Immunology in a Nutshell
- Innate Immunity – Rapid responses to a broad range of microbes
- Acquired Immunity – Slower responses to specific microbes
External Defence
(First line of defence)
|
Internal Defence
(Second line of defence)
|
Internal Defence
(Third line of defence)
|
Skin
|
Phagocytic cells
|
Humoral response (antibodies)
|
Mucosa membrane
|
Antimicrobial proteins
|
Cell-mediated response
|
Secretions
|
Natural killer cells
|
Cytotoxic lymphocytes
|
FIRST LINE OF DEFENSE: (Aim) Prevent
microorganisms from gaining access to the body.
There
are different types of natural barriers that prevent the entry of foreign
bodies inside. Some of the natural barriers include skin, mucosa membrane and
secretions as well.
SECOND LINE OF DEFENSE: (Aim) To recognize,
neutralize and destroy invaders.
The body's way of dealing with non-specific invasion
Acquired
Immunity: (Pathogen Specific):
1st
time attack – mild response by the body = Primary response
2nd
time attack – more intense response = Secondary response or ANAMNESTIC RESPONSE
Third line of defense: specific defense mechanisms
Q. How
do we deal with specific and recurring invasion?
Lymphocytes are pivotal cells
to deal with specific defence mechanisms. Primary and secondary responses are
carried out with the help of two specific lymphocytes – B lymphocytes and
T-lymphocytes.
§ B-lymphocytes produce an
array of protein in response to pathogens into our blood to fight with them.
These proteins are called ANTIBODIES.
Each antibody is a protein molecule called Immunoglobulin.
Antigens are usually glycoproteins.
Antigens are usually glycoproteins.
Q. Where they come from? Where do they live?
Q. How do we know that lymphocytes
are required for adaptive immunity?
Q. How do we indicate the
specific response and get the lymphocytes involved?
Foreign antigens are
presented for identification, but first we need to distinguish “self” from “foreign.”
Two classes of proteins:
- Class I MHC – present on all nucleated cells
- Class II MHC – present on macrophages, dendritic cells and B-cells
The macrophage represents
the antigen to the outside world that a foreign body has been recognized. The
MHC-antigen complex is first recognized by T-helper cells.
T-helper cells when meet
with APC, they get activated and secrete cytokines to stimulate B-cells to
produce antibodies. This complex is further supported by CD4 molecule.
Antigen recognition by T4
leads to a great activation process. In the meantime, any infected cell (eg.
Muscle cell) might be infected by the same bacterium.
The T-lymphocytes do not
secrete antibodies, but help B-cells produce them.
Each antibody consists of:
- 4 peptide chains –
- 2 small (light chain)
- 2 longer (heavy chain)
Hence, an antibody can be
represented as H2L2
Types of antibodies:
(NOTE: USE THE WORD MEGA-D
TO REMEMBER THEM)
- IgM = first antibody to be produced in the body in response to antigens 5 H2L2
- IgE = for allergy, 1 H2L2
- IgG = 80% of the serum antibodies 1 H2L2; can cross the placenta
- IgA = 2 H2L2
- IgD = 1 H2L2
Note: The yellowish fluid
secreted by mother during the initial days of lactation has abundant antibodies
(IgA) to protect the infant = PASSIVE IMMUNITY
ACTIVE IMMUNITY = antibodies
are produced in response to the antigen in the body (slow process).
PASSIVE IMMUNITY = Injection
of antibody to patients directly.
