• Ear infections (otitis media)
• Gastroenteritis — especially bouts of diarrhea

Additionally, having low levels of IgA can increase your risk for:

• Autoimmune diseases — most commonly, celiac disease, lupus, inflammatory bowel disease (IBD) and rheumatoid arthritis (RA)
• Asthma
• Allergies

What tests are there for IgA?

Your provider can order immunoglobulin tests to check your levels of IgA and other antibodies. This is a blood test that can help diagnose immune system diseases and infections.

Are there treatments for high IgA levels?

There aren’t any specific treatments for high or low IgA levels. But if you have an underlying condition that’s causing changes in your IgA levels, a healthcare provider can often treat that specific condition.

Antibiotics usually treat frequent infections caused by low levels of IgA. Sometimes, you might need immunoglobulin replacement therapy or intravenous immunoglobulin (IVIG) treatments to give you additional antibodies that help you fight infections.