A macrophage can eat 100 bacteria, on average, before it's exhausted

Bacteriophages—viruses that infect bacteria before multiplying within them—exist on Earth in numbers greater than all other living organisms combined.

Trillions of bacteria, viruses, fungi, protists, and archaea live in our guts, producing a wide range of molecules, hormones, and more—underscoring the immune system's pivotal role in the microbiota-gut-brain axis.

Chronic inflammation can cause cellular damage and could lead to cancer

Over time, this cellular defense system can inadvertently damage cells and tissues when it's in this heightened alarm mode over a prolonged period. This occurs because, when immune cells are sent somewhere without a true target, they may attack healthy cells and tissues.

There are up to 100 trillion microbes in the gut, and maintaining the relative balance in this ecosystem is important for our health.

An interactive dive into the immune system

Our bodies are equipped with an incredible system able to fight off invasive pathogens to protect us from illness. The complicated system includes lymph nodes, the spleen, bone marrow, and even the tonsils. But this same system can turn against itself, a condition known as autoimmune disorders. Follow along with this thorough, engaging explainer on the human body's defense system.

Some animals, including certain tropical ants, have little or no microbial populations in their gut, upending the idea that all animals rely on this ecosystem to help maintain their health and proper functioning.

These cells 'taste' danger, trigger immune responses

Taste receptor-coated tuft cells are found throughout the body, where they communicate with and take part in a growing list of biological processes. In the intestines, these taste receptor-studded cells can sense byproducts of parasite metabolisms. This causes the taste receptors to release chemicals that alert the immune system, order nearby goblet cells to produce mucus, and trigger muscle contractions in attempts to launch the parasites from the intestines.

Some mosquitoes are key pollinators—and eat disease-carrying mosquitoes.

Autoimmunity is when the body attacks itself, causing inflammation

Inflammation is the body's way of healing itself, and acute inflammation saves our lives when we have injuries or infections. It increases blood flow to the affected areas to bring immune cells to fight off invaders. This often results in short-term swelling, redness, and pain.

The immune system is in a constant fight to detect and eliminate cellular mutations.

The gut microbiome may play a major role in autoimmune disease and symptom flare-ups

Certain unhealthy foods can promote gut bacterial growth and inflammation in the lining of the gut, potentially disrupting its lining—leading to a leaky gut that may allow pathogens to dribble out into the bloodstream, fueling further inflammation that can both cause disease flare-ups and set the stage for future disease development.

Microbes are essential to creating the many varieties of cheese, influencing texture and taste

Microbes break down proteins and fats and produce compounds with distinct tastes. These microbes can include bacteria (like the one used to give Swiss its trademark holes), molds (like the ones that give blue cheese its distinctive veining), and countless other tiny organisms.

How bitter taste receptors help guard against infection

Receptors for "bitter" tastes evolved to detect potentially harmful plant chemicals, such as nicotine. The receptors also trigger bacteria-fighting responses, including waving hairlike projections to bat away bacteria, ordering the release of bacteria-killing nitric oxide, and calling for antimicrobial protein reinforcements.

Short-term cortisol spikes can boost the immune system

Elevated acute levels can enhance the immune system's ability to fight off infection or respond to injury. Chronic heightened cortisol levels, however, can lead to inflammation that harms cells and tissues over time.

Most cells undergo programmed, controlled death

In the average adult human, apoptosis occurs in 50 billion to 70 billion cells daily when proteins managing a cell's life cycle send signals that the cell is damaged, causing it to break apart into smaller pieces that are consumed by white blood cells. The consumption prevents damage from spreading via cell division.

Researchers generally group gut bacteria into six different categories, with varying amounts of these microbes residing in different parts of the digestive tract.

A quick video on how your immune system works

Explore how your immune system's vast network of cells, tissues, and organs coordinate your body's defenses against bacteria, viruses and toxins with this 5-minute TED talk video.

The gut microbiome—a complex community of up to 100 trillion microbes—has a changing composition, influenced by our life stage, diet, medications, environment, and other factors.

Lining up every microbe on Earth would stretch to about 105,000 light-years

There are about 10²⁷ such organisms on the planet, many of which are adapted to produce energy through uncommon reactions in unconventional environments, such as within rocks or near volcanoes on the ocean floor. Studies of these organisms have reframed astrobiologists' search for life beyond Earth by broadening the parameters under which life can exist.

In 2026, University of Cambridge researchers reported that a group of gut bacteria called CAG-170 may be a key marker of good health, occurring far more often in healthy individuals and less commonly in people with chronic diseases.

Fevers are an immune response to create hurdles for pathogens

Substances called pyrogens prompt the brain to raise the body temperature to levels where bacteria and viruses struggle to survive. The higher temps also support immune cells fighting off the invaders.

Specific gut microbiome 'fingerprints' are associated with cancer recurrence, with up to 94% accuracy.

Gut microbiome rewrites may help reduce allergies

Researchers are investigating different strategies to determine if one day they could give people a combination of gut microbes to set them up for fewer allergies. In animal research, scientists have already prevented severe allergic responses in allergy-prone mice—supplying them with gut microbes from healthy, non-allergic human babies.

Superbugs evolve defenses against medication, then share them with neighbors

One reason antibiotic resistance spreads so quickly is that bacteria have multiple mechanisms allowing them to share genetic material. This short video offers a concise explanation for each of these mechanisms, and animation that helps viewers understand how antimicrobial resistance can quickly spread from one organism to another.

The inner life of a cell

White blood cells are responsible for protecting the human body from infection. This video uses biophysical data from Harvard researchers to accurately demonstrate what goes on inside one white blood cell as it works within the immune system.

Bacteria rapidly evolve (and share) new defenses against drugs they encounter

Unlike humans, bacteria rapidly make genetic changes in response to their environment, including creating defense against antibiotics. Furthermore, these defenses are passed on to their future generations and can even be shared with neighboring bacteria through horizontal gene transfer.

Gut bacteria are evolving and can acquire as many as 100 new genes per year, on average.

CRISPR-Cas systems act as genetic memory banks for defending bacterial cells

When viruses called phages inject DNA into bacteria, some bacterial species store bits of this DNA in their own genomes. This allows them to recognize and destroy the same virus if it attacks again.

There's no definitive test for inflammation, or a baseline for what's considered normal

Existing tests can pick up proteins that indicate an immune response—in particular C-reactive protein, which the liver produces when the body's stressed—but that won't tell you why there's inflammation nor if it's chronic or acute inflammation. (Some users may experience a paywall.)

How microbes limited the damage and helped clean up the Deepwater Horizon oil spill

A bloom estimated to contain about 100 sextillion microbial cells broke down much of the 4.1 million barrels of spilled crude oil into nontoxic compounds in what was one of the most significant bioremediations of a human-made disaster. The microbes involved acted similarly to the first patented genetically modified organism in US history: an oil-eating bacterium engineered in 1971.

How the microbiome affects your health

The gut microbiome is so influential to overall human health that some researchers consider it a separate organ. Its conditions, influenced by environmental and lifestyle factors such as medication and exercise, contribute to immunity, metabolism, inflammation, medical treatment efficacy, brain development and function, and the development of disorders and diseases, including asthma, depression, inflammatory bowel disease, and Alzheimer's.

How Nobel Prize-winning research unraveled why the immune system doesn't always attack itself

The 2025 Nobel Prize was awarded to scientists who discovered how immune system soldiers are typically stopped from attacking healthy tissue. The work furthered autoimmune understanding and cancer therapies.

Women typically have more robust immune responses than men

This difference helps women better combat infectious diseases, but this more turbo-charged response may also make women more vulnerable to autoimmune diseases by potentially priming their immune systems to overreact to their own cells and tissues and label them as invaders that must be destroyed. Roughly 80% of American women have autoimmune conditions.

Bacteria use chemical signals to communicate and coordinate with one another

Through a system called quorum sensing, bacteria produce and absorb compounds from their environment to identify allies or competitors and adjust their behavior accordingly. Some bacteria produce food-digesting enzymes only in the presence of similar bacteria, thereby preventing competitors from consuming their meal.

The adaptations of metallophiles and how they can be harnessed for bioremediation

These extremophiles have adapted to biomes with very high concentrations of metals and toxic chemicals by developing mechanisms to isolate these substances within cellular compartments and break them down into less harmful forms with specialized proteins. They have the potential to support the decontamination of metal-rich wastewater and soil, as well as the extraction of rare-earth metals.

Examining the potential of the emerging field of insect-based bioremediation

Also known as entomoremediation, the novel approach uses larvae and adult insects, including their gut microbiomes and associated enzymes, to extract or degrade pollutants. As of 2025, research has shown that black soldier flies can degrade a wide range of antibiotics, highlighting their potential for bioremediating antibiotic-contaminated organic waste.

Cells cannot grow forever due to escalating inefficiency in transporting chemicals

As cells get larger, their volume grows much faster than the surface area through which nutrients and waste products pass, creating a bottleneck that eventually causes cells to die. This forces nearly all organisms visible to the naked eye to comprise enormous numbers of smaller cells, such as the approximately 30 trillion found in the average adult human.

A 'buffy coat' is the roughly 1% of blood that includes multiple types of white blood cells and plays a key role in fighting off disease.

Bone marrow generates roughly 500 billion new blood cells each day.

Inflammaging is chronic low-level inflammation as we age, and it may be a key disease driver

The term refers to the idea that largely invisible but consistent low-level inflammation as humans age fuels chronic diseases and cellular aging. Inflammaging, this article says, is due to lifestyle factors like poor sleep, low levels of activity, and poor diet, acting in concert to cause cellular damage and trigger inflammation.

Measles attacks the body's immune system, leaving it vulnerable to secondary complications.

What is the immune system? A quick 101

Your body’s immune system is designed to protect you from infection. Find out more about how the immune system works with this quick overview and set of diagrams.

Superbugs could claim 1.9 million lives per year by 2050

The increased use of antibiotics combined with an aging population, is projected to result in an almost 50% increase in global deaths from antimicrobial resistance each year. At the same time, antibiotic use for livestock is expected to increase by 30% over the same time frame.

Inflammaging appears to differ across global populations

Chronic, low-grade inflammation linked to aging is a byproduct of our industrialized lifestyles, according to recent research. The work compared two industrialized populations with two Indigenous, non-industrialized populations in Bolivia and Malaysia, and found that inflammation levels in the Indigenous groups—unlike the industrialized ones—did not seem to differ by age.

Metabolism, a collection of chemical reactions at the cellular level, processes food and converts it into energy to power the body.

Large animals like giraffes and elephants have evolved unique cancer defenses.

Contributing to one in every three bites of food consumed by humans, bees are a keystone species because of their essential role as pollinators of about 80% of all flowering plants worldwide.

What is a microbiome (and why are they important)?

Jump to: What is the microbiome? How microbiota benefit the body The role of probiotics Can diet affect one’s microbiota? Future areas of research What is the microbiome? Picture a bustling city on…

Learn how monoclonal antibodies, which mimic the body's antibodies, can fight diseases like Ebola.

Superbugs are pathogens that have proved resistant to medications designed to combat them, rendering standard treatments ineffective.