IMMUNE SYSTEM AND IMMUNIZATION

1. IMMUNE SYSTEM – BASIC CONCEPT

The immune system is a complex and well-coordinated network of cells, tissues, organs and molecules that protects the human body from disease-causing organisms such as bacteria, viruses, fungi, parasites and other foreign particles.

Immunity refers to the ability of the body to resist, recognize and eliminate pathogens and harmful substances. Humans are continuously exposed to microorganisms present in air, water, food and soil. Without an effective immune system, survival would not be possible.

Functions of the Immune System:
• Recognizes foreign substances (antigens)
• Destroys disease-causing organisms
• Removes damaged or abnormal cells
• Provides long-term protection through memory

2. IMMUNE RESPONSE

Immune response is the reaction of the immune system against antigens or pathogens entering the body. The primary objective of immune response is protection of the body.

Types of Immunity:
• Innate Immunity
• Acquired (Adaptive) Immunity

3. INNATE IMMUNITY (NATURAL IMMUNITY)
Innate immunity is present from birth and acts as the first line of defence. It is non-specific, meaning it responds in the same way to all pathogens.

Features:
• Present since birth
• Non-specific defence
• Acts immediately
• No memory of previous infection

Components of Innate Immunity:

A. Physical Barriers
• Skin: Acts as a physical shield. Dryness, shedding of skin and acidic pH prevent microbial growth.
• Mucous membranes: Trap pathogens in respiratory, digestive and urogenital tracts.
• Cilia in nasal passages trap dust and microbes and push them out.

B. Physiological / Chemical Barriers
• Hydrochloric acid in stomach kills most microbes entering with food.
• Saliva, sweat and tears contain enzymes like lysozyme that destroy bacteria.

C. Cellular Barriers – White Blood Cells (WBCs)
WBCs originate in bone marrow and circulate in blood.

Important WBCs:
• Neutrophils: First responders to infection; engulf pathogens.
• Monocytes: Convert into macrophages in tissues; destroy microbes and dead cells.
• Eosinophils: Kill parasites and secrete toxic substances.
• Basophils: Release histamine during allergic reactions causing inflammation.

D. Cytokines
Cytokines are chemical messengers produced by immune cells.
Functions:
• Activate immune cells
• Regulate immune response
• Help in inflammation

Interferons:
• Special cytokines with antiviral action
• Prevent viral replication inside cells

 
4. ACQUIRED (ADAPTIVE) IMMUNITY
 Acquired immunity develops after exposure to a pathogen or vaccination. It is highly specific and has memory.

Key Features:
• Specific to antigen
• Develops slowly in first exposure
• Has immunological memory

Primary and Secondary Response:
• Primary response: First exposure; slow and weak
• Secondary response: Subsequent exposure; rapid and strong due to memory cells

Cells Involved:
• B-Lymphocytes
• T-Lymphocytes

A. B-Lymphocytes (Humoral Immunity)
• Produce antibodies
• Antibodies circulate in blood and lymph
• Responsible for antibody-mediated immunity

Memory B Cells:
• Long-lived cells
• Provide long-term immunity
• Responsible for rapid response during reinfection

B. T-Lymphocytes (Cell-mediated Immunity)
• Do not produce antibodies

Types:
• Helper T Cells: Activate B cells, macrophages and killer T cells
• Killer (Cytotoxic) T Cells: Destroy virus-infected and cancer cells

5. ANTIGEN AND ANTIBODY

Antigen:
• Any foreign substance that triggers immune response
• Has specific markers recognized by antibodies

Antibody:
• Also called immunoglobulin
• Y-shaped protein
• Binds specifically to antigen
• Neutralizes pathogens or marks them for destruction

6. IMMUNIZATION

Immunization is the process of providing immunity against a disease by administering vaccines.

Importance:
• Prevents life-threatening diseases
• Saves 2–3 million lives annually worldwide
• Protects individuals and community (herd immunity)

7. VACCINES

Vaccines are biological preparations containing weakened, killed or parts of pathogens that stimulate immune response without causing disease.

Mechanism of Action:
• Vaccine introduces antigen into body
• Immune system produces antibodies
• Memory cells are formed
• On real infection, rapid immune response occurs

Booster Dose:
• Required in some vaccines to maintain immunity

TYPES OF VACCINES

• Live Attenuated Vaccines: Weakened living microbes (e.g. measles)
• Inactivated Vaccines: Killed microbes (e.g. polio – IPV)
• Subunit Vaccines: Only antigenic parts used
• Toxoid Vaccines: Inactivated toxins (e.g. tetanus)
• Conjugate Vaccines: Polysaccharide antigen linked with protein
• Gene Vaccines: Pathogen genes introduced
• Recombinant Vector Vaccines: Produced using recombinant DNA technology
CHALLENGES OF VACCINATION IN INDIA

• Lack of awareness and education
• Religious and social misconceptions
• Inadequate health infrastructure
• Shortage of trained health workers
• Cold chain storage issues
• Poor last-mile delivery in rural areas
• Insufficient monitoring of coverage
• Sparse population and difficult terrain

WAY FORWARD 

• Strengthening Universal Immunization Programme
• Awareness campaigns and community participation
• Improving cold chain infrastructure
• Training frontline health workers
• Digital monitoring and tracking systems
• Addressing vaccine hesitancy through trust-building

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Subject: Science

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