Immunity: Your Body’s Powerful Defence Network

4 Types of Immunity

When discussing the 4 types of immunity, we broadly classify them into:

1. Innate Immunity (also called Natural or Non-specific Immunity)

2. Acquired Immunity (also called Adaptive Immunity)

3. Active Immunity

4. Passive Immunity

While innate and acquired are the two main categories, active and passive immunity also play crucial roles. Let us discuss these types of immunity in more detail below.

Innate Immunity

Innate immunity is present from birth and acts as the first line of defence. It responds instantly to any pathogen attempting to invade the body. This defence system includes various barriers and cells that work collectively to prevent, detect, and destroy foreign agents before they can cause harm.

Key Barriers in Innate Immunity

1. Physical Barriers

• Skin: Acts as a tough outer shield preventing pathogens from entering.

• Body Hair and Cilia: Trap dust particles and microbes.

• Mucus in the respiratory and digestive tracts traps microbes before they can invade deeper tissues.

2. Physiological Barriers

• Stomach Acid (Hydrochloric Acid): Creates a highly acidic environment that kills pathogens in food or water.

• Saliva and Tears: Contain enzymes with antibiotic properties, limiting pathogen growth.

3. Cellular Barriers

• White Blood Cells (WBCs) such as neutrophils, lymphocytes, basophils, eosinophils, monocytes, and macrophages. These cells constantly patrol the bloodstream and tissues, ready to engulf (phagocytose) and destroy invading pathogens.

• Natural Killer (NK) Cells: Recognise and eliminate virus-infected cells or tumour cells.

4. Cytokine Barriers

• Interferons: When a virus infects a cell, the cell releases interferons that protect neighbouring cells from viral replication.

Main Cells Involved in Innate Immunity

• Phagocytes: Engulf and digest foreign particles.

• Macrophages: Release signalling molecules (cytokines) to recruit more immune cells.

• Mast Cells: Involved in wound healing; release histamine for inflammatory responses.

• Neutrophils: Release toxic granules to destroy bacteria and fungi.

• Eosinophils: Contain potent enzymes targeting parasites.

• Basophils: Release histamine and attack larger parasites.

• Dendritic Cells: Present antigens and activate other immune cells.

Acquired Immunity

Acquired immunity, also referred to as adaptive immunity, is not present at birth. It is developed over time, often after exposure to specific pathogens or through vaccination. When the immune system first encounters a pathogen, it mounts a primary response. If the pathogen appears again, it triggers a swifter, more robust secondary response due to immunological memory.

Characteristics of Acquired Immunity

1. Specificity: The immune system tailors its response to particular pathogens, recognising unique antigens and neutralising them.

2. Diversity: It can identify a vast range of pathogens, from bacteria to parasites.

3. Self vs Non-Self Recognition: Normally, immune cells distinguish between the body’s own cells (self) and foreign cells (non-self).

4. Memory:Once exposed to a pathogen, the immune system “remembers” it. Future encounters lead to a faster, more efficient response.

Cells Involved in Acquired Immunity

• B-Cells

• Produced in the bone marrow.

• When B-cells encounter an antigen, they differentiate into plasma cells that secrete antibodies.

• Antibody-driven immune response is called humoral immunity.

• T-Cells

• Originate in the bone marrow and mature in the thymus.

• Types include Helper T-cells (release cytokines to activate other cells), Cytotoxic T-cells (kill infected or cancerous cells), and Regulatory T-cells (regulate and moderate immune responses).

Active and Passive Immunity

Active Immunity

• Develops when you come into direct contact with a pathogen or receive a vaccine containing antigens.

• The body produces its own antibodies.

• Usually provides long-term protection since memory cells are generated.

Passive Immunity

• Occurs when ready-made antibodies are transferred from another source. Examples include maternal antibodies passed to a baby through breast milk or preformed antibodies given as medical treatment.

• Offers immediate but short-lived protection (since no memory cells are formed).

Also, read the Differences between Active and Passive Immunity

Autoimmunity

Autoimmunity arises when the immune system mistakenly recognises the body’s own cells as foreign and mounts an attack against them. This leads to autoimmune disorders, such as Type I diabetes or rheumatoid arthritis. Research into immunosuppressants and targeted therapies aim to reduce the autoimmune response without compromising overall immunity.

Immunity Booster Approaches

While the body’s defence systems are highly efficient, there are practical immunity booster strategies to support your innate and acquired responses:

1. Balanced Diet: A nutrient-rich diet (including vitamins C, D, and E, and minerals like zinc) supports the production and functioning of immune cells.

2. Regular Exercise: Moderate exercise enhances circulation, helps flush out toxins, and improves immune surveillance.

3. Adequate Sleep: Restful sleep is crucial for repair and regeneration, allowing the immune system to stay in top form.

4. Stress Management: Chronic stress can suppress immune function, so adopting relaxation techniques can help balance your immune responses.

5. Vaccinations: Vaccines prime your immune system to recognise and respond to specific pathogens without the risk of getting a full-blown disease.

Vaccines

Vaccines form a cornerstone of acquired immunity. They contain weakened or inactive forms of pathogens or purified antigens. Once vaccinated, your immune cells produce antibodies specific to those pathogens. As a result, subsequent exposures to the actual pathogen are swiftly neutralised. Vaccination contributes to herd immunity and has successfully eradicated or reduced many infectious diseases globally.

The Immune System: Organs and Components

The immune system is a large network composed of organs known as lymphoid organs, specialised cells, and molecules like antibodies. These organs produce, mature, and store immune cells, mainly lymphocytes.

Lymphoid Organs

1. Bone Marrow (Primary Lymphoid Organ): Production site for all blood cells, including B-cells and immature T-cells.

2. Thymus (Primary Lymphoid Organ): A small organ where T-cells mature.

3. Spleen (Secondary Lymphoid Organ): Filters the blood and destroys old or damaged blood cells. Also a site for immune cell activation.

4. Lymph Nodes (Secondary Lymphoid Organs): Small, bean-shaped structures along lymphatic vessels. Trap pathogens and activate lymphocytes.

5. Tonsils and Appendix (Secondary Lymphoid Organs): Play supportive roles in sampling pathogens entering through the mouth or digestive system.

6. Tertiary Lymphoid Organs: Contain fewer lymphocytes but can expand in response to inflammation or chronic infection.

Humoral vs Cell-Mediated Immune Response

1. Humoral Immune Response

• Mediated by antibodies produced by B-lymphocytes.

• When B-cells bind to an antigen, they become plasma cells that secrete specific antibodies. These antibodies can travel throughout the bloodstream to neutralise the pathogen.

2. Cell-Mediated Immune Response

• Involves T-cells (Helper T-cells and Cytotoxic T-cells).

• Helper T-cells release cytokines to coordinate the immune response.

• Cytotoxic T-cells directly kill infected or abnormal cells.

The Role of Microbiome and Immunotherapy

1. Gut Microbiome: Recent studies highlight how beneficial gut bacteria can shape and train our immune system. A balanced gut flora can strengthen both innate and acquired immunity.

2. Immunotherapy: Used in cancer treatment, immunotherapy leverages the body’s own immune cells or synthetic versions to target cancer cells specifically. This cutting-edge approach includes CAR T-cell therapy and checkpoint inhibitors, illustrating how flexible and powerful our immune system can be.

Interactive Quiz on Immunity

1. Which of the following is NOT a physical barrier in innate immunity?
   A. Skin
   B. Tears
   C. Body Hair
   D. Mucus

2. Which cell type is primarily responsible for antibody production?
   A. T-cells
   B. B-cells
   C. Dendritic cells
   D. Red blood cells

3. Name one example of passive immunity.
   A. Breastfeeding
   B. Vaccination
   C. Bone marrow producing antibodies
   D. Mucus secretions

4. In autoimmunity, the immune system attacks ____:
   A. Only foreign pathogens
   B. The body’s own tissues
   C. Only cancer cells
   D. None of the above

5. Where do T-cells mature?
   A. Bone marrow
   B. Thymus
   C. Spleen
   D. Lymph nodes

Check your answers

1. B. Tears (they are a physiological barrier, not a physical one)

2. B. B-cells

3. A. Breastfeeding

4. B. The body’s own tissues

5. B. Thymus