WELL & GOOD

WHAT CAUSES THE BODY TO ATTACK ITSELF? THE REASONS ARE AS VARIED AS THE DISEASES THEMSELVES

Treating the enemy within

THE HUMAN BODY is a remarkable feat of design and engineering with the capacity for self-management and repair. Then sometimes, for no discernable reason, it attacks itself.

Most of the time, the body operates much like a well-ordered city. The infrastructure works well, public transport carts goods around, the sanitation department deals efficiently with waste and the defence department sees off foreign invaders. Peace and prosperity flourish, citizens are hale and hearty, and the trains run on time.

Then over-zealous soldiers within the body start to place sinister significance on everyday events, deciding there are shadowy external threats and foreign agents who need to be eradicated. It’s the classic conspiracy theory; innocuous activities are viewed as threats and civil war breaks out with all the needless pain and suffering that civil wars bring. Welcome to autoimmune disorders.

Autoimmune diseases happen when the body’s defence system can’t differentiate between its own cells and foreign ones, causing it to attack normal cells mistakenly. There are more than 80 types of autoimmune conditions. Most are relatively uncommon but collectively they affect one in 50 New Zealanders. Many strike the relatively young.

It’s only recently that autoimmune diseases have been grouped as a single category, in the same way as cancer or cardiovascular diseases; they are seen as different manifestations of the same underlying problem. A feature is that the female-to-male ratio is heavily skewed to females (10:1 in Hashimoto’s thyroiditis down to 2:1 in autoimmune haemolytic anaemia).

Why are women more vulnerable? There are a variety of theories, but it may begin with the female double X chromosome. Humans inherit two sets of 23 chromosomes - one set of 22 autosomes chromosomes plus an X or Y, the sex chromosomes. It’s possible that having a double XX doubles the risk of autoimmune disease-specific genes.

Pregnancy is another stress test for the female immune system; a woman has to carry a baby without her immune system attacking a technically “half-foreign” body (a foetus has genes and immune components from both parents).

What causes an autoimmune attack?

It’s not known for sure what causes the body’s immune system to turn on itself; because it’s so complicated, it’s hard to pinpoint a single cause. But the culprits include genetic susceptibility, environmental agents, an infection that triggers the immune system to react against specific body tissues, and reactions to chemicals and medications.

The most common autoimmune diseases are:

• Inflammatory bowel disease, Crohn’s, coeliac disease, pernicious anaemia, serious diseases of the digestive tract.

• Rheumatoid arthritis, a form of arthritis that attacks the joints.

• Psoriasis, a condition marked by thick, scaly patches of skin.

• Psoriatic arthritis, a type of arthritis affecting some people with psoriasis.

• Lupus, a disease that damages areas of the body that include joints, skin and organs.

• Thyroid diseases, including Graves’ disease, where the body makes too much thyroid hormone (hyperthyroidism), and Hashimoto’s thyroiditis, where it doesn’t make enough (hypothyroidism).

• Type 1 diabetes, which is strongly genetic and usually results from autoimmune attacks on the insulinproducing islet cells in the pancreas, leading to insulin deficiency. More than 34 million people worldwide suffer from diabetes mellitus, which usually occurs before the age of 30. The incidence of type 1 diabetes is rising by about four per cent per year, mostly among children. The most alarming increase has been among Finnish children, where rates are expected to increase by 60 per cent in the next 10 years. Most of the cases are in genetically suspectable children, but there also seems to be unidentified environmental causes.

Risk factors

Several theories point to an overactive immune system attacking the body after an infection or injury. It’s also understood that certain risk factors increase the chances of developing autoimmune disorders, including:

Genetics: Disorders such as lupus and multiple sclerosis (MS) tend to run in families.

Weight: Being overweight or obese raises your risk of developing rheumatoid arthritis or psoriatic arthritis. This could be because more weight puts greater stress on the joints or because fat tissue makes substances that encourage inflammation.

Smoking: Research has linked smoking to several autoimmune diseases, including lupus, rheumatoid arthritis, hyperthyroidism and MS.

Gastro-intestinal infections such as salmonella, shigella, yersinia and campylobacter can cause serious, longterm conditions.