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Acquired Immunity Definition

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Medical provider holding a syringe and a vial of vaccine

You may not realize it, but every day you are exposed to countless pathogens that could make you sick.

Fortunately, your body has a powerful defense system that can recognize and eliminate these invaders before they cause harm.

This system is called acquired immunity, and it’s the key to staying healthy in an increasingly dangerous world.

What is Acquired Immunity?

Acquired immunity is a complex process that involves many different components working together to protect your body from infection.

When your body encounters a new pathogen, such as a virus or bacteria, it develops specific antibodies that can recognize and neutralize that pathogen.

These antibodies are produced by specialized cells in your blood called white blood cells, which learn how to recognize and respond to the pathogen more quickly each time they encounter it.

Types of Acquired Immunity

There are two types of acquired immunity: active and passive.

Active immunity is generated when your body encounters a pathogen for the first time and develops its own antibodies to fight it off.

This process takes time, but it results in long-lasting immunity that can protect you from future infections.

Passive immunity, on the other hand, is when you receive pre-made antibodies from another source, such as through breast milk or a vaccination.

This type of immunity provides immediate protection but is usually short-lived.

Acquired immunity is an essential aspect of your overall health and well-being.

Without it, you would be vulnerable to a wide range of infectious diseases and illnesses.

By understanding how acquired immunity works and taking steps to strengthen it, you can protect yourself from these threats and live a healthier, more fulfilling life.

Ways to Strengthen Acquired Immunity

To strengthen your acquired immunity, there are several things you can do.

Getting vaccinated against common diseases can help your body build up immunity to those pathogens.

Eating a healthy diet, getting regular exercise, and getting enough sleep can also help support your immune system and keep you healthy.

Acquired Immunization (Adaptive Immunity)

a baby had immunization inside a clinic

Acquired immunity, also known as adaptive immunity, is a powerful defense mechanism that helps protect our bodies from harmful substances.

This process tailors its attack to each specific antigen it encounters, making it highly effective in fighting off disease-causing pathogens.

To understand how acquired immunity works, we can look at two types of immunizations: active and passive.

Active immunization happens when our own immune system creates antibodies after encountering an antigen directly.

This stimulates the adaptive immune response.

Passive immunization involves introducing preformed antibodies from another source into our bloodstream.

Both processes are used to prevent certain diseases, but active immunization provides more effective and longer-lasting protection.

Acquired immunity works by recognizing foreign substances in our body, initiating an immune response, and producing memory cells that remember the encountered antigens.

This way, if similar antigens are experienced again, our bodies can respond more quickly and efficiently than before.

B Cells and T Cells

Active acquired immunity is the body’s complex defense system that involves B cells and T cells.

The first step involves the introduction of antigens into the body, which are then recognized by specialized receptors on B cells or T cell surfaces called antibodies.

Memory B and T cells are produced to remember these antigens for future encounters.

This active form of acquired immunity provides us with much greater protection than passive immunity alone.

By remembering encountered antigens and being ready to respond quickly, our bodies can protect us from potentially harmful substances without having to learn each time they enter our systems anew.

B cells are like tiny soldiers that produce special proteins called antibodies to fight off specific invaders like bacteria or viruses.

When a B cell encounters a pathogen, it creates antibodies that are tailor-made to destroy that particular invader.

T cells, on the other hand, are responsible for recognizing these pathogens in our bodies and starting the destruction process.

They can kill infected cells directly, release chemicals called cytokines to alert other parts of the immune system, or activate B cells to produce even more antibodies.

To work properly, B and T cells need to have recognition sites on their surface to detect antigen molecules on pathogens.

This allows our acquired immunity to respond quickly and effectively to potential infections or illnesses, which helps keep us healthy.

B cells and humoral immunity

B cells are an important part of acquired immunity and they play a big role in humoral immunity.

This type of immunity involves three steps: first, B cells have to find the antigen; then, they produce antibodies; and finally, those antibodies either weaken or eliminate the invader.

During this process, the antibodies interact with antigens on the surface of microbes like viruses and bacteria.

This interaction triggers a whole series of events that can lead to the pathogen being destroyed directly or by other immune cells like macrophages or complement proteins.

With B and T cells working together, we’re able to fight off all sorts of nasty invaders and stay healthy.

Challenges Of Active Acquired Immunity

Active acquired immunity has some challenges to overcome. The slow onset of protection after exposure leaves us vulnerable to infection for several days. The use of antigens and foreign proteins can trigger adverse reactions. Boosters may also be needed to maintain immunity over the long haul.

The development of active acquired immunity involves the interaction of different cells, B and T lymphocytes, and antigen presenting cells (APCs). It takes time to produce specific antibodies against the pathogen’s antigens.

The challenges of active acquired immunity include:

  • Delayed onset – Protection takes several days to develop following exposure.
  • Risk of adverse reactions – Vaccines can trigger mild side effects.
  • Need for booster doses – Boosters are necessary to maintain immunity over time.
  • Limited effectiveness – It only protects against specific infections and not all illnesses, including new strains or variants.

Passive Acquired Immunity

Passive acquired immunity is a type of protection against infectious agents that involves transferring ready-made antibodies from another source, rather than relying on the body to produce its own. 

This pre-established protection can be useful in situations where speed and efficiency are important, such as in newborn babies who lack their own immune system at birth.

Passive acquired immunity can be achieved through natural or artificial means. Natural passive acquired immunity occurs when a baby receives antibodies from their mother during pregnancy or breastfeeding. 

Artificial passive acquired immunity occurs when someone receives antibodies either as injections or orally. These external sources provide short-term immunity until the person’s own immune system takes over and produces specific antibodies for longer-term defense.

Passive immunization has been widely used to combat infectious diseases such as rabies and measles, among many others. However, it’s important to note that regular maintenance is needed to ensure optimal protection throughout treatment cycles.

How Passive Acquired Immunity Can Be Natural

Passive acquired immunity is a powerful tool for protecting individuals against infectious diseases.

Whether obtained naturally from mothers during pregnancy and breastfeeding or through artificial means like injections or oral medications, this form of immunity offers several key advantages.

Passive acquired immunity provides immediate protection against pathogens and other foreign substances, even before an individual’s own immune system has a chance to produce its own antibodies.

This rapid response can be especially important for individuals who have been exposed to particularly virulent or fast-spreading diseases.

Passive acquired immunity can help prevent further development of an infection once someone has already been exposed to it.

By neutralizing the pathogen before it can spread too far, passive acquired immunity allows the person’s body to focus its energy on fighting existing infections, rather than having to divert resources towards developing new ones from scratch.

This can speed up the recovery process and reduce the risk of complications.

Passive immunity can also help protect public health by reducing the spread of infectious diseases.

Since individuals who have received passive immunity are less likely to become infected, they are also less likely to infect others around them through contact or airborne transmission.

This can be especially important for controlling outbreaks of highly infectious diseases like measles or influenza.

Passive Acquired Immunity: Advantages and Limitations

Passive acquired immunity provides natural or artificial protection against infectious diseases, offering immediate protection and preventing the progression of illness. 

This defense has advantages, especially for those exposed to viruses and bacteria. Dendritic cells, specialized immune cells, play a vital role in passive acquired immunity by detecting pathogens and initiating an appropriate response, protecting the body from infection.

Aside from rapid protection, passive acquired immunity helps prevent further infection, allowing the body to focus on fighting existing infections. This also reduces the risk of infecting others through contact or airborne transmission, making it a valuable tool for protecting public health.

However, passive acquired immunity has limitations. Its short-lived duration and inability to form memory cells may not protect against multiple encounters with a pathogen or infection. 

There is also a risk of allergic reactions associated with this type of immunity, especially if the recipient’s white blood cells contain cytotoxic T-cells that react negatively to certain antigens.

While passive acquired immunity provides immediate protection, relying on active forms of immunization through vaccines often provides better long-term outcomes for protecting your health. 

Active acquired immunity stimulates the body’s immune system by introducing small amounts of antigen, creating memory B- and T-cells that remember how to fight off future invasions more quickly and efficiently. Allergies are also less common when active acquired immunity is employed as part of a vaccine regimen.

Components Of Acquired Immunity

Acquired immunity is a type of immunity developed by the body after exposure to an antigen.

The components of acquired immunity are essential for protection from pathogenic organisms and foreign antigens.

There are two main types of acquired immunity: humoral-mediated and cell-mediated.

Humoral-mediated immunity involves the production of antibodies in response to foreign antigens which can be either natural or artificial, depending on if they have been produced by the body itself or injected into it.

This type of immune response is mediated by B lymphocytes that produce immunoglobulins, also known as effector cells.

These antibodies work to recognize and bind with antigens and then neutralize them so that they cannot infect other cells.

Cell-mediated Immunity relies on T cells instead of B lymphocytes to mediate its responses against specific pathogens or antigens.

In this case, T cells interact directly with foreign material such as bacteria, viruses, fungi, protozoa and parasites in order to destroy them before they cause harm inside the body..

Here are some key components associated with cell-mediated immunity:

  • Recognition – T Cells must identify the presence of a foreign antigen in order to respond appropriately;
  • Activation – Once identified, T Cells are activated by cytokines released from macrophages;
  • Differentiation – Differentiated T Cells will release different types of molecules based upon their function (e.g., interferons);
  • Effector Mechanisms -T Cell activation leads to various effector functions including direct lysis of target cells and indirect regulation via secretion of cytokines;
  • Memory Formation – Long term memory formation occurs when these same processes repeat over time allowing for improved recognition and faster response times during future exposures.

The ability for our bodies to mount an effective defense against harmful agents depends heavily upon both humoral-mediated and cell-mediated forms of acquired immunity working together simultaneously.

While each has its own strengths and weaknesses, combined they create a formidable barrier between us and potential disease causing organisms within our environment.


Q: What is the difference between innate and acquired immunity?

A: Innate immunity is your body’s first line of defense against infections.

It consists of physical barriers (such as skin and mucous membranes), chemical substances (such as enzymes and acids), and cells (such as natural killer cells and phagocytes) that can recognize and destroy common pathogens without prior exposure.

Acquired immunity is your body’s second line of defense that involves specialized cells (such as T cells and B cells) and molecules (such as antibodies and cytokines) that can recognize and eliminate specific pathogens after previous exposure.

Q: What are lymph nodes and why are they important for acquired immunity?

A: Lymph nodes are small organs that filter lymph, a fluid that carries white blood cells, antigens, and waste products.

Lymph nodes contain clusters of immune cells that can activate acquired immune responses when they encounter foreign antigens.

Lymph nodes also serve as sites where immune cells can communicate with each other and coordinate their actions.

Q: How does acquired immunity help with disease control?

A: Acquired immunity helps with disease control by preventing reinfection by the same pathogen or reducing its severity.

When your body encounters a pathogen for the first time, it takes time to mount an effective acquired immune response.

This is called the primary response.

However, if you encounter the same pathogen again, your body can quickly recall its memory of that antigen and produce a stronger and faster response.

This is called the secondary response or immunological memory.

Immunological memory can protect you from diseases such as measles, chickenpox, tetanus, etc.

Q: How does acquired immunity fight cancer cells?

A: Acquired immunity fights cancer cells by recognizing them as abnormal or foreign and eliminating them before they grow out of control.

Cancer cells are cells that have mutated or been damaged by factors such as radiation, chemicals, viruses, etc.

Some cancer cells can evade detection by the innate immune system by hiding their antigens or producing immunosuppressive molecules.

However, an acquired immune system can detect subtle changes in antigens on cancer cells using specialized receptors on T cells called T cell receptors (TCRs)³. TCRs bind to antigens presented by antigen presenting cells (APCs), such as dendritic cells or macrophages

Once activated by APCs, T cells can kill cancer cells directly or recruit other immune cells to help.

Q: What are some examples of lymphoid organs involved in acquired immunity?

A: Lymphoid organs are organs where lymphocytes (a type of white blood cell) develop, mature, or reside.

They include primary lymphoid organs such as bone marrow (where all blood cells originate) and thymus (where T cells mature), secondary lymphoid organs such as spleen (where blood-borne antigens are filtered), lymph nodes (where lymph-borne antigens are filtered), tonsils (where oral-nasal antigens are filtered), appendix (where intestinal antigens are filtered), Peyer’s patches (where intestinal antigens are sampled), etc., tertiary lymphoid organs such as mucosa-associated lymphoid tissue (MALT) where mucosal surfaces are protected.

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