Last Updated on July 17, 2023

Acquired immunity is a sophisticated defense system that provides specific and durable protection against a wide array of pathogens. It develops through exposure to pathogens or vaccination, enabling the immune system to mount targeted responses and establish immunological memory.

In this article, we will explore the fundamental principles of the acquired immune system, examining its definition, integral components, and the intricate mechanisms by which it defends our health.

What Is Acquired Immunity?

Acquired immunity, also known as adaptive immunity or specific immunity, refers to the immune defense that an individual builds up over their lifetime in response to exposure to various pathogens.

This type of immunity is characterized by its specificity for particular pathogens and its ability to remember past infections during the primary immune response. This leads to a faster and stronger secondary immune response if the same pathogen is encountered again, which is termed immunological memory.

Acquired Immunity vs. Innate Immunity

Innate immunity, as the first line of defense, is a broad, non-specific immune response that is present from birth and works to quickly combat pathogens without needing prior exposure. It includes physical barriers like skin and mucous membranes, and immune cells like neutrophils and natural killer cells, which respond in the same way to all pathogens they encounter.

Acquired immunity, as mentioned earlier, is a tailored, pathogen-specific response developed over a person’s lifetime as the immune system encounters and learns from different pathogens.

Types of Acquired Immunity

In the acquired immune system, there are two primary types of immunity: active and passive.

Active Acquired Immunity

Active acquired immunity refers to the defense mechanisms developed by an individual’s immune system in response to direct exposure to a pathogen or its antigens, either through prior infection (natural immunity) or vaccination.

This process involves the production of antibodies by B cells and the activation of T cells, which can remember and rapidly respond to future encounters with the same pathogen. Active immunity takes time to develop but provides long-lasting protection.

Passive Acquired Immunity

Passive acquired immunity, in contrast, is a temporary form of immunity that results from the transfer of antibodies or immune cells from an immune individual to a non-immune individual. This can occur naturally, such as the transfer of antibodies from mother to child during pregnancy and breastfeeding, or can be induced medically, such as through the administration of immune serum or monoclonal antibodies.

While passive immunity provides immediate protection, it does not involve the recipient’s own immune system in producing a response, and therefore, the protection it provides wanes over time.

Branches of the Acquired Immune System

There are also two distinct branches of the acquired immune system: cell-mediated immunity and humoral immunity.

Cell-Mediated Immunity

Cell-mediated immunity is primarily driven by T cells, which become activated when they encounter antigens presented by other cells in the body. These activated T cells then either directly destroy infected cells (as is the case with cytotoxic T cells), or they release cytokines that stimulate other immune responses (as with helper T cells).

Importantly, cell-mediated immunity is especially effective against cells infected with viruses, some bacteria, and cancer cells, which can hide from other parts of the immune system.

Humoral Immunity

Humoral immunity involves the production of antibodies by B cells in response to exposure to specific antigens. These antibodies circulate in bodily fluids, or ‘humors,’ and can neutralize pathogens, prevent them from entering cells, and target them for destruction by other immune cells.

Unlike cell-mediated immunity, humoral immunity is particularly effective against pathogens outside of cells, such as bacteria and viruses in their free form, and toxins.

Components of the Acquired Immune System

The acquired immune system contains three primary components: B lymphocytes, T lymphocytes, and antigen-presenting cells.

B Lymphocytes (B Cells)

B lymphocytes, or B cells, are a vital component of the acquired immune response, with their main function being the production of antibodies against specific antigens. These cells undergo a maturation process, transitioning through several stages and ultimately differentiating into specific subsets, each with a unique role in the immune response.

  • Naive B Cells: These are mature B cells that have not yet encountered their specific antigen. They circulate in the blood and lymphatic system, waiting to be activated by their antigen. Once activated, they undergo clonal expansion and differentiate into plasma cells or memory B cells.
  • Transitional B Cells: These cells represent an intermediate stage between immature B cells in the bone marrow and mature naive B cells in peripheral lymphoid organs. They are crucial in the process of B cell maturation, undergoing several checks to ensure self-tolerance and prevent autoimmunity.
  • Plasma B Cells: When a naive B cell encounters its specific antigen and receives additional signals from helper T cells, it differentiates into a plasma cell. Plasma cells are the antibody factories of the immune system, producing and secreting large amounts of specific antibodies that can neutralize the pathogen carrying the recognized antigen.
  • Memory B Cells: These cells are generated during a B cell response to an antigen and provide long-term immunity. They remember the specific antigen, and upon subsequent exposure, they can rapidly differentiate into plasma cells, producing antibodies much quicker and in greater amounts than during the first exposure.

T Lymphocytes (T Cells)

T lymphocytes, or T cells, are fundamental players in the acquired immune response, possessing the ability to both orchestrate the immune response and directly kill infected cells. Each subset of T cells serves a unique role in identifying and combating pathogens, thus maintaining the body’s overall health and immunity.

  • Helper T Cells (CD4+ T cells): These cells, known as the “generals” of the immune system, play a crucial role in orchestrating the immune response. Upon encountering antigens presented by antigen-presenting cells, they release cytokines that can stimulate B cells to produce antibodies, enhance the killing efficiency of cytotoxic T cells, and promote the activities of other immune cells.
  • Cytotoxic T Cells (CD8+ T cells): These cells are the “soldiers” of the immune system, directly killing cells that are infected by viruses or transformed by cancer. They recognize infected or cancerous cells through interaction between their T cell receptors and specific antigens presented on the target cells’ surface, leading to the release of cytotoxic granules that induce cell death.
  • Regulatory T Cells (Tregs): These cells play a critical role in maintaining immune homeostasis and preventing autoimmunity by suppressing excessive immune responses. Tregs can inhibit the activation and proliferation of other T cells, as well as modulate the function of other immune cells, such as B cells and antigen-presenting cells.
  • Memory T Cells: These cells are generated after an immune response to an antigen and are responsible for the rapid and enhanced response upon subsequent exposure to the same antigen. Similar to memory B cells, memory T cells “remember” their specific antigen and can quickly expand and differentiate into effector cells during a secondary infection, leading to a quicker and more potent immune response.

Antigen-presenting Cells (APCs)

Antigen-presenting cells (APCs) perform a pivotal function in the acquired immune system, as they bridge the gap between innate and acquired immunity. They are responsible for capturing, processing, and presenting antigens to T cells, thereby initiating an immune response.

  • Dendritic Cells: Acting as the immune system’s surveillance system, dendritic cells patrol the body searching for pathogens. When they encounter an invader, they ingest and break down the pathogen into smaller fragments known as antigens. These antigens are then presented on the dendritic cell’s surface, ready to be recognized by T cells and trigger an immune response.
  • Macrophages: These cells are known as the ‘big eaters’ of the immune system due to their ability to phagocytize (ingest) and destroy pathogens. After engulfing a pathogen, macrophages process the antigens and display them on their surface to stimulate T cells. Moreover, they secrete cytokines to recruit and activate other immune cells.
  • B Cells: Apart from producing antibodies, B cells also act as APCs. When they encounter an antigen that matches their B cell receptor, they can internalize it, process it, and present the resulting peptide fragments on their surface. These displayed antigens can then be recognized by T cells, leading to the activation of B cells and subsequent antibody production.

How Does Acquired Immunity Work?

Now that we’ve discussed the various aspects of the acquired immune system, let’s zoom out and see how it works in a bit more detail.

Antigen Recognition and Specificity

The first step in the acquired immune response is the identification of foreign elements or antigens.

Antigen-presenting cells such as dendritic cells, macrophages, and B cells ingest pathogens, process them into antigens, and present these antigens on their surface. T and B lymphocytes then recognize these specific antigens and initiate a targeted immune response.

Generation of Immune Memory

After initial exposure to an antigen, the acquired immune system generates memory cells.

These specialized B and T lymphocytes remember the specific antigen and, upon subsequent encounters, they respond more swiftly and effectively. This principle underlies the effectiveness of vaccinations and provides long-term immunity against specific pathogens.

Regulation of Immune Responses

Regulation is a crucial aspect of acquired immunity to maintain balance and prevent excessive or harmful responses.

Regulatory T cells, cytokines, and other mechanisms function to modulate the immune response, inhibiting overreactions that could potentially damage healthy tissues. When the threat is neutralized, these regulatory mechanisms wind down the immune response (an anti-inflammatory effect), returning the body to its normal state.

Disorders and Deficiencies in Acquired Immunity

In the realm of the immune system, acquired immunity can encounter different types of disorders which can broadly be classified into two categories: Autoimmune Diseases and Immunodeficiency Disorders.

Autoimmune diseases occur when the immune system mistakenly attacks the body’s own cells, whereas immunodeficiency disorders occur when the immune system is not functioning properly and is unable to effectively fight off infections and diseases.

Autoimmune Diseases

  • Rheumatoid Arthritis: A disease characterized by chronic inflammation that typically affects the small joints in the hands and feet, leading to painful swelling and potential joint damage.
  • Type 1 Diabetes: This condition arises when the immune system erroneously attacks the insulin-producing cells in the pancreas, resulting in high blood sugar levels.
  • Multiple Sclerosis: In this disorder, the immune system targets the protective sheath (myelin) that covers nerve fibers in the central nervous system, causing communication problems between the brain and the rest of the body.
  • Lupus: A complex autoimmune disorder that can target any part of the body, causing widespread inflammation and tissue damage.
  • Celiac Disease: This autoimmune condition is characterized by an abnormal response to dietary gluten, which results in inflammation and damage to the lining of the small intestine.

Immunodeficiency Disorders

  • Primary Immunodeficiencies: These disorders often lead to an increased vulnerability to infections, an increased risk of autoimmune diseases, or a dysfunctional response to the invasion of pathogens. Some examples include Severe Combined Immunodeficiency (SCID), Common Variable Immunodeficiency (CVID), and Selective IgA Deficiency.
  • Acquired Immunodeficiencies: These conditions may be caused by environmental factors like exposure to infectious diseases or through medical treatments such as chemotherapy. The most recognized of these is the Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome (HIV/AIDS), where the immune system’s defense against infections is severely weakened.

How to Boost Immunity Naturally

Naturally boosting the immune system is a crucial step toward maintaining overall health and reducing inflammation in the body. It requires a multifaceted approach, targeting nutrition, lifestyle habits, hygiene practices, and the use of dietary supplements. Collectively, these items can provide natural pain relief and support immune system function.

  • Nutrition and Hydration: Consuming a diet rich in immune-boosting foods like fruits, vegetables, lean proteins, and whole grains provides the necessary nutrients to support immune function. Staying hydrated assists in maintaining the health of your body’s cells, including those of the immune system.
  • Lifestyle and Habits: Regular physical activity, adequate sleep, and stress management techniques can help reduce inflammation and boost your immune system. Avoiding smoking and excessive alcohol intake can also contribute to stronger immune function.
  • Hygiene and Prevention: Practicing good hygiene, like regular hand washing, can prevent the introduction and spread of pathogens.
  • Use Dietary Supplements: Some vitamins for immunity, like vitamins C, D, and E, and minerals like zinc, may enhance immune response.

As far as antioxidants and natural anti-inflammatory supplements are concerned, the market is flooded with them and it can be difficult to discern which ones work and which don’t. Here are three products with ample research behind them to support their use in immune system support.

Turmeric, primarily due to its active compound curcumin, is known for its potent anti-inflammatory and antioxidant properties, which can enhance the body’s immune response. Curcumin has also been shown to modulate the activation of various immune cells, fortifying the body’s innate immune system.

Apple cider vinegar is rich in acetic acid and various other beneficial compounds that have antimicrobial properties, helping to fend off harmful pathogens. It’s also known for promoting a healthy gut environment, which plays a vital role in maintaining the immune system.

Elderberry is packed with antioxidants and vitamins, particularly vitamin C, that may boost your immune system. It’s been used historically to treat infections and improve immune responses, primarily due to its antiviral properties.

Acquired Immune Response: Final Thoughts

Acquired immunity, with its intricate mechanisms and dynamic components, forms a crucial cornerstone of our immune system’s defense against pathogens. Through the coordination of B cells, T cells, antibodies, and memory cells, the acquired immune system provides specific and long-lasting protection.

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