Adaptive Immunity: Chapter 16

• Chapter 16 discusses Adaptive Immunity

Overview of Adaptive Immunity

• Adaptive immunity aids in recognizing and defending the body against specific invaders and their products
• Adaptive immunity is not functional at birth
• Adaptive immunity attributes include:
  • Specificity due to recognition of unique antigens
  • Memory to the same antigens

Lymphocytes

• Adaptive immunity activities includes Lymphocytes
• The two main types of lymphocytes are B and T lymphocytes

B Lymphocytes

• Humoral Immunity: Targets attacking invaders outside of cells, specifically in the blood
• Target extracellular pathogens/toxins

T Lymphocytes

• Cell Mediated Immunity: Targets attacking infected cells inside the cells, kills cells that are already infected
• Targets intracellular pathogens

Antigens

• Both T and B cells require recognition of Antigens
• Antigens are molecules (surface protein, carb, lipid) the body recognizes as foreign and worthy of attack
• Primarily
• Three basic types:
  • Exogenous antigens are found outside a body's cells, including toxins, microbial cell walls, membranes, flagella, and pili.
  • Endogenous antigens are produced by microbes that reproduce inside a body's cells (replicating)
  • Autoantigens are self-made antigens been made by our DNA

Epitopes

• Antigens are recognized by three-dimensional regions called epitopes

Elements of Adaptive Immunity

• Epitopes are recognized by the lymphocytes when displayed as Major Histocompatibility Complexes (MHC)
• Major histocompatibility complexes are glycoproteins found in the membranes of most cells
• MHC and position epitopes for presentation to immune cells
• A cell that presents the antigen to the lymphocytes is called an Antigen Presenting Cell (APC)

MHC Proteins

• Two types of MHC proteins
  • MHC I is present on all nucleated cells, with the exception of red blood cells
  • MHC II is present on antigen presenting cells (APCs)
    • Wandering types: Macrophages, dendritic cells, and B cells

Antigen Processing

• Autoantigens are displayed as self MHC's
• Endogenous and exogenous antigens are processed into MHC proteins to display the pathogen epitopes
• MHC I is present if a nucleated cell (fixed)
• MHC I and MHC II are present if an antigen presenting cell (APC)

Lymphocyte Recognition

• T and B cells are able to recognize the pathogen displayed MHC's
• T cells have a T Cell Receptor (TCR) protein unique for each pathogen epitope
• A matching TCR exists for every possible epitope a person may contact
• B cells have B Cell Receptors (BCR) unique to pathogen epitopes (once again for all possible epitopes)
• Divisions of T and B cells occurs once recognition happens

Antigen Presenting Cell (APC) Recognition

• Recognition usually requires an Antigen Presenting Cell (APC)
• Examples: Macrophage, B cell, Dendritic Cell
• Interaction between T/B and APC is required to multiply the number of T/B cells
• This interaction is called Costimulation
• Costimulation results from surface molecules on each cell and release of Cytokines

Immune Response Cytokines

• Interleukins (ILs) signal among leukocytes
• Interferons (IFNs) are antiviral proteins that may act as cytokines
• Growth factors are proteins that stimulate stem cells to divide
• Tumor necrosis factor (TNF) is secreted by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation

Production of T/B Cells

• Recognition and costimulation leads to a mass production of T/B cells to attack the foreign epitopes

T Cell Activation

• Cell mediated-attack of infected cells
• Cytotoxic T lymphocyte (T8, Tc): Facilitates the attacking and killing
  • Directly kills other cells with perforins, punch holes in the cell
• Helper T lymphocyte (T4, Th): Helps make the army
  • Helps multiply B cells and cytotoxic T cells
  • Includes type 1 (Th1) and type 2 (Th2)
• Memory T lymphocytes
  • Remember same epitope in the future, B cells will use the future
• Regulatory T lymphocyte inhibits autoantigen attack
  • Prevents self attack for auto immune diseases

Cell-Mediated Immune Response

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

B Cell Activation

• Humoral Immunity: attacking in the blood before getting into cells
• Production of ANTIBODIES to attack extracellular epitopes
• Lymphocyte types:
  • B lymphocytes
    • Initially recognizes foreign epitopes; act as APC
    • Becomes plasma cells
  • Plasma cells produce antibodies
  • Helper T lymphocytes (T4, Th)
    • Helps multiply B cells and cytotoxic T cells
    • Includes type 1 (Th1) and type 2 (Th2) using these cells now
  • Memory B lymphocytes
    • Remembers same epitope in the future
    • Allows us to not get the same infection again

Important B-Cells Points

• 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

Antibody Properties

• Basic Structure
  • Two heavy chains, two light chains
  • Each chain has a variable region that creates an Antigen Binding Site
  • A site is epitope specific
  • The stem of the heavy chains leads to different types of antibodies

Types of Antibodies

• IgM is the first antibody produced (acute)
• IgG is the most common and longest-lasting (chronic)
• IgA associated with body secretions (mucous membrane)
• IgE is involved in response to parasitic infections and allergies
• The exact function of IgD is unknown
• IG = immunoglobulin

Antibodies

• Antibodies have a specific effect
  • Phagocytosis
  • Lysis
  • Agglutination (clumping); attaches microbes together
  • Neutralize
• Antibodies do not kill microbes; they assist to get them killed

Gaining Memory

• Obtaining memory against a specific epitope is to Vaccinate