“Acquired immunity is the body’s learned defense that develops after exposure to diseases or vaccines.”

Acquired immunity, also known as adaptive immunity, is the type of resistance that develops in an individual after exposure to a particular pathogen, antigen, or vaccine. Unlike innate immunity, which is present from birth and offers general protection, acquired immunity is specific and has memory. It enables the immune system to recognize, attack, and remember specific foreign invaders, providing stronger and faster protection upon future encounters. This defense mechanism is based on the coordinated actions of lymphocytes, mainly B cells and T cells, and the substances they produce, such as antibodies and cytokines.

When a pathogen enters the body for the first time, the immune system identifies its antigens and activates B cells to produce antibodies specifically designed to neutralize that pathogen. These antibodies bind to antigens and mark them for destruction by other immune cells. This initial response is known as the primary immune response, which takes several days to develop fully. During this process, memory B and T cells are also formed and stored in the body. These cells remain vigilant for years, sometimes for life, ready to respond quickly if the same pathogen attacks again. When re-exposure occurs, these memory cells trigger a much faster and stronger secondary immune response, often preventing illness altogether.

Acquired immunity is classified into two main types: active and passive immunity. Active immunity develops when a person’s own immune system is exposed to antigens and produces antibodies in response. It can occur naturally, after infection, or artificially, through vaccination. For example, recovering from measles or receiving the measles vaccine both provide active acquired immunity. In contrast, passive immunity is temporary and results from the transfer of ready-made antibodies from another source. Natural passive immunity occurs when maternal antibodies pass to the fetus through the placenta or to the newborn via breast milk, while artificial passive immunity occurs when antibodies are injected into a person to provide immediate protection, such as in cases of rabies or tetanus exposure.

One of the most remarkable features of acquired immunity is immunological memory. This property ensures that once the immune system has encountered a specific pathogen, it can remember it and mount a faster, more efficient defense upon re-exposure. This is the scientific basis behind vaccinations, which safely expose the immune system to harmless or weakened antigens, training it without causing disease.

Overall, acquired immunity is an essential component of the immune system that combines precision, adaptability, and memory. It represents the body’s intelligent defense mechanism, protecting us from countless infectious diseases throughout life while forming the foundation of modern immunology and vaccination programs.

1. SUBJECT TITLE: IMMUNOLOGY AND MICROBIAL GENETICS SUBJECT CODE : 22MBPHCT2 TITLE: ACQUIRED IMMUNITY SUBMITTED TO, Dr.S.VISWANATHAN,MSc,Ph.D., HEAD AND ASSOSIATE PROFESSOR, PG & RESEARCH DEPARTMENT OF MICROBIOLOGY SRI PARANAJALYANI COLLEGE AKWARKURICHI- 627412 SUBMITTED BY, J.KAIYA || M.SC MICROBIOLOGY PG & RESEARCH DEPARTMENT OF MICROBIOLOGY SRI PARANAJALYANI COLLEGE AKWARKURICHI- 627412

2. ACQUIRED IMMUNITY

3. CONTENTS : AIM OBJECTIVES IMMUNITY ACQUIRED IMMUNITY TYPES OF IMMUNITY -(ACTIVE, PASSIVE) DIFFERENCE BETWEEN ACTIVE AND PASSIVE COMPONENTS OF ACQUIRED IMMUNITY REFERENCE

4. 🎯 AIM To understand the concept, types, and mechanisms of acquired immunity and its role in protecting the body against specific pathogens.

5. 1. To define acquired immunity and differentiate it from innate immunity. 2. To explain the roles of B cells and T cells in adaptive immune responses. 3. To describe the types of acquired immunity: natural vs artificial, active vs passive. 4. To illustrate how vaccines help develop long-term immunity. ✔️ OBJECTIVES:

6. Immunity is the body’s defense system that protects us from diseases caused by microbes, and other harmful substances. Types of Immunity: 1. Innate Immunity Present from birth, acts fast and is the first line of defense (e.g., skin, fever, white blood cells). 2. Acquired (Adaptive) Immunity Develops after exposure to pathogens or vaccines. It is specific and has memory (involves B cells and T cells). Acquired immunity is further divided into: ⭐Active immunity Body makes its own antibodies (e.g., after infection or vaccination). ⭐Passive immunity Antibodies are given (e.g., from mother to baby or injected).

7. INNATE IMMUNITY ADAPTIVE IMMUNITY Innate immunity refers to a naturally occurring immunity by the genetic constituents and the physiology of a person Adaptive immunity refers to an acquired immunity, mediated by T cells and B cells and characterized by an immunological memory Known as natural immunity Known as acquired immunity Generates a non-specific immune response Generates a specific immune response Always present in the body Generated in response to exposure to an externa l factor Generates a rapid response Delayed 5-6 days Plasma proteins, phagocytes , physical and chemical barriers are the components Humoral and cell-mediated immunity are the components Temperature, pH, skin, and mucous membranes are the barriers Lymph nodes, spleen, and lymphoid tissues are the barriers Does not develop memory cells Develops memory cells Possesses a less diversity Possesses a higher diversity Less potent Exhibits a higher potency Does not produce allergic reactions Develops allergic reactions ; immediate and delayed hypersensitivity Ex: Redness and swelling caused by the white blood cells around a wound Ex: Vaccination against a virus Innate vs Adaptive Immunity

8. ACQUIRED IMMUNITY Specificity – Adaptive immunity recognizes and responds to specific antigens with high precision, unlike innate immunity which is broad. Diversity – It can generate a vast repertoire of antigen receptors to recognize millions of different antigens. Memory – Once exposed to an antigen, the immune system “remembers” it and mounts a faster, stronger response upon re-exposure. Self vs Non-Self Recognition – Adaptive immunity can distinguish between the body’s own cells and foreign antigens, preventing autoimmunity under normal conditions. Clonal Selection – When lymphocytes encounter their specific antigen, they proliferate (clonal expansion) and differentiate into effector and memory cells.

9. ACQUIRED IMMUNITY Effector Functions – It employs both cellular (T-cell mediated) and humoral (antibody-mediated by B cells) responses to eliminate pathogens. Antigen Specific Receptors – B cells express BCRs (membrane-bound antibodies) and T cells express TCRs, which provide antigen recognition. Inducibility – Unlike innate immunity, adaptive immunity must be triggered by exposure to antigen and takes time to develop (lag phase). Specialization – The system tailors responses depending on the pathogen type (e.g., different responses for intracellular vs extracellular microbes). Regulation – Adaptive responses are tightly regulated to prevent overreaction (immunopathology) and maintain tolerance.

10. ACQUIRED IMMUNITY ACTIVE IMMUNITY PASSIVE IMMUNITY NATURAL NATURAL ARTIFICIAL ARTIFICIAL Immunity that develops during your lifetime Develops in response to an Infection or vaccination Develops after you receive antibodies from someone or Somewhere else Antibodies developed in response to an Infection Antibodies developed in response to a Vaccination Antibodies recived from mother Ex, breast milk Antibodies received from a medicine, e.g from Gamma globulin injection or infusion Immunity after recovering from measles, chickenpox, or COVID-19 infection. Immunity after receiving polio vaccine, tetanus toxoid, or hepatitis B vaccine. Maternal IgG crossing placenta; IgA in breast milk. Rabies immunoglobulin, antivenom for snake bite, diphtheria antitoxin.

11. ACTIVE IMMUNITY PASSIVE IMMUNITY Produced actively by host immune system Immunoglobulins received passively Induced by: Infection (natural) Vaccination (artificial) Acquired by: Mother to fetus IgG transfer (natural) Readymade antibody transfer (artificial) Lag period present No lag period Memory present Memory present Booster doses are useful Subsequent doses are less effective Negative phase may occur No negative phase Not useful in immunodeficiency Useful in immunodeficiency Difference between Active immunity and Passive immunity

12. Active immunity Active immunity is the resistance developed in an individual when their own immune system is exposed to an antigen , leading to the activation of lymphocytes, production of antibodies, and formation of immunological memory. Active immunity is the resistance developed by an individual in response to an antigen entering the body either by natural infection or through vaccination. It is not inherited.It is caused by infections or vaccines. Active acquired immunity is of two types, namely natural active acquired immunity and artificial active acquired immunity. Natural active acquired immunity is caused by infection. Artificial active acquired immunity is caused by vaccine.

13. The antigen stimulates the immune system of the host. Humoral and cell mediated immune responses are produced. Antibodies are produced by B cells.Lymphokines are produced by T cells. Memory cells are produced. Secondary immune response is produced. Inmunity persists life long and permanent. Types of Active immunity 1. Natural active immunity 2. Artificial active immunity

14. NATURAL ACTIVE IMMUNITY Natural active immunity is the resistance developed by the body after exposure to a natural infection, where the host’s own immune system produces antibodies and memory cells. Occurs after natural infection – body produces its own immune response. Provides immunological memory – protects against future infections. Often long-lasting – especially after many viral diseases. Can be lifelong – some infections give permanent protection. Varies with the pathogen – viral infections usually give stronger immunity than bacterial infections. EXAMPLE ; Measles infection: When a person gets measles, the immune system responds by producing specific antibodies and memory T/B cells. After recovery, these memory cells remain in the body for life, so the person usually does not get measles again.

15. ARTIFICIAL ACTIVE IMMUNITY Artificial active immunity is the protection developed by the body after exposure to antigens through vaccination , where the immune system produces its own antibodies and memory cells without suffering from the disease. Induced artificially – by vaccines, not natural infection. Body produces antibodies & memory cells – long-term protection. Mild or no symptoms – since the pathogen is weakened, killed, or only parts are used. Boosters may be required – to maintain immunity (e.g., tetanus). Prevents epidemics – important for public health and herd immunity. EXAMPLES : Tetanus vaccine (Toxoid vaccine): The tetanus vaccine contains an inactivated toxin (toxoid) of Clostridium tetani. When injected, the body produces specific antibodies and memory cells against the toxin. Later, if the person is exposed to the tetanus bacteria, their immune system can quickly neutralize the toxin, preventing the disease .

16. Types of Artificial Active Immunity (Vaccines) 1. Live Attenuated Vaccines : Weakened but living microbes that can still multiply without causing disease. Mechanism: The weakened microbes enter the body, multiply slightly, and trigger a strong immune response, producing antibodies + memory cells. Example: MMR vaccine (Measles, Mumps, Rubella). 2. Inactivated (Killed) Vaccines : Microbes killed by heat/chemicals; cannot multiply. Mechanism: The killed microbes expose their antigens to the immune system, which produces antibodies. Since they can’t replicate, booster doses are needed to strengthen memory. Example: Polio (Salk) vaccine.

17. Types of Artificial Active Immunity (Vaccines) 3. Toxoid Vaccines : Made from inactivated toxins (toxoids) produced by bacteria. Mechanism: The toxoid stimulates the body to make antibodies against the toxin. If the real toxin enters later, antibodies neutralize it quickly. Example: Tetanus toxoid vaccine. 4. Subunit / Recombinant Vaccines : Contain only specific antigenic parts of the pathogen (proteins/sugars). Mechanism: The immune system recognizes these fragments as foreign, produces antibodies and memory cells without risk of infection. Example: Hepatitis B vaccine (made using recombinant DNA technology).

18. Passive immunity: Passive immunity is the transfer of preformed antibodies (or immune cells) from one individual to another, giving immediate but short-lived protection, without the recipient’s immune system generating its own response or memory. The resistance developed by a non - immune individual by receiving antibodies or sensitized lymphocytes from an immune individual is known as passive immunity. The antibodies or sensitized cells are transferred from immunized host to a non immunized host. In passive immunity, the host does not produce immune response.The host does not produce antibodies or sensitized cells. The host does not produce resistance.There is no primary or secondary response

19. Passive immunity Types of Passive immunity 1. Natural passive immunity 2. Artificial passive immunity Memory cells are not produced. The protection is immediate. The protection is temporary lasting for only a few days or weeks. Passive immunity works out better in AIDS patients. It is less effective and inferior to active immunity.

20. NATURAL PASSIVE IMMUNITY Natural passive immunity is the immunity transferred from mother to child naturally , without the child’s immune system producing its own antibodies. It provides immediate but temporary protection. Placental Transfer – Maternal IgG antibodies cross the placenta to the fetus during pregnancy. Colostrum and Breast Milk – Maternal IgA antibodies in milk protect the newborn’s gut and respiratory tract. EXAMPLE: Maternal IgG transfer (placenta): During pregnancy, the mother’s IgG antibodies cross the placenta and enter the fetal circulation. These antibodies protect the newborn against diseases like measles, tetanus, and diphtheria for the first few months of life until the baby develops its own immunity. Provides immediate protection to the newborn. No memory is formed because the baby’s immune system is not activated. Short-lived immunity (lasts weeks to months). Protects infants at a time when their immune system is still immature.

21. ARTIFICIAL PASSIVE IMMUNITY The development of resistance in a patient by transferring antibodies or immunized lymphocytes from a donor is known as artificial passive immunity. Artificial passive immunity is therapeutically used in the treatment of tetanus, diphtheria, gas gangrene, snake bite and immunodeficiency diseases. Artificial passive immunity is brought about by using anyone of the fol-lowing methods: 1. Hyperimmune serum of animal or human origin 2. Convalescent serum 3. Pooled sera from different healthy individuals 4. Combined immunization 5. Adoptive immunity.

22. ARTIFICIAL PASSIVE IMMUNITY eonatal . Of new born babies conventionally limited to the first 4 weeks of life. Therapeutics - Science of treating disease. Gas gangrene - A complication of the severe wounds where tissue is crushed to death. Bacteria grow in these tissues and also spread to healthy tissues which are decomposed with the elimination of gas. Types of Artificial Passive Immunity 1. Hyperimmune Serum (Antiserum) of Animal or Human Origin Ready-made antibodies are collected from humans or animals that were immunized against a disease. When injected, they give immediate protection. Example: Anti-rabies serum, Anti-tetanus serum, Anti-venom for snake bites.

23. TYPES OF ARTIFICIAL PASSIVE IMMUNITY 2. Convalescent Serum Serum taken from a person who has recovered from a disease, containing antibodies against that pathogen. It is given to another patient for protection. Example: Convalescent plasma used during COVID-19 pandemic, also used for Ebola. 3. Pooled Sera from Different Healthy Individuals Serum collected from many healthy people, pooled together, and given as a source of broad protective antibodies. Provides general short-term protection. Example : Normal human immunoglobulin (IVIG) used for hepatitis A exposure or for immunodeficient patients.

24. TYPES OF ARTIFICIAL PASSIVE IMMUNITY 4. Combined Immunization A person is given both passive antibodies and active vaccine at the same time. Passive immunity → gives immediate protection. Active vaccine → develops long-term protection. Example: Rabies exposure → Anti-rabies serum (passive) + Rabies vaccine (active). 5. Adoptive Immunity Transfer of immune cells (lymphocytes or stem cells) from a donor to a recipient. The transferred cells provide immunity by producing antibodies or attacking pathogens. Example: Bone marrow transplant in immunodeficient patients, or transfer of T-cells in cancer immunotherapy.

25. HERD IMMUNITY Herd immunity means when most people in a population are immune (by vaccine or past infection), the spread of disease becomes very low and even unprotected people get indirect protection. Threshold needed: A certain % of people must be immune (depends on disease, e.g. measles needs ~95%). Indirect protection: Even babies, old people, or sick people (who can’t take vaccine) are protected. By vaccine or natural infection : Vaccination is safer than natural infection to achieve herd immunity. EXAMPLES : Measles: Needs 95% vaccinated → no big outbreaks. Polio: With 80–85% vaccination, polio almost disappeared worldwide. COVID-19: Vaccines helped reduce spread, but new variants made full herd immunity harder. When many people develop acquired immunity (through vaccination or natural infection), the whole group gains herd protection.

26. COMPONENTS OF ACQUIRED IMMUNITY B cells → A type of lymphocyte that develops in the bone marrow. It produces antibodies and plays a key role in humoral immunity. T cells → A type of lymphocyte that matures in the thymus. It directly attacks infected cells and is essential for cell-mediated immunity.

27. Reference : Acquired immunity | PPT https://share.google/cAwd4KX5CncbcRKwM Kuby immunology - 6th edition,chapter 1,page no - 9 to 17 Janeway’s Immunobiology (9th edition, 2017) - page ((345–470) include chapter-9,10,11 Cellular and Molecular Immunology (Abul K. Abbas, etc.) - page (109 -160) chapter- 6 to 12

28. LEARNING OUTCOMES : ✅ Define Acquired Immunity and differentiate it from innate immunity. ✅ Explain the role B cells and T cells in specific immune responses. ✅ Describe the Types of Acquired Immunity – active vs passive, natural vs artificial. ✅ Illustrate how Vaccines help develop long-term acquired immunity. ✅ Analyze the Advantages and limitations of acquired immunity in disease protection.

29. Ability to explain in simple words. Use of visuals (images/diagrams) to support presentation. Nervousness or stage fear. Limited experience in public speaking. Chance to improve communication and presentation skills. Builds confidence for future academic and job interviews. Time limitation while presenting. Stronger presenters in class may create comparison.

30. Thank You !