In the great game of disease prevention, you can always count on strong opponents:
brutal bacteria, vicious viruses and cunning cancer cells. But the home team's
no slouch, either. Meet the stellar players who provide
championship-caliber health defense.
Antibodies, interleukins, T cells… sometimes trying to decipher the intricacies of the immune system is like attempting to figure out who all those guys around the batting cage are without having a scorecard handy. “There’s a lot of redundancies in the immune system,” says Dr. Zuhair Ballas, Director of the Division of Allergy and Immunology at the University of Iowa Hospitals and Clinics. “Not only is it intricate but all of the mechanisms are interconnected.”
Fortunately for you, the home team is always battling hard whether you pay attention to the game or not. But wouldn’t you like to know who’s on your side and what positions they play?
A big reason to care about who is taking the field: Immunity is under attack from all sides nowadays.
HIV provides the most famous—and infamous—example of an agent that impairs immune response, but evidence suggests that stress, poor diet and lack of exercise (or, conversely, exercising to excess) can also hinder the immune system. And even as some factors depress immunity others cause it to go into hyperdrive, resulting in autoimmune disorders.
While various immune cells (known collectively as white blood cells) and chemicals can be found throughout the body, their main mode of transportation is a thick liquid called lymph that, like blood, circulates through its own collection of vessels. Lymph collects in specialized centers called lymph nodes (the “swollen glands” associated with a sore throat are actually lymph nodes located in the neck; other sites rich in lymph nodes include the armpit and groin). Lymphatic tissue is also found in the small intestine, spleen and tonsils.
Basic to knowing when the body is being threatened is an ability to tell “self”—the body’s own cells—from “non-self”—infectious microbes and other hazards. That’s the job of the major histocompatibility complex (MHC), which consists of molecules on each cell’s surface that identify it as belonging to the body. Every person’s MHC is unique.
Cells at Bat
Like a lineup stocked with different kinds of players, from home run thumpers to speedy singles slappers, the immune system fields an impressive array of cellular hitters.
The big boppers of the white cell world are the macrophages (which translates literally to “big eaters”) and the neutrophils, both of which are large cells that gobble up stuff like toxins, some microbes and cancer cells (known collectively as antigens, or substances that can provoke an immune response). The difference lies in where they reside. Macrophages stay in places where organs connect with the bloodstream or with the outside world (like the lungs); neutrophils circulate in the blood, ready to leap into action at a moment’s notice. Often, the two types of cells work as a team, with macrophages calling in neutrophil backup when needed.
Lymphocytes, smaller than macrophages and neutrophils, come in three main types: natural killer (NK) cells, B cells and T cells. NK cells are tiny predators, laying waste to certain microbes and some cancer cells. B cells secrete proteins called antibodies (discussed in the next section). Baby T cells go to school in the thymus, a gland at the base of the neck, where they learn how to tell self from non-self. Once they grow up, they move into the bloodstream where their higher education—becoming sensitized to a specific immune-stirring substance—continues.
No baseball team goes very far in the playoffs without a strong bullpen, pitchers who can come in when the game’s on the line and shut down an opponent’s offense. In the same way, the immune system’s cellular lineup is complemented by a powerful collection of chemical hurlers.
B cells produce antibodies, also known as immunoglobulins (Ig). There are several varieties of Ig, among them IgA, which helps the body fight microbes that break through surfaces lined by mucous membrane, such as the respiratory and digestive tracts, and IgE, the type implicated in allergic reactions.
Two other antibodies are responsible for responding to microbial threats. IgM is the first antibody responder; it is the antibody that is produced on first exposure to a new antigen. For example, when a child gets his or her first tetanus shot the first antibody that is made is IgM. Soon afterward (10 to 14 days), another antibody, IgG, is produced. Upon re-exposure, for example getting a tetanus booster shot, the immune system does what is called a “secondary” response which is “faster, higher, stronger”: It can be detected as early as three days later; the amount of the antibody is higher and, although some IgM is made, most of the antibody is IgG. In general IgM patrols the blood while IgG patrols the tissues. Antibodies are important in fighting bacteria but T lymphocytes are more important in fighting viruses.
Cytokines, the second major group of chemicals, are the immune system’s ever-helpful crew of messengers, assistants and regulators, ready to enable some aspects of the immune response while inhibiting others. Cytokines include more than 30 interleukins, which perform a wide variety of tasks, among them getting immune cells to proliferate and become active; interferons, which hamper virus replication and tumor growth; and tumor necrosis factors, which, as their name implies, go after cancer cells.
Taking the Field
The immune system fields a pretty impressive squad, doesn’t it? Now it’s time to see them in action.
First up is the innate immune system, the kind that’s at the ready from the moment you’re born. It consists of “neutrophils, macrophages and NK cells along with the complement system, a cascade of proteins necessary for the optimal function of the immune system against bacterial infection,” says Ballas. “Your innate immune system is the same as that of the person next to you.”
If the innate immune system is like a muscular but not too bright slugger, the adaptive (or specific) immune system is like a skinny but smart and crafty pitcher. “The adaptive immune system has a blueprint of everything you’ve been exposed to ever since you were born,” says Ballas. “It learns, it adapts and it remembers.” Both B and T cells are involved in adaptive immunity. “T cells can live for decades,” Ballas notes. “There are two major kinds of T cells: T-helper cells, which help the B cells make antibody, and T-killer cells, which kill cells that have been infected with viruses or fungi.”
The ability of adaptive immunity to keep track of the antigens it runs across helps explain why children get so many more upper respiratory infections than adults; a child’s adaptive immunity is still learning—the hard way—how to deal with all the different types of sniffle-causing agents that exist, while an adult’s immune system has already learned to defend against most of those agents.
This also explains why everyone’s adaptive immune system is different, since no two individuals are exposed to the exact same set of microbes over the course of a lifetime.
When activated, immune response often causes the swelling, pain and redness of inflammation, which can turn hazardous if it becomes chronic.
Staying in the Game
When the immune team is playing well you reel off win after win over threats to your health. But sometimes the team doesn’t play so well, and that’s when trouble begins.
Sometimes the immune system goes haywire and attacks the body’s own tissues, like a slugger who strikes out and beats up the bat rack in frustration. “Over the past couple of decades,” notes Ballas, “we have had an explosion of increased incidence in immune imbalance leading to marked increases in allergies and asthma and in autoimmune diseases.”
What triggers autoimmunity? One theory in current favor is the hygiene hypothesis, which grew out of the observation that some autoimmune diseases are much more prevalent in developed countries, where things tend to be really clean. “In the developing world, people grow up in a non-sterile environment—being exposed to farm animals and such—and that would boost the regulatory arm of the immune system,” Ballas explains. “When the environment is overly sterile, the immune system doesn’t learn how to separate the wheat from the chaff. So when the immune system sees ragweed it starts pumping out molecules that give you allergies.” That’s why children who go to daycare have more infections but fewer allergies—their immune systems get a jump on spring training.
On the other hand, an immunity team depleted by injuries has a hard time winning games. “People who are stressed are more likely to catch infections,” says Ballas. “Researchers are just starting now to do the right studies.” Poor diet and a toxic environment are other factors: “We start doing a lot of bad things to our immune system: being overweight, eating junk food. There is a lot of pollution in the atmosphere that may produce free radicals, which may harm the immune system.”
How can you help your team train for peak performance? “Fresh fruit and exercise tend to improve your immune system,” Ballas says (although overly intense training can actually deplete immunity). “And there’s no question that antioxidants are important for a healthy immune system.” Finding some way to unwind—from meditation to martial arts—is a good idea, as is attending to such basics as getting enough sleep and washing your hands often.
So prepare your immunity all-stars for the grueling season ahead. Putting in time on the practice field will lead to a disease-prevention championship later!
Energy Times wishes to thank Dr. Ballas, who kindly agreed to review the main text of this article for technical accuracy.