What Is Your Immune System, Anyway?

You probably know that your immune system plays an important role in keeping you healthy, but there's so much more to this critical system that works as our defense against infection.

Here, two immunity experts break down the key parts of the system and what we mean when we talk about "strong" or "weak" immune responses.

Put simply: "The immune system is all the parts of the body that help to defend us against infection, whether by bacteria, virus, fungi, mold or parasites," Adam Lacy-Hulbert, PhD, who conducts research on immunity at the Benaroya Research Institute at Virginia Mason, tells LIVESTRONG.com.

The system is "a network of cells, channels and nodes" that work together, adds Cynthia Li, MD, integrative and functional medicine doctor and author of Brave New Medicine, a memoir about her path to healing her own autoimmune illness.

Let's take a closer look at these parts of a whole:

T Cells and B Cells

The immune system includes white blood cells called lymphocytes, and two types of these lymphocytes — T cells (thymus cells) and B cells (bone marrow- or bursa-derived cells) — play a role when something foreign threatens the body.

"The job of T cells is to recognize and kill cells that are infected," Lacy-Hulbert says. "The job of B cells is to make antibodies that are designed to bind specifically to viruses and bacteria, and to neutralize them to stop them from working."

Some of these B and T cells become memory cells; they remain dormant until they get the word that something they know how to fight (whether from experience with a vaccine or previous infection) has intruded.

"That immune memory you have can last for a lifetime," Lacy-Hulbert says, which is important for fighting off infection faster and allowing the body to recover more quickly.

Innate Cells

T cells and B cells are very important, but their laser-like focus can actually be problematic at times. "They don't know what to attack all the time," Lacy-Hulbert explains.

To balance this out, another part of the immune system — the innate system, which is composed of a different group of cells — acts as a kind of patrol, directing the B and T cells.

"Innate cells try to work out what's going on, go to lymph nodes, interact with T and B and tell them what the deal is and whether they need to neutralize or kill [what's triggering the immune system]," Lacy-Hulbert says.

Innate immune cells are messengers; if you get a cut on your skin and that cut gets infected, innate immune cells "send out an alarm" to signal a need for help, Lacy-Hulbert says.

Neutrophils and Monocytes

These innate cells recruit a host of other immune cells, called neutrophils and monocytes, which speed their way to the site of injury and fight whatever they find. Essentially, these are the workhorses of the immune system, Lacy-Hulbert says.

Neutrophils and monocytes are early-wave defenders. They work hard, but without much specific knowledge about the infection, so they can cause damage to host cells, stimulate inflammation and are often responsible for the pus that can form inside a cut.

These cells hold down the fort, so to speak, until those specialized T and B cells arrive to fight the infection in a specific way, if necessary.

This is a valid question, but it may not be the right one to ask. That's because a strong immune system isn't always a helpful one, Lacy-Hulbert says.

"If you have a strong immune system, you might fight infection better, but you might have a stronger response of that initial collateral damage — more inflammation than you actually need, more scar formation, maybe a wound takes longer to heal," he explains.

He believes that when we say "strong" immune system, what we really mean is a healthy immune system.

This answer isn't so clear cut, either.

"This is a debate and a problem we struggle with in immunology as a whole," Lacy-Hulbert says. "To me, a healthy immune system is one that makes good choices — it's out there sampling things, checking out what's going on, and decides whether something is infected."

In other words, a healthy immune system is a good communicator: It works nimbly with each of its parts to tackle what it needs to while refraining from overreacting.

Having a compromised immune system isn't the same as having a "weak" one. To be immune-compromised means that a particular part of your immune system doesn't work as well as it should, Lacy-Hulbert says.

Those who may be considered immunocompromised may include people who don't have T or B cells, which can make it very difficult for them to fight off infections. In milder forms, a compromised immune system might be one that doesn't function properly — maybe the B cells are produced, but the antibodies they produce aren't great at making memories.

Sometimes, it's the luck of the draw. Genetics play a big role in determining our immune strengths, weaknesses and overall abilities.

"There's a tremendous amount of genetic variability in terms of immune function and the capacity to detoxify or to transform certain foods or pollutants or infections," Dr. Li says. "But what we're finding right now is that a huge amount of the variability depends on the total lifestyle — not just what we're eating, doing, drinking, breathing, but also what we're thinking and feeling."

Our emotions and thoughts have potential to majorly influence the immune system, Dr. Li says.

For this reason, she says relieving stress can positively affect the immune system. Practices like yoga, meditation and qigong can help put you in the "rest and restore state," she says, which, in turn, could help the immune system rest and restore, too.

While research around how emotions affect our immune systems is pretty nascent, Lacy-Hulbert says that "it's becoming more obvious that there is quite a specific link between the nervous system and the immune system."

Indeed, a March 2017 review in Dialogues in Clinical Neuroscience concluded that the emotional and immunological systems "talk" to one another, and that more research needs to be done in this area.

Still, Lacy-Hulbert says, there are "many things about the immune system and function of the body as a whole that we still don't really understand."