Module 6 - Adaptive and Specific Immunity

Adaptive/Specific Immunity

• Adaptive immunity is a specific immune response to antigens
• Objectives include defining antigens, explaining how T and B cells arise and their roles, defining antibodies and their function, defining antibody-mediated (humoral) and cell-mediated immunity, discussing primary and secondary responses to antigens, and explaining active and passive immunity acquisition (naturally and artificially).

Overview of Body Defenses

• Innate defenses include surface barriers (skin, mucous membranes) and internal defenses (phagocytes, natural killer cells, inflammation, antimicrobial proteins, fever).
• Adaptive defenses include humoral immunity (B cells) and cellular immunity (T cells).

Characteristics of Specific Defenses

• Able to identify foreign antigens (molecules)
• Antibody generating
• Specific response to destroy the foreign microbe
• This system has a memory.

Cells of the Immune Response

• Lymphocytes (B & T cells) are primary cells in the immune system, capable of recognizing and responding to specific antigens.
• They distinguish self from non-self (foreign) proteins and generate responses.
• Antigen-presenting cells include macrophages and dendritic cells.

The Immune Response (Video)

• The video provides an overview of innate and adaptive immune defenses.
• Students should read the next slide before viewing the video.

Lymphocyte Development, Maturation, and Activation

• B and T lymphocytes originate in red bone marrow.
• T cells mature in the thymus, B cells mature in bone marrow.
• Lymphocytes develop immunocompetence and self-tolerance during maturation.
• Immunocompetent but naive lymphocytes leave the thymus and bone marrow, seeding secondary lymphoid organs and circulating through blood and lymph.
• Lymphocytes become activated when encountering an antigen, proliferate, and differentiate into effector cells and memory cells. Memory cells and effector T cells continuously circulate in blood, lymph, and secondary lymphoid organs.

What are B Lymphocytes?

• B lymphocytes secrete antibodies, effective against microorganisms in extracellular fluids.
• They originate in fetal bone marrow, migrating to fetal liver and lymphoid tissues to mature.
• B cells are activated during an immune response, differentiating into plasma cells (secreting antibodies) and memory cells. They constitute 10-20% of circulating lymphocytes.

What are T Lymphocytes (T cells)?

• T lymphocytes originate in bone marrow and mature in the thymus.
• They constitute 60-70% of circulating lymphocytes, and include helper T cells (CD4+), cytotoxic T cells(CD8+), and suppressor T cells.
  • Helper T cells (CD4+) secrete cytokines, regulate the immune response, and activate other T and B cells.
  • Cytotoxic T cells (CD8+) kill virus-infected and cancer cells.
  • Suppressor T cells dampen down responses and eliminate microorganisms living inside cells (intracellular).

Two Forms of Acquired Immunity

• Antibody-mediated immunity (humoral): involves B lymphocytes producing antibodies.
• Cell-mediated immunity: involves T lymphocytes destroying pathogens or non-self substances.

Antibody-Mediated (Humoral) Immunity

• Primary response: initial encounter with antigen triggers B cell activation and clonal proliferation
• B Cells proliferate into plasma cells and memory cells.
• Plasma cells secrete antibodies, which target the antigens.
• Memory B cells are primed to respond rapidly to the same antigen subsequently encountering it. Secondary response: More rapid and potent response on subsequent antigen exposure, due to memory cells.

Major Types of T Cells

• T cell development and maturation are explained graphically.

Simplified Summary of Primary Immune Response

• The primary response to an antigen involves the activation, proliferation, and differentiation of immune cells to eliminate the antigen, resulting in a legacy of antibodies and memory cells.

Specific Immunity Acquisition

• Active immunity (body produces Abs): gained through infection or vaccination and includes immunological memory.
• Passive immunity (Abs are given): gained from the mother (placenta/colostrum) or donor and characterized by a short lifespan without immunological memory.

Immunization

• Immunization is the induction of immunity artificially through exposure to a vaccine containing antigens (from pathogens).

Types of Vaccines

• Vaccines can be produced using different approaches: killed/inactivated whole bacterial cells or viruses, live attenuated bacteria or viruses, inactivated bacterial toxins, and parts of bacterial cells or viruses.

Vaccination Types

• Vaccination types include inactivated viruses, live/attenuated bacteria, toxoids, and microbial subunits, and address diseases like cholera, typhoid, influenza, rabies, polio (IPV), hepatitis A, tuberculosis, tetanus, diphtheria, measles, polio (Sabin), mumps, rubella, smallpox, rotavirus, chickenpox, haemophilus infections, pneumococcal infections, meningococcal infections, hepatitis B, and whooping cough.

Overview - Body Defenses

• The front-line defenses may fail, then the inflammatory response attempts to stop the antigen from spreading and multiplying. Failing this, the B-cell humoral response mounts an attack on the antigen, taking 4-5 days. It leaves a legacy of antibodies and memory cells used to fight future invasions. Finally, T-cells support the B-cell response and initiate a cell-mediated immune response if the pathogen has already invaded tissue cells.

Review of Defenses against Diseases

• Non-specific defenses represent the first and second lines of defense.
• Specific defenses (the third line of defense) involve B lymphocytes (memory cells, plasma cells producing antibodies) and T lymphocytes (helper T cells, cytotoxic T cells for eliminating pathogens, and memory cells).
• Failure of all defense lines leads to disease.

Explore adaptive immunity as a specific response to antigens. Learn about the roles of T and B cells, antibody function, and different types of immunity like humoral and cell-mediated. Understand primary and secondary responses, and active versus passive immunity acquisition.