What is Immune Memory – How Does It Work By Dr. Sagar Bhattad

The immune system can be classified into

1. Innate Immunity

The immunity, we are born with – our bodies’ first barriers (skin, mucous membrane, tears, gastric juice, etc.)

2. Adaptive Immunity

What does your immune system develop along the way? The body develops antibodies to fight the pathogens that invade our bodies. Since it can remember the foreign invaders and enemies from previous encounters, this arm of the immune system has the immune memory

3. Passive Immunity

What a baby derives from its mother, which does not last beyond the first few months of their lives.

How Do Immune Memory Cells Prevent Illness?

The immune system is made up of T-cells and B-cells, which are responsible for both recognizing pathogens and remembering the antigens. While the T-cells recognize and eliminate the foreign invaders or pathogens, the B-cells produce antibodies to fight the pathogens.

When a pathogen enters the body, the immune system recognizes it and starts attacking it. Such attacks can vary in time depending on the type and extent of the infections. When the body recovers from the infection, the immune system has learned to successfully defeat the pathogen. It now has developed cells called memory cells, which remember the pathogen.

Every time a pathogen enters your child’s body, it triggers an immune response. If the pathogen is not new, the memory cells will recognize it and the B-cells will produce the antibodies. The immune system can eliminate the infection without much of a fight. It remembers how it fought it the last time.

If it is a new infection, the T-cells and B-cells need to understand how to fight it and produce antibodies accordingly. This can take time. At such times, the child can have a mild to high fever, that can last longer than usual.

Why Do Children Develop So Many Viral Fevers?

At birth, the immune system is immature and there is no memory for any pathogens. A baby derives a little immunity from the mother, which slowly fades out by the time they are 3 months old. The vaccinations and repetitive exposure to infections and pathogens in the atmosphere are what stimulate the immune system to start working and fighting. Over time the immune system develops a memory, which helps it keep us strong and fight infections more effectively.

When your child has an infection, their immune system will respond to the attack and start fighting back. During this time the body temperature will go up, resulting in a fever. The fever can be mild or high depending on the level of infection and the fight going on inside the body.

When the body’s temperature is high, causing a high fever, it can increase the speed at which the cells work against the infection. The higher temperature can also make it an unfavorable place for the virus or bacteria to thrive, thus reducing their effect or killing them.

Sometimes, one may require external reinforcement like medications to help the immune system fight better. In the case of children, their immune system is still immature. They still do not have much exposure to many pathogens in the environment, and as a result of which the immune system does not know how to fight them.

If your child develops a viral fever, it indicates the immune system has identified a foreign invader and is fighting it. If the fever is very high or persists for days, it could mean the body is still fighting and needs more support. This is when doctors might usually prescribe medications to fend off the infection. If the pathogen is recognized, an appropriate medicine like antibiotics will be prescribed to help the immune system fight back.

The Role of Immune Cells in Immune Memory

The immune system comprises many components. In addition to the white blood cells, it consists of the spleen, bone marrow, lymphatic system, thymus, tonsils, adenoids, and appendix.

The immune system’s memory is a part of acquired immunity. With repetitive exposures to infections and vaccinations, the body acquires immunity, which is then stored in the immune memory. The immune memory mainly comprises T-cells and B-cells.

1. T-Cells

T-cells are an integral part of the immune system. They develop from the stem cells that are present in the bone marrow. Also known as T lymphocytes, the T-cells help fight new pathogens.

These cells release from the thymus into the bloodstream as naive T-cells, meaning, they have not yet seen any pathogen. They look around for an antigen-presenting cell (APC). Once they find a recognizable APC, they will receive signals to mature into effector cells.

Effector T-Cells

The effector T-Cells are of three types:

1. Cytotoxic T-Cells

This type kills the toxic cells, causing the infection, through the apoptosis process. In this process, the infectious cell is destroyed from the inside.

2. Helper T-Cells

These cells are responsible for the adaptive immune response and are very important to the immune system as a whole. These cells activate once the B-Cells provide the antigens and also have the ability to differentiate into cell subtypes. So, once the antigen is ready, the helper cells get activated and multiply. It then secretes cytokines, which bring the cytotoxic T-cells and macrophages to the site of infection. Together, the infectious cells are destroyed and the infection is healed.

3. Regulatory T-Cells

Once the infection is destroyed, these regulatory T-cells will help stop the immune response. It is the duty of these cells to ensure the other T-Cells (cytotoxic and helper T-Cells) do not continue attacking or accidentally attack healthy cells, by removing them completely.

Memory T-Cells

After the infection is identified, recognized, and fought with, most of the effector cells are removed from the site. However, some T-cells still remain. These are long-living cells, which are also memory cells. So, the next time the same infection or pathogen enters the body, these memory cells will remember the antigen/pathogen and signal the immune system to attack the pathogen immediately. It saves a lot of response time and helps the body heal faster.

So, to sum up, the work of the T-cells: the naïve T-cells will recognize and adapt to the infection-causing pathogens, the effector cells will help destroy and fight them and the memory cell will help remember this response for future defense.

2. B-Cells

When a pathogen enters the body, the immune system activates the B-cells. These cells immediately divide and differentiate into essential plasma cells. The plasma cells then make the antibodies required to fight the pathogens.

While some of these proteins (antibodies) identify intruders that need to be destroyed, some of these antibodies will bind themselves to the pathogen. When the antibodies bind to the pathogens, it makes the pathogen ineffective and neutralizes it. As a result, these pathogens cannot infect any cells anymore. So, the B-cells neutralize the infection to prevent an attack.

The B-cells have a short lifespan and will die soon after they fight the infection. Some B-cells last long. These are made in the germinal centers in the lymph nodes. Only the best B-cells that can produce the antibodies that can bind well, will go on to become a part of the immune memory.

When an infection occurs, these memory B-cells will quickly divide into plasma cells which make the antibodies. Hence the strong B-cells not only help by binding to the pathogen. But will also help in the future by adding to the immune memory.

The T-cells and B-cells work in tandem to help develop the immune memory and improve the immune system as a whole. If these cells don’t work properly, it can result in immune system disorders like immunodeficiencies, autoimmunity, or hypersensitivity.

[Read : Primary Immunodeficiency in Children]

How Does Immune Memory Work?

The immune memory works just like our memory. It recognizes pathogens, remembers the impact and the fight against them, recollects the antigen, and uses the information to fight again.

The T-cells and B-cells work together to eliminate the infection from the body. Next time when the same virus or pathogen enters the body, the immune memory will work in the following way:

• Step 1: The T-cells will recognize the pathogens from the previous time
• Step 2: The T-cells will trigger the B-cells to start producing the appropriate antibodies
• Step 3: The T-cells will use the antibodies to fight and remove the infection from the body.

Now, the time taken for the B-cells to produce the antibodies and for the T-Cells to effectively use them in removing the infection will vary from one infection to another, one time to another.

Once these cells remove the infection successfully, the body is healed and healthy once again. This process keeps repeating with every pathogen that enters the body and the memory keeps building up. This is why an adult has better immunity than a child. The more exposures, the better the immune memory and the quicker the immune response.
The memory cells – in both the T-cells and the B-cells are long-lasting unlike the other types of these cells which die as soon as the infection is removed.

How Long Does Immune Memory Last?

Immune memory can last a very long time. Sometimes, it can last as long as 75 years. This is why some people are able to recover well from infections, despite their age. Some people will develop lifelong immunity from certain illnesses while immunity to other infections can decrease with age.

The immune memory can also reduce or fade away, leading to more infections or illnesses as a person gets older. In some cases, like smallpox, chicken pox, measles, or polio, the immune memory can last longer. The response derived from vaccinations or previous exposure can protect the person from those particular illnesses, as long as they live.

How Does Immune Memory Help Children?

Children encounter numerous infections as they grow up. School-going children are more prone to recurrent infections and fevers as the exposure level is high when compared to a smaller child who is yet to start school.

Every time your child encounters a pathogen in their environment, their immune memory will recognize and fight the infection to keep your child safe. This is an ongoing process until a new pathogen enters the body. When their immune system encounters a new pathogen, it learns to fight it by developing appropriate antibodies.

Now, as the child grows up, their immune system will too. The immune memory keeps growing with every infection or disease. This memory helps in healing your child faster to keep them safe and strong. Over time, your child’s body will learn to function as normally as possible, despite an infection, thus helping them lead regular lives without much disturbance.

[Read : Recurrent Infections in My Toddler]

Your Child’s Immune Memory In A Nutshell

Let’s try to understand this better with an example –

When your child is very young and just starts school, they might fall sick very often, requiring you to take off from school regularly. As they grow, such events will reduce and your child may not fall sick so often. After a few more years, they will be healthy enough to go to their school or continue with their daily activities despite a cold, cough, or some mild infection.

This is because their immune memory is building with every exposure and the body is learning to fight the pathogens more effectively. So, when we say the child will get stronger as they grow older, it is not just their physical size or age but also their immune system.

Now, in the case of a child with some immune deficiency or insufficient exposure to the outside world due to home-schooling, the situation can be different. Despite being older and bigger, they may still be prone to many infections when they join regular school or step out regularly.

Despite their age, the child’s immune system is still immature and has not had many encounters with pathogens to build a good memory. So, they can fall sick often and take more time than kids their age, to recover from an illness.

Conclusion

Immune memory helps the immune system get stronger and more effective in its fight against foreign invaders. The better the immune memory, the more effective will the immune system be. The immune memory grows as a person grows, and this is why many adults have better immunity than children.

FAQ’s

1. Do You Inherit Immune Memory?

The immune memory mainly comes from acquired immunity, which comes from an individual’s exposure to pathogens and vaccinations. The immune memory depends on the pathogens that enter the body and how the body responds. So, one cannot inherit the immune memory from their mother or father.

2. Where Are Memory Cells Located?

Memory cells are located in the bone marrow. This is where both the T-cells and the B-cells are generated and trained to effectively attack the infections. Sometimes, these memory cells are present in the organs too.

3. Can Immune Memory Prevent A Disease From Attacking You Twice?

It depends on the type of antibodies the body generates for the infection. In some cases, the body produces lifelong immunity, where it can prevent the same infection from attacking you twice. In some cases, the body will respond by producing relevant antibodies after the attack and help you heal faster. In case of severe infections, though the body has fought it before and has a memory of the antigens, it needs external reinforcements to fight effectively.

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