One out of every 100 cells in your body is for defense against disease. So if you weigh 150 pounds (68 kg), 1-1/2 pounds (680 grams) of you are for self-defense.

10 Interesting Facts About the Human Immune System

1. It has a long-term memory.
   When the adaptive immune system encounters a pathogen, it creates specialized memory B and T cells. These cells can survive in the body for decades, recognizing the same pathogen if it returns and neutralizing it before you even feel sick—the core principle behind how vaccines work.
2. Fevers are an intentional feature, not a system failure.
   Your brain intentionally raises your core body temperature during an infection. Higher temperatures speed up chemical reactions, accelerating immune cell activity while simultaneously making the body a hostile, high-heat environment for reproducing viruses and bacteria.
3. It can trigger its own self-destruct mechanism.
   When immune cells called neutrophils encounter heavy pathogen loads, they perform NETosis. The cell explodes and expels its own DNA like a net, trapping and killing surrounding bacteria in a suicide maneuver that protects adjacent tissues.
4. Your eyes are an “immune-privileged” zone.
   The immune system is largely restricted from entering the eyes. Because inflammatory responses like swelling could permanently damage delicate optical structures and cause blindness, the eyes use specialized physical barriers and immunosuppressive fluids to manage pathogens locally.
5. Autoimmune diseases disproportionately affect women.
   Approximately 80% of all individuals with autoimmune diseases are female. Researchers attribute this primarily to the X chromosome—which carries a high concentration of immune-related genes—and the influence of estrogen on immune response regulation.
6. Sleep deprivation rapidly shuts down natural killer cells.
   A single night of getting only four hours of sleep can reduce the activity of your Natural Killer (NK) cells—the front-line defenders against virally infected and cancerous cells—by up to 70%.
7. It relies entirely on a secondary plumbing network.
   The immune system circulates white blood cells and drains cellular waste using the lymphatic system, a network of vessels containing clear fluid called lymph. Unlike blood, which is pumped by the heart, lymph has no central pump and relies on physical muscle movements and breathing to circulate.
8. Over-reaction can be far more dangerous than the infection itself.
   In severe cases of viral or bacterial infections, the immune system can experience a cytokine storm. This occurs when an uncontrolled positive feedback loop causes immune cells to release massive amounts of signaling proteins, leading to widespread tissue damage, organ failure, and systemic inflammation.
9. It kills thousands of potential cancer cells every day.
   Through a process called immune surveillance, T cells and NK cells constantly patrol the bloodstream and tissues, identifying and destroying mutated or abnormally dividing cells before they can establish tumors.
10. Stress hormones actively dissolve immune tissue.
    Sustained high levels of cortisol (the body’s primary stress hormone) suppress immune function by causing the thymus gland—where T cells mature—to temporarily shrink, reducing the production of new immune cells during periods of chronic strain.

Pictured above: Anthrax Virus

A mathematics major with a higher than average IQ estimated at 126, and seemingly normal in every other way, was referred to a brain specialist because his head seemed a bit larger than normal. The brain specialist was amazed to find that the student had an extreme case of hydrocephalitis, also known as “water on the brain.” His brain cavity was mostly filled with fluid, not neurons. The cortex, the main thinking part of his brain, was merely a coating one twenty-fifth of an inch thick on the inside of his skull!

The case was documented in the late 1970s by Dr. John Lorber, a professor of pediatrics at the University of Sheffield in the UK, and was featured in a renowned 1980 Science article titled “Is Your Brain Really Necessary?”

Here is how the details break down:

The Student: A 26-year-old student at the University of Sheffield was referred to the campus doctor because his head was slightly larger than average. Despite having no neurological issues or symptoms, he had a tested IQ of 126, held a first-class honors degree in mathematics, and was socially normal.

The Brain Scan: When Dr. Lorber performed a CAT scan, he discovered that the student had severe hydrocephalus (excess cerebrospinal fluid in the brain). Instead of normal brain tissue filling the skull cavity, fluid-filled ventricles occupied over 90% to 95% of the space.

The Cortex: The student’s cerebral cortex was compressed into a thin layer measuring roughly 1 millimeter thick (approximately 1/25 of an inch) lining the inside of his skull, rather than the normal thickness of 4.5 centimeters (1.75 inches).

How Is This Possible?

While the case sounds unbelievable, researchers attribute it to neuroplasticity. Because the fluid build-up occurred very slowly during the student’s early childhood development, his brain was able to adapt. The thin layer of remaining cortical tissue reorganized itself and compensated, taking over the functions that a normal-sized brain typically performs.

Current Status of the Student

Because Dr. John Lorber maintained strict patient confidentiality, the student’s identity was never publicly revealed, so there are no public updates on his current personal life or career.

However, medical history does tell us a few key details about how his story unfolded:

• Shunt Treatment: After the initial brain scan revealed his severe hydrocephalus in the late 1970s, Lorber installed a shunt (a small valve and tube system) to drain the excess fluid from his skull, relieving the pressure on his brain.
• Follow-up Health: Reports from the time indicated that he tolerated the procedure well, maintained his high intellectual ability, and went on to live a normal, healthy life.
• Ongoing Academic Debate: The student’s case became a classic textbook case study in neurology regarding neuroplasticity—the brain’s ability to compress, adapt, and reorganize itself when tissue damage or pressure occurs slowly over time.

While the individual stepped out of the spotlight to live a quiet life, his case remains one of the most famous examples in modern medicine of how remarkably adaptable the human brain can be.

Shown above: More common degrees of hydrocephalus