Download Human Defense - Faculty Sites

Human Defense
Levels of Defense – Your body can tell the difference between your cells
and those that are not yours.
Primary Line of Defense – chemical and mechanical methods to keep
microbes out of the body, nonspecific

Epidermis – sebum, perspiration, keratinized cells

Eyes – mucus covering, lacrimal apparatus, tears

Digestive system – saliva, mucus (goblet cells), HCl

Circulatory system – transferrins

Respiratory system – ciliary escalator

Urinary and reproductive systems – urine, vaginal secretions
1
Secondary Line of Defense – methods to control microbes once they
are in the body. Non specific

Phagocytosis – cell eating
o Method of action
1. Chemotaxis
2. Adherence
3. Ingestion
4. Digestion
5. Discharge

Inflammation caused by chemical signals given off by injured
tissues. Chemicals cause blood vessels to dilate, bringing more
white blood cells to the area.
o A local response to injury
o
Method of action
1. Chemotaxis
2. Vasodilation
3. Increased numbers of phagocytes
4. Clotting factors
5. Tissue repair

Fever – Leukocytes release chemicals which are carried to the
hypothalamus, increases body temperature and lowers the
amount of iron available in the blood.
o A systemic response to injury.
2

The complement system – numerous proteins in the blood that
act in an ordered sequence (or cascade) with each other and
bind onto and lyse foreign cells.
o Enhance phagocytosis and vasodilatation
o Can be activated in two ways –
1. Classical pathway – initiated by antigenantibody binding, to be covered later.
2. Alternative pathway – reaction does not involve
antibodies.
Results
 Complement proteins interact with cell
wall and form a membrane attack
complex (MAC) which forms a hole in
the cell surface.


Proteins coat bacterial cell making it
easier for phagocytosis.

Proteins stimulate mast cells and
basophils to produce histamine,
contributing to vasodilatation.
Interferon – an antiviral protein produced by viral infected cells.
Specific Defense – the Third Level of Defense
Recognition of specific foreign molecules called antigens, which results
in the host producing molecules designed specifically to attack that
antigen.

Antigen –
o
Examples –
o
Things that are not antigens -
3

Antibody –
o
Structure – Light and Heavy chains, variable and
constant regions, antigen binding sites
Five varieties
IgG
IgM
IgA
IgD
IgE
Function
%
Example
Results of Antigen – Antibody binding
 Agglutination – clumping
o Facilitates phagocytosis, IgM
4

Neutralization – antigens are inactivated
o Block antigen ability to attach to cell

Opsonization – antigen is coated, facilitate phagocytosis

Inflammation – IgG and IgM trigger complement system

Activation of complement system
Specific Defense
B cells and T cells
 B cells develop from stem cells
o Bone marrow, liver, yolk sac

Some B cells pass through thymus gland and become T cells
B cells = Humoral immunity, Antibody mediated immunity
 B cell lymphocytes contain antibodies on their cell membrane

Develop into
o Plasma cells = in the presence of antigen they clone
themselves and clones produce large amounts of
antibody
o
Memory cells = retain blueprint of antigen and rapidly
divide into plasma cells when antigen reappears

Primary response is slow

Secondary response is much faster, stronger
5
Monoclonal Antibodies – specific antibody produced in vitro by a B cell
clone which has been hybridized with a cancer cell.
 Used as a diagnostic tool
 Examples
T cells = Cell mediated Immunity
 T cells are not directly stimulated by the antigen

Antigens must be “presented” to T cell by macrophage
o Activated T cell functions
 Activate B cells – divide into plasma and
memory cells

Activate Cytotoxic T cells – produce enzyme
that breaks down plasma membrane of cells
infected by viruses

Activate more T cells (Helper)
6
Immunity – the ability to initiate defense against an antigen before it
causes illness.

Active – plasma and memory cells are present – long term

Passive – plasma but not memory cells are present – short term

Naturally acquired

Artificially acquired
7
Naturally Acquired Active Immunity
Naturally Acquired Passive Immunity
Artificially Acquired Active Immunity
Naturally Acquired Active Immunity
Vaccine Preparation
 Virus injected into fertilized chicken egg
 Virus reproduces
 Egg injected with weak formaldehyde solution
 Virus extracted, vaccine solution produced
Types of Vaccines
Attenuated Whole Agent Vaccine
Inactivated Whole Agent Vaccine
Toxoids
Subunit Vaccine
Conjugated Vaccine
Nucleic Acid Vaccine
8