Introduction to the Adaptive Immune System
Clonal Deletion and Selection
Discussed as part of the adaptive immune system.
Explains how B cells and T cells recognize and destroy specific pathogens, adapting to the environment over time.
Types of T Cells
Cytotoxic T Cells
Function: Kill other cells (toxic).
Mechanism: Produce toxic agents and chemicals to destroy infected or diseased cells in the organism.
Helper T Cells
Function: Stimulate B cells to make antibodies and activate other T cells.
Role: Act as signals for both T cells and B cells to respond appropriately during an immune response.
Regulatory T Cells
Function: Suppress immune responses to prevent overreaction, which can cause excessive symptoms or harm to the body.
Example Symptoms: Fever, body aches, runny nose, and sore throat during sickness are symptoms of an overactive immune system.
Antigen Presentation (Stage Two of Adaptive Immune System)
Definition: The process in which an antigen from a digested microbe is presented on the cell surface by an MHC class II molecule.
Key Cell Types: The only cells capable of antigen presentation (APCs) via MHC class II molecules include:
Dendritic cells
Macrophages
B cells
Mechanism of Antigen Presentation:
APCs (dendritic cells, macrophages, B cells) engulf and destroy microbes, then display a piece of that microbe on their surface.
The process of how antigens are chosen is complex and not fully understood.
Purpose: To signal to the immune system that an antigen (foreign pathogen) is present and needs to be dealt with.
Activation of Helper T Cells
When a helper T cell encounters an antigen presented by an MHC class II molecule, it:
Binds to the specific antigen.
Becomes activated, proliferates by making clones, and creates a large number of cells that recognize the same antigen.
These activated helper T cells then signal and activate other immune components, including cytotoxic T cells and B cells.
Stages Three and Four of T Cells and B Cells
T Cells
Helper T Cells: Provide activation signals to other immune cells.
Cytotoxic T Cells:
Activated by helper T cells.
Hunt down and destroy infected cells and pathogens.
Regulatory T Cells:
Suppress immune response to prevent overactivity and maintain balance.
B Cells:
Become activated through interactions with already activated helper T cells (MHC class II interaction).
Upon activation, B cells can differentiate into:
Plasma Cells: Produce antibodies specific to the antigen.
Memory Cells: Last long-term to provide immunological memory against previously encountered pathogens.
Importance of B Cell Activation
Both B and T cell activation is crucial, as multiple stages are required for the immune system to respond effectively.
B cells require helper T cell interaction for activation to ensure that the immune system does not overreact to every antigen.
Antibodies: Definition and Structure
Definition: Antibodies (immunoglobulins) are proteins produced by plasma cells in response to an antigen.
Structure:
Composed of two heavy chains and two light chains arranged in a Y-shape.
Contains two types of regions:
Variable Regions: Unique and specific to each antibody's target antigen.
Constant Regions: Identical in all antibodies of the same type.
Each antibody monomer has two antigen-binding sites.
Classes of Antibodies
Five primary classes of antibodies (immunoglobulins):
IgG
Most prevalent in serum during infection.
Main role in secondary immune response.
IgA
Found in secretions like saliva, sweat, and breast milk; acts as a first line of defense in mucous membranes.
IgM
Largest antibody; first produced during an initial immune response.
IgD
Functions as a B cell receptor, aiding B cell activation.
IgE
Associated with allergic responses and defense against parasitic infections.
Functions of Antibodies
Opsonization: Antibodies coat pathogens, making them easier targets for phagocytosis (e.g., marking them for destruction).
Neutralization: Antibodies bind to pathogens (particularly viruses), blocking their ability to attach to host cells and cause infection.
Agglutination: Antibodies clump pathogens together to enhance phagocytosis and filtration by the immune system.
Activation of Complement: IgG and IgM can activate the complement system, leading to destruction or lysis of pathogens.
Antitoxin Properties: Antibodies can bind to toxins and neutralize them, preventing harmful effects on host cells.
Immune Response Overview
Primary Response: Characterized by a lag phase (latent period) lasting about 10 days before antibodies are produced, mainly IgM initially and later IgG.
Secondary Response: Faster and stronger due to memory cells, leading to a quicker and more substantial IgG response upon re-exposure to an antigen.
Conclusions on Immunity
Immunity occurs through memory cells generated from either prior infection or vaccination.
Vaccination is categorized into natural and artificial immunity:
Natural Active Immunity: Developing immunity from actual infection.
Natural Passive Immunity: Receiving antibodies (e.g., through breast milk).
Artificial Active Immunity: Immunization through vaccines.
Artificial Passive Immunity: Receiving pre-formed antibodies from medications (e.g., monoclonal antibodies).
Vaccination History and Importance
First true vaccine developed by Edward Jenner in 1796 against smallpox.
Vaccines can be live attenuated, killed (inactivated), or subunit (antigen components).
COVID-19 Vaccine: The first mRNA vaccine has proven to be faster, easier, and cheaper to produce than traditional vaccines, showcasing the efficiency of modern medicine.
Vaccine Safety and Monitoring
Vaccines undergo rigorous development, approval, and monitoring processes to ensure safety and effectiveness.
Concerns regarding vaccine safety may stem from a lack of experience with diseases that vaccines prevent.
Ongoing monitoring is crucial to identify any long-term effects post-vaccination, although data shows mRNA vaccines have lower side effects compared to traditional vaccines.