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Immunology
Organs of immune system
Lymphatic system is a part of the circulatory system composed of lymphatic vessels that
transport fluid called lymph. Lymph is fluid that is formed when interstitial fluid enters in
the lymphatic vesseles of lymphatic system.
The lymphoid tissue can be primary and secondary depending of the stages of
lymphocyte development.
Primary lymphoid organs (p.l.t.) are organs where differentiation, proliferation and
maturation of pleuripotent stem cells into immune competent cells take place. Thymus
and bone marrow are p.l.t. involved in production of early lymphocytes.
Secondary lymphoid tissue (s.l.t.) maintains mature lymphocytes and initiates an
adaptive immune response. It is maintained by lymphoid nodes, lymphoid follicles in the
tonsils, spleen, etc.
Bonne marrow is a flexible tissue founded inner, hollow spaces of the flat bones and
long bones of the skeleton. All blood cells come from what are called stem cells within
the bone marrow. It is in the marrow that the various white blood cells of the immune
system form and migrate out into the circulation. In adults weighing about 65kg, b.m.
accounts approximately 2, 5 kg. B. m. is component of lymphatic system producing the
lymphocyte support the body’s immune system.
Thymus is located under thyroid gland in the chest cavity. It is large accumulation of
lymphoid tissue and it is involved in maturation T-cells. T-cells are those that mature in
thymus. As the immune system becoming mature the thymus becoming smaller and
smaller. In the adult will be much smaller than in young individual.
Lymph nodes- afferent vessels take lymph into the node, efferent will send lymph out of
the node. As the lymph travel trough lymph nodes if there are any microorganisms,
bacteria, viruses, lymphocyte will recognize them and they will include body in attack
against this pathogens. Lymph nodes get swollen due to accumulation these pathogens,
because they are doing their job. So if the lymphocyte is swollen, it tells us that there is
an infection.
Tonsils protect entrance of respiratory system. Why are they in this position? Since you
are much more likely to bring something foreigner into your body from mouth. They are
here to protect your body against that. When they swollen they can hurt person and effect
the ability of breathing.
Spleen is organ located directly beneath the diaphragm. It is approximately about 200g in
weight. Spleen is involved in recycling blood cells, storage the iron from recycled red
blood cells, storage of blood as a reserve in the event of any shortage and in production of
lymphocyte.
The mono nuclear phagocyte system is part of immune system that consists of phagocyte
cells located in reticular connective tissue. It consists of Kuppfer cells of liver and
reticular cells of red bone marrow. This system defense body against foreign substances
by initiation antibody release and phagocytosis.Than they phagocytes the invading
microorganisms. The stem cells of bone marrow are involved in the production of
lymphocytes.
Acquisition of immunity (types of immunity)
1. Active immunity, the individual alone produces antibodies against antigens.
Sometimes develops naturally after a person is infected with pathogen, or person
can artificially immunize against the pathogens.
2. Passive immunity, the individual is given prepared antibodies; they are not
produced by the individual B lymphocytes.
Types of immunity
Pathogens are the organisms that can damage your body, such as viruses, bacteria, fungi,
parasites.
The immune system on the first line defense keep this out and it they get into your body it
kill them and eliminate so that we don’t get sick.
The first line defense prevent microbe entering the body:
Skin: is mechanical barrier, protect from external harmful microorganisms.
Tears and sweat have a high salt concentration, eliminate some bacteria. Mucous
membranes are tissues that line body cavities or canals such as the nose, mouth, urethra,
and rectum. Mucous membranes produce thick, slippery liquid called mucus that protects
the membranes and keeps them moist. Microbes ingested in food are destroyed in the
stomach by gastric juices which include HCl and enzymes.
But, sometimes these foreign substances get into our body and we need second line
defense.
Inflammatory response: After an infection when you see blood flowing to certain part of
your body and you see there is an infection that means it is blood bringing cells that can
fight against type infection that you have. It’s just bringing fluid to fight. Phagocytes are
class of cell that eats up of pathogens because it is nonspecific; it has receptors that
response to thing that is known as bad. When phagocytes “see” foreign bacteria it
contacts with them and this triggers phagocyte to engulf. It will wrap around the bacteria.
Once time when bacteria find themselves inside phagocyte cells…there are some
organelles that we call lysosomes. This little package will merge with bacteria and will
dups. his contents into this pathogen and destroy it up.
This is nonspecific immunity. It is called non-specific because they don’t respond on
certain type of viruses they respond to everything what is foreign. In nonspecific
immunity body also use the certain chemicals called interferon. Interferon is joust a
protein which is produced by host organisms in response to infections. They function is
deactivate viruses.
Today is possible interferon production in the pharmaceutical industry. The gene
responsible for production of interferon is placed into the genome of bacteria.
Why bacteria? Because, bacteria do not have a nucleus.
They have a single circular DNA and chromosome does not have to think on which
side of cell they will go. So the rate of bacteria fission is rapid, large amounts of
interferon may be synthesized in a short period of time.
Specific immunity. T and B lymphocytes have main responsibility in non-specific
immunity. B lymphocytes develop in the bone marrow (B) and they participate in
humoral response. T- Lymphocytes they develop in thymus (T) and participate in cell
mediate response.
What is the difference between each other? If I get infected by viruses and when viruses
floating around in my system that means the virus is in the area of humoral response take
place. If these viruses infiltrate cells then we can talk about cell mediate response.
1. Humoral response: B lymphocyte comes from bone marrow. It has all these
proteins on surface. These proteins are called antibodies and they are
immunoglobulin (Ig). There are five types of immunoglobulin IgA, IgM, IgG,
IgE, IgD. Antibody is V in shaped which sit on surface B cells. Ig is made up of
four chain, two light chain (they are called light because they are smaller) and two
heavy chains (the bigger one). And these give antibody V shape. There is some
very important region in heavy and light chain. The most important regions are at
the end of the light and heavy chain. It is called variable region. That gives
antibody specify for antigen. The rest is constant region. One B cells produce one
type antibodies. This is very important because you have different antibody for
specific pathogen, ex. if you are is attacked by pathogen 1, and the antibody B cell
No1 will stick on the surface the pathogen1. Those of the B cell No2 do not stick.
Now if there is second pathogen No2, antibodies B cell No2 stick on this
pathogen. So you have different B cell for different pathogen. B lymphocytes
secrete antibody into blood stream.
How does B lymphocyte get activated and how do they turn into memory B cell and
plasma B cell?
T cells react to a foreign antigen and they stimulated B cells to divide. Once time when
this cell gets activated it is going to start cloning itself. Multiple versions of these and
they start differentiate; they start to take particular role. They differentiate into memory
cells. Memory cells stay long time with receptor on them and they will provide secondary
immune response when the same antigen enters in body again. And some cells
differentiate in plasma B cells. Plasma B cells will produce 2000 antibodies per second,
and they will provide something what we call primary immune response it is joust first
reaction to a particular foreign antigen.
2. Cell mediate response: T cells mature in thymus and they are involved in cell
mediated immunity. There are several types of T lymphocytes and each one has a
distinct function. Cytotoxic T cells attack cells that have been infiltrated; they
attract cells that are abnormal. What does helper T cells do is kind of alarm
immune system; they produce chemicals and stimulate other immune cells.
Suppressor T cells suppress the immune response. Each of these cytotoxic or
helper T cell can become memory B cells which will remain in body to provide
long lasting immunity.