Module 11: Specific Defence Mechanism of the Host Flashcards
Specific Immunity - Third Line of Defence
activated when host physical barriers and second line mechanisms fail to control infectious agent
Antigen/Immunogen
molecule which stimulates a response by B and T cells
Epitope
B and T cells recognize and respond to only a portion of the antigen molecule
Hapten
incomplete or partial antigen, cannot illicit an immune response by itself
The Major Histocompatibility Complex (MHC)
set of genes which produce molecules on cells which are important in recognizing what is “self”
MHC Class 1 Molecules
found on nucleated cells, allow recognition of self
MHC Class 2 Molecules
found on macrophages, dendritic cells and B cells
Lymphocyte Maturation
- B-cells mature in the bone marrow
- T-cells mature in the thymus
- both migrate to the lymphoid organs (spleen and lymph nodes)
T-Cell Maturation
- directed by thymus gland and its hormones
- Co-receptors CDS: help in binding
- CD4: T-helper cells, bind to MHC II
- CD8: cytotoxic T cells, bind to MHC I
B-Cell Maturation
- directed by stroll cells in the bone marrow
- B-Cell receptors = immunoglobulins
- MHC II on surface
Immunologic Diversity
- by the time T and B cells reach the lymphoid tissues each one is already equipped to respond to a single antigen
- extensive gene rearrangement of more than 500 gene segments
Antigen Presentation
- Antigen present cell (APC) = macrophage, dendritic cell (B-cell)
- macrophage engulfs pathogen and it is digested into “pieces”
- “pieces” are antigen which bind to MHC II molecules
- antigen is presented and T-cell binds
Clonal Selection
correct T-cell or B-cell binds to antigen
Clonal Expansion
replication of the correct T or B cells
T-Cell Activation
- activated T-cells go on to differentiate into different types of T-cells with specific function or become memory T-cell
- cell mediated immunity
Helper T-cells
- critical in regulating immune reactions to antigens
- involved in activating macrophages, B-cells and cytotoxic T-cells
- most abundant
Regulatory T-cells
- controls T-cell response
Cytotoxic T-cells
- destroy infected host cells
- attack any abnormal cells they encounter
Memory T-cells
- mount an immune response upon subsequent contact
- long lasting
B-cell Activation
- B-cell receptors are called immunoglobulins
- most B-cells are activated by interacting with an activated T-helper cell
- once activated, B-cells differentiate into plasma cells regulating B cells or memory B-cells
- plasma cells secrete antibodies
- humeral immunity
Antibody (Immunoglobulin) Structure
- two fragments
- polypeptide chains
- the end of each fab fragment folds into a groove that will accommodate one epitope
Principal activity of antibody
- untie, immobilize, call attention to or neutralize the antigen to which it is bound
- coat the surface of bacterium preventing its normal function
Neutralization
- antibodies fill the surface receptors on a virus or active site microbial enzyme to prevent it form attaching
Opsonization
- makes microbes more recognizable by phagocytes
Agglutination
- antibodies link cells into large clumps, renders microbes immobilizes and enhances their phagocytosis
Antigen - Antibody Interactions
interaction with complement proteins can result in rupture of cells
Antitoxin
special type of antibody that neutralizes bacterial toxins
Serology
- in vitro diagnostic testing of serum
- detection of antibodies/antigens in the serum
Antibody titre
concentration of antibodies
Immunity
an acquired resistance to an infectious agent due to prior contact with that agent
Four Types of Acquired Immunity
- can be natural or artificial
- can be active or passive
Natural Immunity
is acquired through normal life experiences of an individual and is not induced though medical means
Artificial Immunity
is protection produced through medial procedures
Active Immunity
- creates memory
- requires several days to develop
- long lasting
Passive Immunity
- individual receives immune substances that were produced in another human or animal donor
- lack of memory
- lack of new antibodies produced
- shot-term effectiveness
Natural Active Immunity
after recovering from infectious disease, antibodies are produced
Natural Passive Immunity
antibodies passed on from mother to child
Artificial Active Immunity
vaccines - trigger production of antibodies
Artificial Passive Immunity
- preparation that contains specific antibodies specific agent
- human serum
Vaccines
purpose is to stimulate a primary response and a memory response, so that if pathogen is encountered again, a secondary response occurs and will be much quicker
Characteristics of an Effective Vaccine
- should have low level side-effcts or toxicity
- should stimulate both B-cell and T-cell response
- should have long-term lasting effects
- should not require numerous does or boosters
Types of Vaccines
- whole cell vaccines: live, attenuated cells or viruses; killed cells or inactivated viruses
- subunit vaccines: subunits manufactured via genetic engineering
Adjuvants
- some vaccines require addition of a special binding substance
- any compound added to a vaccine to enhance the immune response
- allow antigen to remain present at injection site for longer periods of time
- can act as irritants to stimulate and amplify the immune response
Hypersensitivity
- over reactivity of the immune system
- tissues are attacked by immune factors which cannot distinguish what is self from non-self
- 4 types
Type 1 - Allergy
- exaggerated immune response that is manifested by inflammation
- sensitive to repeated contact with antigens called allergens
- two levels or severity
Atopy
chronic local allergy - hay fever, asthma
Anaphylaxis
systemic, sometimes fatal; involves airway obstruction and circulatory collapse
Type 2 - Antibody Mediated
- complement assisted destruction of foreign cells by antibodies directed against those cells’ surface antigens
- red blood cells, Rh factor
Type 3 - Immune Complex Mediated
- involves the reaction of soluble antigen with antibody, resulting complexes that are deposited in various tissues of the body
- when second exposure occurs, it reacts with antibodies to form antigen-antibody complexes
- antigen-antibody complexes are so abundant that they are deposited into the basement membrane of epithelia tissue
- neutrophils release granules which digest tissue and cause a destructive inflammatory condition
Arthus Reaction
acute response to a second injection of drugs or vaccines at the same site as the first injection
Serum Sickness
immune complexes enter circulation and deposited throughout the body
Type 4 - T-Cell Mediated
T-cells respond to antigens displayed on self tissues or transplanted foreign cells
