We need Specific
B cells and T cells accomplish this.
B cells are important for antibody induced immunity
in body fluids
T cells are important for cell based immunity.
(Think abnormal cells and pathogens in cells)
First let’s Review NonSpecific Defenses:
Phagocytes in blood and tissues
Fever and Inflammation
But it is not enough!
3 Cell Types of the
First line of defense, often attack and remove
microorganisms before lymphocytes (T cells and B
cells) detect them.
Microphages – patrol blood
Macrophages – patrol peripheral tissue
Specific Defense Cell 1: T cells
Thymus dependent cells, recognize antigens when bound to special
proteins in a cell membrane, called MHC proteins.
4 Types of T cells
Cytotoxic- highly mobile, seek out and destroy abnormal
or infected cells
Helper- activate B cells so they are able to produce
Suppressor- Keep the immune system from overreacting
Memory- on 2nd exposure automatically transform to cytotoxic
Specific Defense Cell 2: B cells
2 types of B cells
B cells - Bone marrow derived cells, each carries its own
specific antibody molecule that fits a corresponding
antigen. Needs the Helper T cells to activate and
stimulate their division. They will eventually divide into
plasma cells and Memory B cells.
B memory cells – on second exposure they divide into
plasma cells that secrete antibodies in massive
-When stimulated by cytokines from a T cell, plasma cells
can secrete up to 100 million antibody molecules an HOUR
T cell activation
When a macrophage (“think pac-man”)
engulfs a pathogen with an antigen on it, the
antigens are presented to the T-cell by placing them
on its cell membrane at the MHC.
The T-cell then is able to recognize and bind to the
antigen there and begin dividing.
B cell activation
On their surface B cells have specific antibodies that
bind with specific antigens.
B cells engulf the antigen and present it on their cell
membrane to be recognized by an activated Helper T
cell, which gives the B cell the “go ahead”.
The T-cell attaches to the part of the B cell membrane
where the antigen is and begins to secrete cytokines to
activate the B cell.
The B cell can now divide, accelerate plasma cell
formation, and enhance antibody production.
Remember the difference!
Antibodies do not peak
until 1-2 weeks after
Even low antigen
immediately trigger memory
B cell response.
IgM are first to appear, but
do not create memory
cells. Immediate, but
Antibodies increase rapidly
and reach much higher
concentrations than with the
Invading organism is often
destroyed before symptoms
IgG rises more slowly and
creates memory cells.
Takes over response.
Types of Antibodies
IgA – Found in secretions of the body.
IgD – Found on the cell membrane of B cells.
IgE – Found wherever IgA is. Thought to be involved
in triggering allergic reactions.
IgG – Primarily recognizes bacteria, viruses, and
IgM – a very large antibody that binds to food and
incompatible blood cells.
How Antibodies Attack
Phagocyte recognition and destruction
Antigens clump together and are targeted by
The toxic portion of the antigen is covered
Activate complement proteins that form holes in
So, how does the lymphatic system
fit into all of this?
It’s primary function is the production,
maintenance, and distribution of
Remember, those are the T cells and B cells essential for
Organs of the Lymphatic
The organs of the Lymphatic System include:
How does the Lymphatic
More fluid is delivered to tissues than can be
The Lymphatic System’s circulatory network
returns this fluid to the blood stream.
On the way to the major collecting ducts,
pathogens are filtered at stops such as the spleen
and lymph nodes
Lymphocytes, produced in the organs of the
lymphatic system, freely flow through this circuit
Formation of Lymphocytes
Two different types are produced in the bone
One type stays there, the other migrates to the
thymus to mature, separated from the blood.
When they have completed maturing they return
to the bone marrow and lymphoid tissues and
organs, such as the spleen.
All lymphoid organs are separated from the
surrounding tissues by a fibrous connective tissue
What is lymph?
A thin, watery fluid originating in organs and tissues
of the body.
It circulates through the lymphatic vessels and is
filtered by the lymph nodes.
It enters the blood stream at the junction of the
internal jugular and subclavian veins.
Flow of Lymph
Small Lymphatic Vessels
Superficial and Deep Lymphatics
Major Lymph Collecting Ducts
The Filtering Process
Lymph nodes – Purify lymph before it returns to the
venous circulation. 99% of the antigens are
A T cell may spend 20 hours in a lymph node.
A B cell may spend 30 hours in a lymph node.
Other organs of the
Thymus – the thymus provides a place for
lymphocytes to mature, separated from the
The thymus also produces several hormones that
are important to the development and
maintenance of a normal immune system.
Other Organs of the
Spleen – Has the largest collection of lymphoid
tissue in the body and does for blood what lymph
nodes do for lymph.
-removal of abnormal blood cells and
-storage of iron from recycled red blood cells
-initiation of immune response by B and T
in response to circulating antigens.
Diseases of Immunity
Human Immunodeficiency Virus
Pathology of HIV
Depletes Helper T cells
Circulating antibodies also decrease, and cell
mediated immunity is reduced. (As a result
pathogens that are usually harmless create
The surplus in suppressor T cells as Helper T cells die
turns off the normal immune response.
Immune surveillance is also decreased, increasing
Stages of HIV
Large amounts of the virus
are being reproduced in the
HIV reproduces at
low levels, but is still
Helper T cell count
falls to dangerously
Usually occurs within 2-4
weeks of infection
It is still possible to
transmit the virus
After rapid Helper T cell
destruction, immune system
kicks in and body returns to
a viral set point.
This period may last
8 years or longer.
At this stage the
immune system is
infections are likely.
Survival is typically 3
years with AIDS. It is
only 1 year with an
Surprising HIV Facts
Virus enters the body under clever camouflage,
cloaked in sugar molecules.
There are different strains of the virus, some more
deadly than others.
34 million people are living with HIV today.
Transmission to a fetus from the mother is now
considered entirely avoidable with medication.
A quarter of AIDS deaths are from TB
Innocent Kingsely Asogwa
Jefferey C. Pommerville