Adaptive Immunity

• Chapter 16 is about Adaptive Immunity

Overview of Adaptive Immunity

• Adaptive immunity involves recognizing and defending against specific invaders and their products
• Adaptive immunity is also known as "detective" immunity
• Attributes include specificity, memory, and a delayed functional start

Lymphocytes

• Lymphocytes are crucial for adaptive immunity
• The two main types are B lymphocytes (B cells) and T lymphocytes (T cells)

B Lymphocytes (B Cells)

• B lymphocytes mediate humoral immunity by attacking invaders outside the cell
• Function against Extracellular pathogens and toxins

T Lymphocytes (T Cells)

• T lymphocytes mediate cell-mediated immunity, attacking infected cells inside
• Function against Intracellular pathogens

Antigens

• Both T and B cells recognize antigens
• Antigens are molecules like surface proteins, carbs, or lipids recognized as foreign
• Antigens are the primary molecule the body recognizes
• There are 3 basic types of antigens

Exogenous Antigens

• Exogenous antigens are found outside a body’s cells
• Examples are toxins and components of microbial cell walls, membranes, flagella, and pili

Endogenous Antigens

• Endogenous antigens are produced by microbes that reproduce inside a body's cells

Autoantigens

• Autoantigens are self-made antigens made by our DNA

Epitopes

• Antigens are recognized by three-dimensional regions called epitopes

Major Histocompatibility Complexes (MHC)

• Epitopes are recognized by lymphocytes when displayed as Major Histocompatibility Complexes (MHC)
• MHCs are glycoproteins found in the membranes of most cells
• They hold and position epitopes for presentation to immune cells

Antigen Presenting Cell (APC)

• The cell that presents the antigen to the lymphocytes

MHC Proteins

• There are two types of MHC proteins

MHC I

• MHC I is present on all nucleated cells, except red blood cells

MHC II

• MHC II is present on antigen-presenting cells (APCs)
• APCs include macrophages, dendritic cells, and B cells
• APC's wander around and are non-stationary
• H cells could be both MHC I and MHC II

Antigen Processing

• Autoantigens are displayed as self MHC's
• Endogenous and Exogenous Antigens are processed into MHC proteins to display the pathogen epitopes

Cell Antigen Processing

• MHC I is used if a nucleated cell is fixed
• MHC I and MHC II are used when an antigen-presenting cell is involved

T Cell Receptor (TCR)

• T cells recognize pathogens displayed on MHCs
• T cells have a unique T Cell Receptor (TCR) protein for each pathogen epitope
• There is a matching TCR for every possible epitope

B Cell Receptors (BCR)

• B cells recognize pathogens displayed on MHCs
• B cells have unique B Cell Receptors (BCR) for pathogen epitopes
• Divisions of T and B cells occur after epitope recognition

Recognition

• Antigen Presenting Cells (APCs) are usually required for recognition
• APCs include macrophages, B cells, and dendritic cells

Costimulation

• Interaction between T/B cells and APCs is required to multiply T/B cells
• This interaction results in the release of surface molecules on each cell and Cytokines

Immune Response Cytokines

• Interleukins (ILs) signal among leukocytes to help communication between WBCs

Outcomes

• Recognition and costimulation lead to mass production of T/B cells to attack foreign epitopes

T Cell Activation

• T cell activation is a cell-mediated attack of infected cells

T Lymphocytes

• Types of T lymphocytes include Cytotoxic T lymphocytes, Helper T lymphocytes, Memory T lymphocytes and Regulatory T lymphocytes

Cytotoxic T Lymphocyte (T8, Tc)

• T8s, Tc, do the actual killing of cells and directly kill other cells with perforins

Helper T Lymphocyte

• Helper Ts help make the army and multiply B cells and cytotoxic T cells
• There are two types, type 1 (Th1) and type 2 (Th2)

Memory T Lymphocytes

• Memory T lymphocytes are used to remember the same epitope in the future

Regulatory T Lymphocyte

• Regulatory T lymphocyte involved w/ Autoimmune diseases and prevents self-attack
• Inhibits autoantigen attack

Important points for T Cells

• Infected cells display MHC I foreign epitopes
• APC displays both MHC I and MHC II
• Interleukin 12 is produced by the APC causing Th to become Th1
• Interleukin 2 is produced by both Th1 and Tc
• Tc now attacks infected Cells displaying MHC1 endogenous

B Cell Activation and Humoral Immunity

• Involves production of ANTIBODIES to attack extracellular epitopes

B Lymphocytes

• Initially recognize foreign epitopes and act as APC,s and become plasma cells

Plasma Cells

• Plasma cells produce antibodies
• Activated Helper T lymphocytes (T4, Th): help multiply B cells and cytotoxic T cells

Memory B lymphocytes

• The function of Memory B lymphocytes is, to remember the same epitope in the future so you wont get the same infection Again

Important points for B cells

• APC’s (both dendritic and B) displays MHC II
• Interleukin 4 causes Th to become Th2
• Interleukin 4 also causes B cell to become Plasma cells
• Antibodies from Plasma Cells attack exogenous antigens

Basic Antibody Structure

• Antibodies have 2 heavy chains and 2 light chains
• Each chain has a variable region that creates an Antigen Binding Site
• The site is epitope-specific
• The stem of the heavy chains leads to different types of antibodies

Antibodies

• IgM is the first antibody produced (acute)
• IgG is the most common and longest-lasting (chronic)
• IgA is associated with body secretions (mucous memb)
• IgE is involved in response to parasitic infections and allergies
• IgD exact function is not known
• Ig = immunoglobulin

Antibodies Actions

• Phagocytosis
• Lysis
• Agglutination (Clumping) - attaches microbes together
• Neutralize
• Antibodies don't kill microbes, they merely assist to get them killed

Vaccination

• One method of obtaining memory against a specific epitope is to Vaccinate