Q.Differentiate the following and give examples of each:

Here is a differentiation of the given immunity types:

(a) Innate and acquired immunity

• Innate immunity is a non-specific type of defense present from birth, acting as the body's first line of defense against all pathogens. It includes physical barriers (skin, mucous membranes), physiological barriers (stomach acid, tears), cellular barriers (phagocytes like neutrophils and macrophages), and cytokine barriers (interferons). This immunity does not develop memory.
• Acquired immunity is pathogen-specific and develops after exposure to a particular pathogen. It is characterized by its ability to recognize specific antigens and remember past encounters, leading to a faster and stronger response upon subsequent exposure. This immunity is primarily mediated by B and T lymphocytes.

(b) Active and passive immunity

• Active immunity is generated when an individual's own immune system produces antibodies in response to an antigen. This process is slow to develop but provides long-lasting protection and immunological memory. Examples include immunity acquired after a natural infection or through vaccination. …

Our body possesses a remarkable defence system, known as the immune system, which protects us from various disease-causing organisms. This system is broadly categorised into different types based on how immunity is acquired and its specificity towards pathogens. Understanding these distinctions is crucial for grasping the full scope of human health and disease.

(a) Innate and Acquired Immunity

The fundamental difference between innate and acquired immunity lies in their specificity and whether they are present from birth or developed later.

Innate Immunity

Innate immunity is the body's first line of defence, present from birth. It is a non-specific type of defence, meaning it acts against all foreign agents in a general manner, without distinguishing between different pathogens. This immunity provides various types of barriers to prevent the entry of foreign agents into the body. It offers immediate protection and does not involve any memory of past encounters with pathogens.

The barriers provided by innate immunity include:

• Physical Barriers: These prevent the entry of microorganisms.
  • The skin is the main physical barrier, preventing the entry of most microorganisms.
  • Mucous membranes lining the respiratory, gastrointestinal, and urogenital tracts trap microbes and prevent their entry.
• Physiological Barriers: These are secretions that inhibit microbial growth.
  • Acid in the stomach kills many pathogens ingested with food.
  • Saliva in the mouth and tears from the eyes contain enzymes (like lysozyme) that can destroy bacteria.
• Cellular Barriers: Certain types of white blood cells act as cellular barriers.
  • Phagocytic cells like neutrophils (polymorpho-nuclear leukocytes), monocytes, and natural killer (NK) cells in the blood, as well as macrophages in tissues, engulf and destroy microbes.
• Cytokine Barriers: These are proteins secreted by virus-infected cells.
  • Interferons, for example, are secreted by virus-infected cells and protect non-infected cells from further viral infection.

Acquired Immunity

Acquired immunity, also known as adaptive immunity, is pathogen-specific and develops during an individual's lifetime. Unlike innate immunity, it has the unique ability to recognise specific pathogens, remember them, and mount a more robust response upon subsequent encounters. This memory is a hallmark of acquired immunity.

When our body encounters a pathogen for the first time, it mounts a primary response, which is of low intensity and takes time to develop. However, subsequent encounters with the same pathogen elicit a highly intensified and rapid secondary or anamnestic response. This is due to the memory cells generated during the primary response.

Acquired immunity is mediated by specialised lymphocytes:

• B-lymphocytes (B-cells): These produce proteins called antibodies in response to pathogens. Antibodies circulate in the blood and lymph, targeting and neutralising pathogens. This is known as Humoral Immunity or Antibody-Mediated Immunity (AMI).
• T-lymphocytes (T-cells): These do not secrete antibodies but directly attack infected cells or help B-cells produce antibodies. This is known as Cell-Mediated Immunity (CMI).

Here is a summary of the differences:

(b) Active and Passive Immunity

Active and passive immunity are two ways in which acquired immunity can be gained, differing in whether the body actively produces antibodies or receives them pre-formed.

Active Immunity

Active immunity is developed when an individual's own body produces antibodies in response to an antigen. This process takes time to develop, but it results in long-lasting immunity because the body creates memory cells.

Active immunity can be acquired in two ways:

• Natural Active Immunity: This occurs when a person is naturally exposed to a pathogen and recovers from the infection. The immune system then produces antibodies and memory cells against that specific pathogen.
  • Example: Immunity developed after recovering from diseases like chickenpox or measles.
• Artificial Active Immunity: This is induced through vaccination. Vaccines contain weakened or killed pathogens, or their antigenic parts, which stimulate the immune system to produce antibodies and memory cells without causing the disease.
  • Example: Immunity developed after receiving vaccines for polio, BCG (tuberculosis), or tetanus toxoid.

Passive Immunity …

Method: Two Yes/No Questions (Decision-Tree)

Instead of building out full tables for both pairs, this method reaches the same

classification with just two questions asked in sequence — useful for quickly deciding

which category an unfamiliar example belongs to.

Question 1 — "Does this defence require the body to have met the pathogen before?"

• No → it is innate immunity: present from birth, non-specific, acts the same way against any pathogen (skin, stomach acid, phagocytes, interferons).
• Yes → it is acquired immunity: pathogen-specific, develops only after exposure, and carries memory. Proceed to Question 2 to classify it further.

Question 2 (only for acquired immunity) — "Did THIS body make its own antibodies, or did it receive ready-made ones from elsewhere?"

• Made its own → active immunity (slow to build, long-lasting, has memory) — whether from recovering from an infection naturally, or from a vaccine artificially.
• Received ready-made antibodies → passive immunity (immediate, short-lived, no …