Download Immunity - Yengage

Immunity
Is the resistance of the body against pathogenic agents
Types-- Natural (innate) immunity and
Acquired immunity
Natural/ innate/ nonspecific immunity
•It is present since birth, prevents entry of micro organisms into
the body.
•It is the first line of defense against any pathogens.
Mechanisms involved—
Phagocytic activity of WBCs
Acid in the stomach and the enzymes in GIT
Lysozymes present in the tears and saliva
Protective function of skin
Acquired immunity /specific immunity
If the invaders overcome the natural immune system, then
the acquired immune system comes into play.
It is the resistance developed against any specific foreign
body, so it is also known as specific immunity.
It’s the most powerful immune mechanism
Types– Cellular immunity by T lymphocytes and
Humoral immunity by B lymphocytes.
Development of acquired immune system
During the fetal development and neonatal life, some
lymphocyte precursors from the bone marrow enters the
thymus gland and becomes transformed into T-lymphocytes
and some precursors enter liver, spleen and bone marrow and
get transformed into B-lymphocytes
Schematic chart to show the role of T and B lymphocytes in immunity
Suppressor T cell
Thymosin a hormone secreted by thymus accelerates the
proliferation and activation of lymphocytes in thymus.
Types—Helper T cell or inducer T cell
Cytotoxic T cell or Killer Tcell
Suppressor T cell
Memory T cell
After transformation the T lymphocytes migrate and stay in
lymphoid tissues present in lymph nodes, spleen, bone
marrow and GIT .
B-Lymphocytes were first discovered in “bursa fabricius” in
birds
They are transformed into two types
Plasma cells and
Memory cells
After transformation they migrate and stay in lymphoid
tissue.
Plasma cells forms and secrete protein Immunoglobulins
IgG, IgA, IgM, IgD and IgE
Development of cell mediated immunity
It develops when an antigen from the invading micro organism
is exposed to the T-lymphocytes.
The exposure or presentation of antigen to the lymphocytes is
done by-Macrophages
B lymphocytes and
Dendritic cells
The antigenic products activate the helper T cells and Blymphocytes
The macrophages also secrete interleukin-1, which brings
about activation and proliferation of lymphocytes
Helper T cell—
Promotes various activities of immune system; it
stimulates other T cells and B cells.
Two types of helper T cellsTH1—secretes IL2 and gamma-interferon concerned with
cellular immunity.
TH2—secretes IL4 and IL5 concerned with humoral
immunity.
Cytotoxic T cell—
The activated T cells comes into circulation to destroy the
invading organism
Mechanism of action– The membrane of cytotoxic T cells
contain receptor protein to which the antigens or organisms
tightly bind with. The organism is destroyed due to release
of cytotoxic substances from the T cell.
The cytotoxic T cells can also destroy—
Cancer cells,
transplanted cells
tissues affected by foreign bodies.
Suppressor T cells—
Suppresses the activities of cytotoxic T cells and prevents it
from destroying the body’s own tissue.
It also suppresses helper T cells.
Memory T cell—
Some of the activated T cells do not enter the circulation
but migrate to various lymphoid tissue, and get activated
when body is exposed to the same antigen again.
The response is immediate and more powerful.
Specificity of T cells—Each T cell gets activated by only one
type of antigen.
Development of humoral immunity
• Is the major defensive mechanism against bacterial
infection
• The antigen of the invading organism is presented to B
lymphocytes to activate them and also helper T cells.
•The B lymphocytes proliferate and transform into memory
B cells and “plasma cells”.
•The plasma cells secrete large quantity of antibodies
(about 2000 molecules per second)
•Antibodies are produced till the end of lifespan of plasma
cell (several days to weeks).
Memory B cells
The memory B cells remain inactive until the body is
exposed to same antigen for the second time.
The antibodies produced on first exposure is less in
concentration, takes longer time for production and belong to
IgM type.
On second exposure, the antibody produced is faster,
more in concentration and belongs to IgG type.
This forms the basic principle of vaccination against
infection.
Graph showing primary and secondary immune
responses
Immunization process
Cellular and humoral immunity differences
Cellular
Humoral
Is by T lymphocyte
Is by B lymphocyte
Cells are processed in thymus
Cells are processed in lymph
nodes, liver and spleen
Exposure to antigen produces
helper, suppressor, memory and
cytotoxic cells
Exposure to antigen produces
plasma and memory cells
Lymphocytes burr holes in the cells Plasma cells synthesize and release
to be destroyed by releasing
free antibodies in to circulation
substances like interlukin,
prostaglandin etc.
Cellular and humoral immunity differences continued
T lymphocytes
B lymphocytes
80% of circulating lymphocytes
belong to this group
Only 20% circulating lymphocytes
belong to this group.
Have role in responses against
bacteria, fungi, viruses and also
against transplanted organs and
tissues.
Have role against bacteria only.
Antibodies / Immunoglobulins
• Produced by B lymphocytes, are gamma globulin
fraction of plasma, form 20% of plasma proteins.
Structure of immunoglobulin
Mechanism of action of antibodies—
Direct action– agglutination
precipitation
neutralization
lysis
Action of antibody through complement system
This action is stronger than direct action, as the
complement system accelerates the fight against invading
organism.
Complement system involves plasma enzymes named C1
to C9. C1 has 3 subunits C1q, C1r, C1s.
These enzymes are in inactive form and get activated by 2
ways---Classical pathway and
Alternate pathway.
Classical pathway—
C1 binds with the antibodies and triggers a series of
events to activate other enzymes. The enzymes produce
following activities—
Opsonization
Lysis
Chemotaxis
Agglutination
Neutralization
Activation of basophils.
Alternate pathway—
Activation of alternate pathway is triggered due to
binding of a protein present in the circulation “factor1” with
the polysaccharide present on the cell membrane of
invading organism.
This activates C3 and C5 which ultimately attack the
organism.
Immunization
Is done by subjecting the individual to an antigen to induce the
immune resistance of the body, to fight against a specific
disease.
Passive immunity– No challenging of immune system of the
body. Done by administration of serum or gamma globulins
from a person who is already immunized
Passive natural– maternal antibodies
Passive artificial– injecting antibodies from other sources
Active immunity—immunization is acquired by activating the
immune system.
Active natural—infection
Active artificial—vaccines, toxoids
Types of immunity
Immune deficiency diseases—
Due to defective component of immune system
Types—Congenital immune deficiency disease
eg-Di George’s syndrome
Acquired immune deficiency disease (AIDS)
Autoimmune diseases—
IDDM
Myasthenia gravis
Rheumatoid arthritis