Summary & Study Guide - Eat to Beat Disease (eBook)

Chapter 5

Immunity

Our immune cells have receptors that can differentiate between friends and foes, including cancer cells. They are always on standby. When they spot signs of cancerous growth, they call on special cancer-killing immune cells to wipe out the abnormal cells before they cause problems. Sometimes, cancer cells dodge our immune system by camouflaging themselves to fool the immune cells. Other times, diseases or medications weaken the immune system so cancer cells can grow.

You can take many steps to safeguard your immune defenses. Exercise, proper sleep, proper diets, and lowering, and reducing stress all help your immune system stay healthy. Certain foods can boost your immune system to help it fight diseases. Other foods can help calm the immune system when it is overactive, as in autoimmune diseases.

Early Efforts at Immunity Boosting

Outbreaks of smallpox decimated the society during the reign of Chinese Emperor Kangxi (1661–1772). To protect his family and soldiers, Kangxi ordered imperial doctors to take scabs from the dried pox of people dying from smallpox and place them into the noses of his family and soldiers. This gave the recipients an immunity to the disease. This technique of variolation led to what is today called vaccination.

The first vaccine against smallpox was invented by the English doctor Edward Jenner in 1796. Over the next two hundred years, medical researchers have developed vaccines against other deadly diseases like polio, tetanus, rabies, chickenpox, mumps, cholera, diphtheria, and hepatitis. Through a global vaccination program organized by the World Health Organization, we have eradicated smallpox In 1980.

Anatomy of Immune Defense

Our immune defense system comprises four sites:

• Bone marrow is the spongy material in the hollow areas of your bones. It produces all the immune cells in your body.

• The thymus gland is the organ behind your breastbone. It is home to special immune cells called T cells. This gland is where young T cells from the bone marrow go to mature.

• The spleen is a fist-size spongy sack behind your stomach on your left side. This is where immune cells called B cells make antibodies.

• The gut is home to the microbiome, which influences the immune system.

Soldiers of Immunity

Immune cells are also called white blood cells. The three major types of white blood cells are T cells, B cells, and natural killer (NK) cells. T cells have three subtypes: helper T cells, cytotoxic T cells, and regulatory T cells (Tregs). Other immune cells include macrophages, mast cells, and dendritic cells.

All white blood cells originate from hematopoietic stem cells in the bone marrow. Therefore drugs like chemotherapy, which damages bone marrow cells and circulating white blood cells, lower your immunity. Studies have shown that diet can influence the production of immune cells in the bone marrow. Fasting two to four days in a row forces the body to go into cycling mode, which gets rid of older, worn-out immune cells. When you eat again, it jump-starts the hematopoietic stem cells in your bone marrow to regenerate fresh immune cells thus rebuilding the immune system.

A Two-Part Immune System: Fast and Slow

Innate Immunity: Master of Inflammation

The innate immune system is swift acting, responding to an invader using the same weapons. It is the first responder to any invasion of your body using weapons that include physical, chemical, and cellular components. It responds to tissue damage or foreign invasion by creating inflammation, which is accompanied by swelling, pain, redness, and increased warmth. White blood cells release chemical signals called cytokines that trigger other immune cells to charge into battle, including natural killer (NK) cells. NK cells can distinguish abnormal from normal cells. If they spot an abnormal cell, they use specialized proteins to kill it.

Under normal circumstances, the innate immune response is short-lived and subsides within a few days. When it’s time to turn down the inflammatory response, the immune system shuts down the immune response to prevent it from damaging normal cells.

Adaptive (Acquired) Immune System

The adaptive immune system is slower acting but more sophisticated. It takes about a week to assemble its defenses, using weapons fine-tuned to knock out specific targets on invaders. Moreover, it has a permanent memory of the invaders it destroys. Once the adaptive immune response learns how to fight off disease, it protects you for the rest of your life.

From the battlefront where enemies are invading, special cells called dendritic cells record data about the unique protein fingerprints of bacteria, viruses, and cancer cells. They present these fingerprints to the proper immune cells that will find, mark, and then kill the invader.

Adaptive immunity uses two strategies to defend the body. The first strategy, called cell-mediated immunity, uses T cells to attack invaders. There are three types of T cells.

• Helper T cells orchestrate an immune attack against invaders by signaling to other cells what to do. Some signals direct the troops to attack, while other signals instruct B cells to make antibodies against the invader.

• Cytotoxic T cells are combat fighters that destroy bacteria, infected cells, or cancer cells.

• Regulatory T cells, or Tregs, shut down the immune response when the battle is over by releasing chemical signals to suppress helper T cells and cytotoxic T cells.

The second strategy uses antibodies to attack the intruder. Each B cell is bristling with up to two hundred thousand antibody receptors, made to match up with abnormal antigens from bacteria and viruses. The antibodies hit the invaders and mark them for death, and phagocytes swarm in to destroy them. Because it takes seven to ten days to make antibodies for new invaders, this defense has a slow response time.

Failed Immunity and Disease

Acquired immune deficiency syndrome (AIDS) is the best-known example of a life-threatening collapse of immunity because of an HIV (human immunodeficiency virus) infection. HIV is a retrovirus that invades and destroys healthy human T cells. Without adequate T cells, our body’s ability to detect and kill all invaders drops, increasing the risk for catastrophic infections and cancer. Effective treatment can reduce the level of the virus in the blood to zero, allowing an HIV-infected individual to live an otherwise normal life.

Our gut microbiome can influence our immune defense by sending signals to “turn on” or “shut down” immune defenses. If certain gut bacteria are missing, or deficient, it weakens our immune system. Unhealthy foods can weaken our immune response by interfering with the ecosystem of the microbiome, causing miscommunication between the gut and our immune cells.

Weakened Immune Conditions

A broken-down immune system can open the door to life-threatening infections. Cancer can also take root because an ineffective immune system cannot detect cancer cells. Traditional cancer treatments based on high-dose chemotherapy and radiation weaken the immune system even more. They target cancer by destroying fast-growing cells in the body, which include our immune cells and the cells in our hair, nails, skin, mouth, airway, and intestines. These drugs will stop their growth, resulting in all the side effects plus a weakened immune system.

New immunotherapy cancer treatments do not rely on toxic or targeted drugs to kill cancer cells. They encourage our body to rid itself of cancer. One type of immunotherapy, called checkpoint inhibitors, blocks the cloaking proteins that cancers use to hide from the immune system. This allows the patient's own immune system to see the cancer and then try to destroy it.

Another type of immunotherapy, called CAR-T cell therapy, collects T cells from the patient, and then reprograms those T cells to target cancers. CAR-T cell therapy is effective in treating lymphoma and leukemia.

Infections by certain viruses can also destroy the body’s ability to mount an adequate immune response. HIV causes AIDS. Human papillomavirus (HPV) increases the risk of cervical cancer, penile cancer, and cancer of the mouth and upper airway. Hepatitis B and Hepatitis C are other infections that compromise the body’s immune system can lead to liver cancer.

Other diseases like Type 1 and type 2 diabetes can make an individual more vulnerable to infections. Obesity impairs the immune response by creating a chronic low-grade state of inflammation in the body. In these conditions, consuming foods that enhance immunity would be beneficial.

With certain inherited diseases, however, where the immune cells are defective and unable to function, dietary factors are unlikely to help. Some of these conditions with life-threatening immune defects include ataxia telangiectasia, Chédiak–Higashi syndrome, and severe combined immunodeficiency disorder.

Overactive Immune Conditions

When an overactive immune system is active in the wrong place at the wrong time and destroys the body’s own tissues, it results in autoimmune diseases....