Last Updated on April 17, 2024

The immune system tirelessly defends our bodies against harmful invaders, such as bacteria, viruses, and parasites. But what is the immune system, and how does it work?

In this article, we will explore the immune system, unraveling how it works, discussing its vital functions, and delving into various parts, organs, cells, and immune-related diseases.

What Is the Immune System?

The immune system is a complex and intricate network of cells, tissues, and organs in the body that serves as a defense mechanism against infections and diseases.

Its function ranges from preventing entry of pathogens to detecting and eliminating those that manage to infiltrate, and remembering the ones it has previously defeated to provide lifelong protection against recurring infections.

The immune system operates on two levels: innate immunity and adaptive immunity.

Innate Immunity

Innate immunity, also known as non-specific immunity, is the body’s first line of defense against pathogens like bacteria, viruses, and foreign substances. It includes physical barriers like skin and mucous membranes, as well as internal defenses like inflammation, fever, and phagocytic cells that engulf and destroy invaders.

This type of immunity is called innate because it is present from birth and responds immediately to invaders but without the ability to remember or recognize specific pathogens on subsequent exposures.

Adaptive Immunity

Adaptive immunity, also known as acquired immunity or specific immunity, is the part of our immune system that learns to recognize and destroy specific pathogens after being exposed to them. It involves the action of lymphocytes, including T cells, which kill infected cells and regulate immune responses, and B cells, which produce antibodies that neutralize pathogens.

The unique aspect of adaptive immunity is its memory, as it remembers previous encounters with specific pathogens and responds more effectively and quickly upon subsequent exposures.

There are also two branches involved in the adaptive immune response, which are:

  • Humoral immunity, mediated by B cells, involves the production of antibodies that circulate in the blood and mucosal surfaces to neutralize and eliminate extracellular pathogens.
  • Cell-mediated immunity, carried out by T cells, is responsible for eliminating intracellular pathogens, such as viruses, by recognizing and killing infected host cells, as well as coordinating immune responses.

Types of Immune Responses

Now, let’s discuss the two types of immune responses: primary and secondary immune responses. Each is vital for a different reason.

Primary Immune Response

The primary immune response refers to the immune system’s initial reaction when it encounters a new, previously unmet antigen.

During this response, the immune system activates the appropriate B and T lymphocytes, which recognize the specific antigen. This process can take several days to fully engage, during which time the immune system produces memory cells to recognize the antigen more rapidly in the future, thereby forming the basis for the secondary immune response.

Secondary Immune Response

The secondary immune response is the reaction of the immune system when it re-encounters an antigen it has met before.

Thanks to the memory cells produced during the primary immune response, this reaction is faster, more potent, and lasts longer than the primary response. The secondary immune response is also the principle behind vaccinations, which introduce a harmless form of an antigen to prepare the immune system for potential future encounters with the harmful version.

Types of Immunity

There are also several different types of immunity worth discussing. These include active, passive, and herd immunity.

Active Immunity

Active immunity refers to the protective immunity developed when our immune system encounters and responds to pathogens or foreign substances, resulting in the creation of specific antibodies and memory cells. This type of immunity provides long-lasting protection as the immune system ‘remembers’ the specific pathogens, enabling a quicker response in subsequent encounters.

  • Natural active immunity is achieved when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response.
  • Artificial active immunity, on the other hand, is induced through vaccinations that contain weakened or dead forms of pathogens, thereby stimulating the immune system to produce a response without causing the actual disease.

Passive Immunity

Passive immunity is the type of immunity gained through the transfer of ready-made antibodies from one individual to another, without the recipient’s immune system actively engaging in the process. It provides immediate, but temporary, protection against certain diseases, as no memory cells are produced.

  • Natural passive immunity happens, for instance, when antibodies are passed from a mother to her baby through the placenta or breast milk, providing short-term protection to the infant.
  • Artificial passive immunity is achieved when antibodies created in another person or animal, such as those in anti-venom or immunoglobulin therapy, are introduced into an individual’s system to help fight off infections or toxins.

Herd (Community) Immunity

Herd immunity is a form of indirect protection from infectious diseases that occurs when a large percentage of a population has become immune to an infection, providing a measure of protection for individuals who are not immune. Immunity can be achieved through widespread natural immunity or vaccination.

In a population with high levels of immunity, the disease spreads slower as there are fewer susceptible individuals, offering protection to those who are vulnerable, like newborns, the elderly, or people with chronic illnesses.

Parts of the Immune System

The immune system is an intricate network that involves various parts that work together to defend the body against harmful invaders. These components, ranging from cells to organs, serve unique functions in the immune response.

  • Antibodies: These are specialized proteins produced by B cells, designed to recognize and neutralize specific antigens, contributing to the body’s defense against pathogens.
  • Bone Marrow: This soft tissue inside your bones is where all immune cells are initially created, acting as a ‘factory’ for our immune system.
  • Lymph Nodes: Small, bean-shaped structures that produce and store cells that fight infection and disease, acting as filters for harmful substances.
  • Lymph Vessels: These form a network throughout the body to transport lymph, a fluid containing infection-fighting white blood cells.
  • Mucous Membranes: Found lining various cavities in the body, these membranes produce mucus, a sticky substance that can trap pathogens and prevent their entry.
  • Skin: The body’s first line of defense, it acts as a physical barrier preventing pathogens from entering the body.
  • Spleen: This organ filters the blood, removes old cells and debris, and plays a role in producing white blood cells and antibodies.
  • Stomach and Bowel: These parts of the digestive system contain acid and bacteria to kill pathogens that enter through ingestion.
  • Thymus: An organ where T cells mature, an essential process for adaptive immunity.
  • Tonsils and Adenoids: These tissues in the upper throat trap germs when we breathe, preventing them from entering the body.
  • White Blood Cells: These cells, also known as leukocytes, circulate in the body in blood and lymph, defending the body against both infectious diseases and foreign invaders.

Cells of the Immune System

The immune system is composed of various types of cells, each with its unique role in defending the body against pathogens and foreign substances. These cells are grouped based on their functionality and their response to infection.

Lymphocytes

Lymphocytes are integral components of the adaptive immune system, playing critical roles in immune memory and recognition of specific pathogens. Their primary function is to respond to pathogens the body has previously encountered, ensuring a swift response upon subsequent exposure.

  • B cells (Plasma B cells, Memory B cells)
  • T cells (Helper T cells, Cytotoxic T cells, Regulatory T cells, Memory T cells)
  • Natural Killer cells (NK cells)

Phagocytes

Phagocytes act as the body’s frontline defense, with their main function being to engulf and destroy pathogens. They serve as a physical and cellular barrier against infections, eliminating foreign substances.

  • Neutrophils
  • Monocytes
  • Macrophages
  • Mast cells

Antigen-Presenting Cells (APCs)

Antigen-Presenting Cells (APCs) are instrumental in initiating immune responses by processing and presenting antigens to T cells. Their role is crucial in the bridge between innate and adaptive immune responses.

  • Dendritic cells
  • Macrophages
  • B cells

Granulocytes

Granulocytes are part of the innate immune system, named for their granular appearance, and are often the initial responders during an infection. These cells quickly react to invading pathogens, releasing their granules to kill the foreign elements.

  • Neutrophils
  • Eosinophils
  • Basophils

Immune System Disorders and Diseases

The human immune system, while incredibly proficient at safeguarding us from a multitude of external threats, is not without its share of vulnerabilities. Immune system disorders and diseases arise when this intricate defense system is compromised, either underperforming or overreacting to the stimuli it encounters.

Autoimmune Disorders

These occur when the immune system erroneously identifies the body’s own tissues as foreign threats, launching an attack against them. This misdirected immune response can lead to chronic inflammation and damage to various body tissues. Some examples of autoimmune diseases include:

  • Rheumatoid Arthritis
  • Psoriasis
  • Hashimoto’s Thyroiditis
  • Graves’ Disease
  • Type 1 Diabetes
  • Multiple Sclerosis
  • Inflammatory Bowel Disease (Ulcerative Colitis and Crohn’s Disease)
  • Systemic Lupus Erythematosus
  • Sjögren’s Syndrome
  • Myasthenia Gravis
  • Celiac Disease
  • Vitiligo

Immunodeficiency Disorders

In these conditions, the immune system’s ability to defend against pathogens is compromised, either due to genetic disorders or acquired conditions like HIV/AIDS. This leaves the body vulnerable to infections and diseases it would typically be able to fend off. Some examples of immunodeficiency disorders include:

  • Primary Immunodeficiency Disorders (like Severe Combined Immunodeficiency)
  • Acquired Immunodeficiency Syndrome (AIDS)
  • Selective IgA Deficiency
  • Chronic Granulomatous Disease

Allergic Disorders

These disorders are characterized by the immune system’s exaggerated response to typically harmless substances in the environment, known as allergens. This hypersensitivity leads to inflammation and various symptoms in different parts of the body. Some examples of allergic disorders include:

  • Allergic Asthma
  • Rhinitis (hay fever)
  • Food Allergies
  • Atopic Dermatitis (Eczema)

Infections

These are diseases caused by invading pathogens like bacteria, viruses, and fungi, against which the immune system fights. When the immune defense is unable to completely eradicate these invaders, infection can occur.

  • Influenza
  • Pneumonia
  • Tuberculosis
  • Hepatitis B and C

Overactive vs Underactive Immune System

The immune system’s primary function is to protect the body from harmful substances, but sometimes it can either overreact or underreact, leading to health issues. A compromised or weak immune system must be properly addressed, in either scenario.

  • An overactive immune system can result in allergies, asthma, and autoimmune diseases, where the immune system mistakenly attacks healthy cells, mistaking them for harmful invaders.
  • An underactive immune system, known as immunodeficiency, leaves the body more susceptible to infections and diseases because it lacks the necessary defenses to fight off bacteria, viruses, and other harmful pathogens.

How to Boost the Immune System

If you’re looking for an immune system booster, oftentimes the best strategies are natural home remedies. Here are the best ways to reduce inflammation, enhance immune system function, and get natural pain relief.

Nutrition and Hydration

A balanced diet with immune-boosting foods and sufficient hydration plays a key role in maintaining a healthy immune system.

  • Eat a variety of fruits and vegetables: These antioxidant foods provide a range of nutrients and antioxidants that can help boost the immune system.
  • Stay well-hydrated: Proper hydration helps maintain body functions, including the immune system.
  • Consume lean proteins: Proteins are essential for building and repairing body tissues and cells, including those of the immune system.
  • Include whole grains in your diet: Whole grains are a good source of fiber, which can help to regulate your immune response.
  • Limit processed foods: These often contain preservatives and additives that may negatively affect immune health.

Lifestyle and Habits

Adopting healthy lifestyle habits can significantly contribute to enhancing your immune system.

  • Regular exercise: Physical activity can boost your immune system by promoting good circulation.
  • Adequate sleep: During sleep, your immune system releases proteins that help promote healing and stress regulation.
  • Limit alcohol consumption: Heavy drinking can negatively affect the immune system, making you more prone to infections.
  • Avoid smoking: Tobacco smoke can impair the immune system, increasing vulnerability to various diseases.
  • Manage stress: Chronic stress can weaken the immune system, so stress management techniques like meditation or yoga can help.

Hygiene and Prevention

Proper hygiene and preventive measures are critical in protecting against harmful pathogens that can weaken the immune system.

  • Regular hand washing: This basic hygiene practice can help prevent the spread of germs and strengthen your immune system.
  • Maintain oral hygiene: Good oral health can prevent harmful bacteria from entering the body and compromising your immune system.
  • Vaccination: Certain immunizations can protect you against various diseases and help your immune system respond more effectively.
  • Avoid close contact with sick individuals: This can minimize your exposure to harmful pathogens that could weaken your immune system.
  • Use tissues or elbows when coughing or sneezing: This prevents the spread of pathogens into the environment.

Use Dietary Supplements

Supplementing your diet with certain nutrients and botanicals can support the immune system, filling nutritional gaps and providing additional immune-boosting properties. Some of these antioxidant supplements and immune system vitamins are:

  • Turmeric: Known for its anti-inflammatory and antioxidant properties, turmeric can help modulate the immune system. Learn more about the best turmeric supplement.
  • Apple cider vinegar: While research is still ongoing, some studies suggest that apple cider vinegar can support immune health by promoting healthy gut bacteria and pH levels. Learn more about the best apple cider vinegar gummies.
  • Elderberry: Often used in herbal remedies for colds and flu, elderberry boosts the immune system, thanks to its rich antioxidant content. Learn more about the best elderberry gummies.
  • Vitamin C: A key nutrient for immune function, vitamin C helps stimulate the production of white blood cells and acts as an antioxidant, protecting these cells from damage.
  • Berberine: some studies suggest that berberine may support immune health by its potential to modulate inflammatory pathways and enhance antioxidant activity. Explore further about the best berberine supplements.
  • Zinc: Crucial for normal development and function of immune cells, zinc supplementation can support immune health, particularly in deficient people.

Immune System Function: Final Thoughts

From the diverse array of immune cells to the intricate mechanisms by which they identify and eliminate pathogens, the immune system is a marvel of biological defense. Exploring the potential diseases that can arise when the immune system falters highlights the importance of maintaining a balanced and resilient immune response.