Flu Vaccine Injection Site on Arm From -CDC -Robert Denty

As you go about your daily life, consuming food and engaging in activities, a battle is being waged inside your body. You usually don't notice it, yet foreign bacteria, viruses, and other microorganisms are constantly attempting to invade from the outside world. Fortunately, your body is equipped with a powerful defense system known as the immune system, which consists of trillions of cells and proteins located in your blood and organs. Furthermore, the immune system is constantly adapting and evolving, even before you are born.

Building Your Defenses

You’re not born with a fully equipped immune system. Fetuses can produce some immune protection. But before birth, “the vast majority of protection against infection comes from the mother,” explains Dr. Whitney Harrington, who studies immune system development at Seattle Children’s Research Institute.

The immune system produces germ-fighting molecules called antibodies, which are passed to the fetus through the placenta and to the baby after birth through breastfeeding. These antibodies attach to germs and prevent them from invading cells.

“The peak risk of severe disease from many infections is under six months of life,” says Harrington. That’s because the baby’s immune system is just starting to develop.

Mothers can pass along antibodies to their babies which help protect them for several months until the baby's own immune system begins to develop.

The immune system has numerous layers of protection. Cells of the innate immune system serve as the initial line of defense, patrolling the body for signs of cellular damage or infection and destroying any that are found.

The adaptive immune system is another major defense against infectious germs. It is triggered by signals from both the innate immune system and the germs themselves, and produces a strong response. This system has the capability to remember the germs it has previously met. It also responds in a similar way with vaccinations and is responsible for the production of antibodies.

It has been discovered that, similar to antibodies, some adaptive immune cells can move from the mother to the fetus. These cells could potentially teach the fetus's immune system about viruses and bacteria the mother has had contact with.

Harrington and her team have been trying to learn more about these cells. They want to understand when this transfer happens and to use it to maximize immune protection provided by the mother.

Through infancy and childhood, your immune system matures and continues to build its own disease-fighting cells. Exposure to germs in child-hood helps the immune system grow stronger over time, Harrington says.

Protection as You Age

By the time you have reached young adulthood, your immune system has already been exposed to many germs and is prepared to respond to a variety of infections. Vaccinations further enhance this defense system by introducing either weakened or dead germs, or parts of them, to the body's immune cells, allowing them to recognize and remember how to fight off these threats without making you ill.

It is recommended that certain vaccinations be given during pregnancy to protect the baby in the early stages of life. Furthermore, additional shots may be necessary in adulthood to maintain the immune system's memory and further protect the individual. Certain individuals may need additional vaccinations due to factors such as their occupation or health status.

As one gets older, the immune system, similar to other systems in the body, may start to weaken. This can lead to a decrease in the effectiveness of the immune cells.

“With age, immune cells lose their ability to respond rapidly and robustly to infection,” says Dr. Ronald Germain, an immune system expert at NIH.

Many infections can be more serious for older adults due to reduced functioning of other body parts such as the heart and lungs, which can accumulate wear and tear with age.

An infection can cause older adults to experience more damage than younger individuals, leading to their organs and tissues not functioning correctly. Therefore, certain vaccines are highly recommended for adults over the age of 50.

Making Better Defenses

Researchers are continually trying to find ways to strengthen immune responses and vaccines. Some microbes are able to evade the immune system by changing their structure, making it hard for previously exposed immune cells to detect them. As a result, these microbes are able to remain undetected.

Dr. Shane Crotty at the La Jolla Institute for Immunology and his team are trying to take advantage of the body’s way of keeping up with these changes. A part of the adaptive immune system known as germinal centers are being studied. Located in the lymph nodes, these areas allow immune cells to develop and create better antibodies. Germinal centers are created temporarily as a result of infection or vaccination, and not only produce antibodies to combat the current germs, but also generate antibodies to fight any possible changes the virus might undergo. Cells in the germinal centers try to predict what mutations the virus may undergo.

“Germinal centers are one of the most amazing things your immune system does,” says Crotty. Take the COVID vaccines as an example. The COVID vaccines developed against the original virus caused people to make antibodies that guarded against other variants.

“All the antibodies anybody developed against other variants from vaccination came from germinal centers,” Crotty explains.

Germinal centers can remain in the body for up to six months, and the more time they are present, the more diverse the antibodies they generate.

Crotty and his team are testing if changing the way vaccines are given can help germinal centers last longer. Their recent study tested an experimental HIV vaccine in animals. Researchers gave the vaccine in many small doses over time. This produced antibodies that were more varied and lasted longer than those from the single large vaccine dose.

In the search for new methods of protecting oneself from illness, the most effective strategies are to keep up to date with one's vaccines and lead a healthy lifestyle.

Help with editing by OpenAI. Based on an article at NIH.