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The Immune Response
The Third Line of Defense
 The third line of defense involves a specific
response that is effective against specific pathogens.
 This involves a specialized group of white blood
cells called lymphocytes, which produce
antibodies.
 Antibodies are protein molecules that protect the body
from invaders.
The Third Line of Defense
(cont’d)
 All cells have special markers located on their cell
membranes, which are known as antigens
(antibody generator).
 Normally, the immune system does not react to the
body’s own markers.
 However, intruding cells or foreign proteins activate the
production of antibodies.
The Third Line of Defense
(cont’d)
 There are two different types of lymphocytes found
in the immune system.
 The first is the T cell, which is produced in the bone
marrow and is stored in a tiny organ called the thymus
gland.
 The T cell’s function is to seek out the intruder and
signal the attack.
 Acting much like a sentry, some T cells identify the
invader by its antigen markers.
The Third Line of Defense
(cont’d)
 Once the antigen is identified, another T cell passes
this information on to the antibody producing B cell.
 B cells multiply and produce chemical weapons:
the antibodies.
 Each B cell produces a single type of antibody.
Antigen-Antibody Reactions
 Antibodies are Y-shaped proteins that are produced
to target specific foreign invaders.
 Antibodies are specific; this means that an antibody
produced against the influenza virus is not effective
against HIV.
 Each antibody has a shape that is complementary to its
specific antigen.
Antigen-Antibody Reactions
(cont’d)
 There are many different antigen markers on the
membrane of a virus or bacterium.
 The attachment of antibodies to the antigens increases
the size of the complex, making the antigen-antibody
combination more conspicuous and, therefore, more
easily engulfed and destroyed by macrophages.
Immune Response
 Step 1: Pathogen enters body.
Immune Response (cont’d)
 Step 2: Macrophages engulf pathogen and pushes the
antigen markers to its outer membrane.
Immune Response (cont’d)
 Step 3: A helper T-cell identifies the antigen present on
the cell membrane of the macrophage.
Immune Response (cont’d)
 Step 4: Helper T cells alert the B cells, which multiply
and begin to produce antibodies.
Immune Response (cont’d)
 Step 5: Antibodies attach to the antigens.
Immune Response (cont’d)
 Step 6: Antibodies immobilize and tag invaders for
macrophages to destroy.
Immune Response (cont’d)
 Step 7: Helper T cells also send out chemicals to
stimulate killer T cells.
 Killer T cells puncture the cell membranes of intruders.
If killer T cells find a viral coat attached to a cell
membrane, the T cell attacks the infected cells.
Immune Response (cont’d)
 Step 8: During the immune response, memory B cells
and memory T cells are created. These cells contain a
blueprint of the invader’s antigen.
 This will allow the immune system to react faster the
next time that particular antigen enters the body.
Immune Response (cont’d)
 Step 9: A suppressor T cell ends the battle by signaling
the immune system to return to its pre-infection state.
Immune Response

Step 1: Pathogen enters the body.

Step 2: Macrophages engulf pathogen and pushes the antigen markers to its outer
membrane.

Step 3: A helper T-cell identifies the antigen present on the cell membrane of the
macrophage.

Step 4: Helper T cells alert the B cells, which multiply and begin to produce
antibodies.

Step 5: Antibodies attach to the antigens.

Step 6: Antibodies immobilize and tag invaders for macrophages to destroy.

Step 7: Helper T cells also send out chemicals to stimulate killer T cells.

Step 8: During the immune response, memory B cells and memory T cells are
created.

Step 9: A suppressor T cell ends the battle by signaling the immune system to
return to its pre-infection state.
Components of the Immune
Response
Components of the Immune
Response
Components of the Immune
Response