The document discusses the origin and functionality of immune cells, comparing T cells and B cells, and detailing their roles in the immune system. It also addresses the effects of aging on the immune response, highlighting diminished effectiveness, slower reactions, and increased risks of autoimmune diseases in older adults. Additionally, it explores ways to enhance immune function in the elderly through nutrition, exercise, and medical care.

1. Ida Sri Iswari
Unit Research and Development
Faculty of Medicine-Sanglah Hospital

3. Origin of immune cells
Origin of immune cells

4. Comparison of T cells and B cells
Comparison of T cells and B cells
Feature T cells B cells
Antigen receptors on surface Yes Yes
IgM on surface No Yes
CD3 proteins on surface Yes No
Clonal exansion after contact with specific antigen Yes Yes
Immnunoglobulin synthesis No Yes
Helper/suppressor regulator of antibody synthesis Yes No
IL-2, IL-4, IL-5 synthesis Yes No
Mediator of cellular immunity and delayed
hypersensitivity
Yes No
Maturation in thymus Yes No
Maturation in bursa o its equivalent No Yes

5. Interaction and functions of the immune system
Interaction and functions of the immune system

6. Introduction
Introduction
 Function of immune system is to prevent or
limit infections
 Protection provided by the cell-mediated
(T-cell) and antibody mediated (humoral/
B-cell)
 Functions of cell mediated immunity is
directed primarily against organism (fungi,
parasite, intracellular bacteria, virus and
tumor cells
 Functions of antibodies are :
1. neutralize toxin and viruses
2. to opsonize bacteria

7. Mayor functions of T cells and B cells
Mayor functions of T cells and B cells
Antibody – mediated
immunity (B cells)
Cell- mediated immunity
(T cells)
1. Host defence
against
infection (opsonize
bacteria, neutralize
toxins and viruses)
2. Allergy, eg Hay
fever
3. Autoimmunity
1. Host defence against
infection (M.tb, viruses,
and fungi)
2. Allergy, eg poison oak
3. Graft ang tumor
rejection
4. Regulation of antibody
response (help and
suppression)

8. T cells
T cells
To be devided into 2 main category :
1. regulatory
(helper, produce interleukins, supressor)
2. effector
cytotoxic
CD8  kill virus infected cells, tumor cells,
and allograft
CD4  delayed hypersensitivity against
intracellular organisms

9. Types of T cells
Types of T cells
 CD4, CD8 lymphocytes
 Activation of T cells (class II MHC,
IL-1, IL-2)
 T cell receptor (CD3 protein)
 Effect of superantigens on T cells

10. B cells
B cells
 Macrophages
 Natural kille cells
 Polymorphonuclear neutrophils
 Important cytokines

11. Antibodies
Antibodies
 Immunoglobulin structure (light
chain, heavy chain)
 Immunoglobulin classes (IgG,
IgA, IgM, IgD, IgE)
 Types (iso, allo, idiotypes)
 Immunoglobulin genes

13. Aging and the Immune System
Aging and the Immune System
As the human body enters its senior years,
its
 ability to fight off infection and other
health problems diminishes
significantly.
 immune system does not function as
efficiently in older adults as in younger
people.
 innate response to infection is not always
automatic in elderly people.
Burns EA, 2001.

14.  more than 20% of adults over age 65 who
have serious bacterial infections do not
have fevers.
 still has the ability to generate fevers and
other immunity weapons, but the central
nervous system is simply less sensitive to
immune signals and doesn't react as
quickly or efficiently to infection.

15.  Lymphocytes, which are cells produced in
the lymph glands, are essential to fight
infection.
 number of lymphocytes does not change
greatly in old age, but the configuration
of lymphocytes and their reaction to
infection does.
 elderly adults are less capable of
producing lymphocytes to combat
challenges to the immune system.

16.  The infection-fighting cells are less vigorous
and less effective
 the duration of antibody their response is
shorter and fewer cells are produced
 the immune system -- including lymphocytes
and other types of cells -- typically reacts
weakly and more slowly to infection
 elderly adults after age 70, are more likely to
produce autoantibodies, which attack parts of
the body itself instead of infections.
Autoantibodies are factors in causing
rheumatoid arthritis and atherosclerosis
(hardening of the arteries).

17. Improving the Immune System Response
Improving the Immune System Response
As the human body grows old, so does its
organs.
 The organs are less efficient
eg. Thymus, secretes important hormones,
particularly during puberty.
 elderly people, however, it is largely dormant.
 older adult lymphocytes exposed to thymic
hormones, the immune system is enhanced at
least temporarily.
 the secretion of hormones, including growth
hormone and melatonin, decline in old age and
may be related to a compromised immune
system.

18.  Soal ujian
 Imune stm yg spesifik apa dan nonspesifik apa
 Sebutkan beda sel b dan sel t perbedaan
persamaan

19.  prostaglandins, hormone-like acids that affect
important may increase in old age and inhibit
important immune cells from doing their jobs.
may also be more sensitive to the action of
prostaglandins could be a major cause of immune
deficiency
 Prostaglandins are produced by most tissues in the
body, but the immune system responds better in
older adults when prostaglandin production is
suppressed.
 Nutrition also plays a factor in a healthy immune
system. In both healthy and nutritionally deficient
older adults, vitamin and dietary supplements have
been found to enhance the response of the immune
system, resulting in fewer days of infectious
illnesses.

20.  Older adults often experience loss and stress,
and suppressed immunity has been associated
with bereavement, depression and poor social
support.
Maintaining an active social life and receiving
treatment for depression could boost the older
adult's immune system.
 It has not been proven that a less effective
immune system necessarily means more
infections or a shorter life.
However, in general, older adults experience
more infections and a greater severity of
infections than younger adults.

21.  In addition, older adults display a decreased
response to vaccines, including that for
streptococcal pneumonia, influenza (the flu)
more than 80% of the deaths related to
epidemics.
 Tetanus is another concern, since more than
70% of people over age 70 never received the
necessary tetanus vaccinations
While vaccines do not work as well in the
immune system of older adults, vaccinations
for diseases such as influenza, pneumonia,
hepatitis B, tuberculosis, diphtheria and
tetanus have been found to reduce mortality in
the elderly and are still worthwhile.

22. The Immune System and Aging
The Immune System and Aging
 HIV affects each of us differently.
Some people progress to symptoms very
quickly;
others live for 20-plus years without any
signs of immune suppression or symptoms.
 The immune system is greatly affected by
aging.
 Therefore, HIV infection -- coupled with
aging -- creates added challenges for
maintaining good health.

23. • Our immune system's ability to perform
declines with age.
• These changes happen at all levels, from
chemical changes in how our cells
communicate with one another to changes
in immune organs altogether.
• A study is currently underway on the
effects of HIV, aging and the immune
system.

24. The Skin
The Skin
 Skin is the first line of defense against
many infections. For many people, visible
signs of skin aging begins at about 25
years -- fine lines and wrinkles start to
reveal the natural process of the skin
breaking down.
 Then, as women enter menopause, the
fatty underlayer of skin thins from
hormonal changes. The skin also becomes
more vulnerable to cuts and abrasions, and
it loses some of its resilience and elasticity.

25. • Most skin conditions associated with aging
are relatively harmless and to some degree
unavoidable.
Others can be painful, itchy or even life-
threatening, like cancer.
Some include wrinkles, shingles, drying of
the skin, skin lesions (from warts to liver
spots), dermatitis, varicose veins and leg
ulcers.
• HIV affects the skin as well.
Often, skin conditions are among the first
signs of immune dysfunction associated
with HIV

26. The Thymus
The Thymus
 This organ is located beneath the
breastbone and above the heart.
 When we're born, the thymus is large,
nearly covering the whole chest like a bib.
 The organ is important for developing new
T-cells (naïve T-cells), including CD4+ and
CD8+ cells.

27. • In children this organ is very active, making many
new T-cells and building the immune defenses
that will help protect us late into our lives.
• In our early teens, the thymus has done most of
its job.
• We're then generally considered to be
immunologically adult.
in our early twenties, the thymus shrinks in size,
becomes fatty and is believed to contribute little to
new T-cells for the rest of our lives.
• Thus, a healthy, HIV-negative 40-year-old is not
likely to have much functioning thymus tissue.

28. • That people living with HIV are more likely to
have a functioning thymus than HIV-negative
people.
This might be because the immune system is
weakened and the thymus needs to re-grow in
response to immune suppression.
• Even still, a 40-year-old with HIV is less likely to
have robust thymus activity compared to a 20-
year-old with HIV.
Because this organ is so important for new T-cell
development, how aging impacts the potential for
immune reconstitution in HIV disease might be quite
profound.

29. The New or Naive T-cell
The New or Naive T-cell
 Naive T-cells are cells that can create an
immune response and deal with new
infections.
 The elderly have virtually no naïve T-cells.
 As you age, your immune system finds it
difficult and sometimes impossible to
respond to new infections like a young
person would. Your immune system may
take much longer to tackle an infection or it
may simply not respond at all.

30. Interleukin-2 (IL-2)
Interleukin-2 (IL-2)
 As we age, calcium gets depleted from our
bodies.
 Calcium is important for strong bones.
It also helps cells produce chemicals called
cytokines -- what your immune system
uses to communicate.
 IL-2 is one cytokine that is very important
for T-cell reproduction and their long-term
growth.

31. • As T-cells age, they lose the ability to
function properly and produce IL-2.
• As a person ages, there are changes in
their T-cell function and, as individual cells
age, there are changes in those cells'
function as well.
• HIV infection also decreases IL-2
production and T-cell dysfunction is well
documented in HIV disease

32. Telomere Length
Telomere Length
(end of a chromosome)
(end of a chromosome)
 With new technology, scientists can
measure a telomere and estimate the
replicative history of a cell. In 100-year-old
people, the telomere length inside their
cells is very short.
 Some studies show that the telomere
length in cells from people with HIV is
almost identical to those of a 100-year-old.
This suggests that HIV hastens the aging of
the immune system.

33. Other
Other Cells
Cells
 Aging impacts other cells as well, including
B-cells, which are important for making
antibodies.
Studies suggest that antibodies in elderly
people are limited, not able to deal with a
broad range of infections.
 Auto-antibodies have been correlated with
aging.
They are more prevalent in elderly people
and are associated with auto-immune
diseases, like arthritis or skin conditions.
Increased rates of auto-immune diseases
are also associated with HIV infection.

34.  Moreover, the development of antibodies in
response to vaccinations is markedly
reduced in both HIV-positive people and the
elderly.
 In the face of aging and HIV infection, there are
many ways to enhance and strengthen your
immune system.
 One way to strengthen your body and its ability to
fight disease is to work closely with a healthcare
professional to find out what's best for you.
 Other ways include basic skin care, improving
nutrition, getting age-appropriate health screening,
promptly treating conditions when they occur and
developing comprehensive preventive strategies

35. The immune system and aging
The immune system and aging
 The immune system changes throughout
life.
 At birth, specific immunity is not fully
developed.
 However, newborns have some antibodies,
which crossed the placenta from the mother
during pregnancy.
These antibodies protect newborns against
infections until their own immune system fully
develops. Breastfed newborns also receive
antibodies from the mother in the breast milk.

36. • As people age, the immune system becomes
less effective.
It becomes less able to distinguish self from
nonself.
• As a result, autoimmune disorders become more
common.
• Macrophages destroy bacteria, cancer cells, and
other antigens more slowly.
This slowdown may be one reason that cancer is
more common among older people.
• T lymphocytes respond less quickly to
antigens, and there are fewer lymphocytes
capable of responding to new antigens.
The body is less able to recognize and
defend against it.

37.  Older people have smaller amounts of
complement proteins than younger people,
especially during bacterial infections.
 These changes may partly explain why
pneumonia, influenza, infectious endocarditis,
and tetanus are more common among older
people and result in death more often.
 Also, vaccines are less likely to produce
immunity in older people.
 These changes in immune function may
contribute to the greater susceptibility of older
people to some infections and cancers.

38.  Nonspecific immunity is so named
because its components treat all foreign
substances in much the same way.
 The white blood cells involved in
nonspecific immunity are monocytes
(which develop into macrophages),
neutrophils, eosinophils, basophils, and
natural killer cells.
Each type has a slightly different
function.
The complement system and cytokines
also participate in nonspecific immunity.

39. Macrophages
Macrophages
 Macrophages develop from a type of white
blood cell called monocytes after monocytes
move from the bloodstream to the tissues.
 When infection occurs, monocytes leave the
bloodstream and move into the tissues.
 There, over a period of about 8 hours,
monocytes enlarge greatly and produce
granules within themselves.
 The granules are filled with enzymes and other
substances that help digest bacteria and other
foreign cells.
 Monocytes that have enlarged and contain
granules are macrophages. Macrophages stay
in the tissues.
 They ingest bacteria, foreign cells, and
damaged and dead cells. (The process of a cell
ingesting a microorganism, another cell, or cell
fragments is called phagocytosis, and cells that
ingest are called phagocytes.)

40. Neutrophils
Neutrophils
 Neutrophils ingest bacteria and other foreign
cells.
 Neutrophils contain granules that release
enzymes to help kill and digest these cells.
 Neutrophils circulate in the bloodstream and
must be signaled to leave the bloodstream
and enter tissues.
 The signal often comes from the bacteria
themselves, from complement proteins, or
from macrophages, all of which produce
substances that attract neutrophils to a
trouble spot. (The process of attracting cells
is called chemotaxis.)

41. Eosinophils
Eosinophils
 Eosinophils can ingest bacteria and other
foreign cells, contain granules filled with
enzymes to digest the ingested bacteria and
cells, and circulate in the bloodstream
 However, they are less active against
bacteria than are neutrophils and
macrophages.
 Their main function may be to attach to and
thus help immobilize and kill parasites.
 Eosinophils also participate in allergic
reactions (such as asthma

42. Basophils
Basophils
 Basophils do not ingest foreign cells.
 They contain granules that release
histamine, a substance involved in
allergic reactions.
 Basophils also produce substances that
attract neutrophils and eosinophils to a
trouble spot.

43. Natural killer cells
Natural killer cells
 are lymphocytes, a type of white blood cell.
Natural killer cells are called "natural" killers
because they are ready to kill as soon as
they are formed.
 attach to foreign cells and release enzymes
and other substances that damage the outer
membranes of the foreign cells.
 kill certain microorganisms, cancer cells, and
cells infected by viruses. Thus, natural killer
cells are often the body's first line of defense
against viral infections. Also, natural killer
cells produce cytokines that regulate some of
the functions of T lymphocytes, B
lymphocytes, and macrophages.

44.  The complement system consists of more than
30 proteins that act in a sequence: One protein
activates another and so on.
 This sequence is called the complement
cascade. Complement proteins can kill bacteria
directly or help destroy bacteria by attaching to
them, thus making the bacteria easier for
neutrophils and macrophages to identify and
ingest.
 Other functions include attracting macrophages
and neutrophils to a trouble spot, causing
bacteria to clump together, and neutralizing
viruses.
 The complement system also participates in
specific immunity.
Complement System

45. Cytokines
Cytokines
 Cytokines are the messengers of the immune system.
White blood cells and certain other cells of the immune
system produce cytokines when an antigen is detected.
 There are many different cytokines, which affect different
parts of the immune system. Some stimulate activity.
 They stimulate certain white blood cells to become more
effective killers and to attract other white blood cells to a
trouble spot.
 Other cytokines inhibit activity, helping end an immune
response. Some cytokines, called interferons, interfere
with the reproduction (replication) of viruses. Cytokines
also participate in specific immunity.

46.  Specific (adaptive) immunity is not present at birth;
it is acquired.
 As a person's immune system encounters antigens,
it learns the best way to attack each antigen and
begins to develop a memory for that antigen.
specific immunity is so named because it tailors its
attack to a specific antigen previously encountered.
 The hallmarks of specific immunity are its ability to
learn, adapt, and remember.
Specific immunity takes time to develop after initial
exposure to a new antigen.
 However, because a memory is formed, subsequent
responses to a previously encountered antigen are
more effective and more rapid than those generated
by nonspecific immunity.

47. Lymphocytes
Lymphocytes
 Lymphocytes are the most important type
of white blood cell involved in specific
immunity.
 Dendritic cells, antibodies, cytokines, and
the complement system (which enhances
the effectiveness of antibodies) are also
involved.
 Lymphocytes enable the body to
remember antigens and to distinguish self
from nonself (foreign). Lymphocytes
circulate in the bloodstream and lymphatic
system and move into tissues as needed.

48.  The immune system can remember every
antigen encountered because lymphocytes
live a long time—for years or even decades.
When lymphocytes encounter an antigen for
the second time, they respond quickly,
vigorously, and specifically to that particular
antigen.
 This specific immune response is the reason
that people do not contract chickenpox or
measles more than once and that vaccination
can prevent certain disorders.
 Lymphocytes include B lymphocytes, T
lymphocytes, and natural killer cells (which
are involved in nonspecific immunity).

49. B Lymphocytes
B Lymphocytes
 B lymphocytes (B cells) are formed in the
bone marrow.
 B lymphocytes have particular sites
(receptors) on their surface where specific
antigens can attach.
 When a B lymphocyte encounters an antigen,
the antigen attaches to the receptor,
stimulating the B lymphocyte to change into
a plasma cell.
Plasma cells produce antibodies.
 These antibodies are specific to the antigen
that stimulated their production.

50. T Lymphocytes
T Lymphocytes
 T lymphocytes (T cells) are produced in the
thymus gland. There, they learn how to distinguish
self from nonself. Only the T lymphocytes that
tolerate the self-identification molecules are
allowed to mature and leave the thymus. Without
this training process, T lymphocytes could attack
the body's cells and tissues.
 Mature T lymphocytes are formed and stored in
secondary lymphoid organs (such as the spleen),
bone marrow, and lymph nodes. They circulate in
the bloodstream and the lymphatic system, where
they search for particular foreign or abnormal cells,
such as particular bacteria or cells infected by
particular viruses. T lymphocytes can attack
particular foreign or abnormal cells.

51. There are different types of T lymphocytes:
There are different types of T lymphocytes:
 Killer (cytotoxic) T cells
attach to foreign or abnormal cells (because they
recognize the antigens on these cells). Killer T cells kill
foreign or abnormal cells by making holes in the cell
membrane and injecting enzymes into the cells.
 Helper T cells
help B lymphocytes recognize and produce antibodies
against foreign antigens. Helper T cells also help killer
T cells kill foreign or abnormal cells.
 Suppressor T cells
produce substances that help end the immune
response.
Sometimes T lymphocytes—for reasons that are not
completely understood—develop without or lose the
ability to distinguish self from nonself. The result is an
autoimmune disorder, in which the body attacks its
own tissues

52. Dendritic Cells
Dendritic Cells
 Dendritic cells develop from monocytes and
reside mainly in tissues. Newly developed
dendritic cells ingest and break antigens
into fragments so that other immune cells
can recognize them—an activity called
antigen processing. A dendritic cell matures
after it is stimulated by cytokines at a site of
infection or inflammation. Then, it moves
from tissues to the lymph nodes where it
shows (presents) the antigen fragments to T
lymphocytes, which generate a specific
immune response.

53. Antibodies
Antibodies
 When a B lymphocyte encounters an
antigen, it is stimulated to mature into a
plasma cell, which then produces
antibodies (also called immunoglobulins, or
Ig).
 Antibodies protect the body by helping
other immune cells ingest antigens, by
inactivating toxic substances produced by
bacteria, and by attacking bacteria and
viruses directly.
 Antibodies also activate the complement
system.
 Antibodies are essential for fighting off
certain types of bacterial infections.

54.  An antibody molecule is basically shaped
like a Y.
 The molecule has two parts.
 One part varies from antibody to antibody,
depending on which antigen the antibody
targets.
 The antigen attaches to the variable part.
The other part (constant part) is one of five
structures, which determines the antibody's
class—IgG, IgM, IgD, IgE, or IgA.
 This part is the same within each class.

55.  Figure 1 artikel 3
Carboxy terminal
Amino terminal
Light chain
Light chain
Interchain
disulfide bonds

56. Immunoglobulin
Immunoglobulin

57.  IgM:
This class of antibody is produced when a
particular antigen is encountered for the
first time.
The response triggered by the first
encounter with an antigen is called the
primary antibody response.
Normally, IgM is present in the
bloodstream but not in the tissues.

58.  IgG:
The most prevalent class of antibody, IgG is
produced when a particular antigen is
encountered again.
This response is called the secondary
antibody response.
It is faster and results in more antibodies than
the primary antibody response.
IgG is present in the bloodstream and
tissues. It is the only class of antibody that
crosses the placenta from mother to fetus.
The mother's IgG protects the fetus and infant
until the infant's immune system can produce
its own antibodies.

59.  IgE:
These antibodies trigger immediate allergic
IgE binds to basophils (a type of white
blood cell) in the bloodstream and mast
cells in tissues.
When basophils or mast cells with IgE bound
to them encounter allergens (antigens that
cause allergic reactions), they release
substances that cause inflammation and
damage surrounding tissues.
Thus, IgE is the only class of antibody that
often seems to do more harm than good.
However, IgE may help defend against
certain parasitic infections that are common
in some developing countries.

60.  IgA:
These antibodies help defend against the
invasion of microorganisms through body
surfaces lined with a mucous membrane,
including those of the nose, eyes, lungs,
and digestive tract.
IgA is present in the bloodstream, in
secretions produced by mucous
membranes, and in breast milk.
 IgD:
Small amounts of these antibodies are
present in the bloodstream.
The function of IgD is not well understood.

61. Strategies for Attack
Strategies for Attack
 Different types of invading microorganisms are
attacked and destroyed in different ways.
Some microorganisms are directly recognized, ingested,
and destroyed by phagocytes, such as neutrophils and
macrophages.
 However, phagocytes cannot recognize certain bacteria,
because the bacteria are enclosed in a capsule.
 In these cases, B lymphocytes have to help phagocytes
with recognition. B lymphocytes produce antibodies
against the antigens contained in the bacteria's
capsule. The antibodies attach to the capsules.
 The phagocyte can then recognize and ingest the whole
complex, including the bacteria.

62.  Some microorganisms cannot be completely
eliminated.
 To defend against these microorganisms, the
immune system builds a wall around them.
The wall is formed when phagocytes, particularly
macrophages, adhere to each other.
The walled microorganism is called a granuloma.
 Some bacteria thus imprisoned may survive in the
body indefinitely.
 If the immune system is weakened (even 50 or 60
years later), the walls of the granuloma may
crumble, and the bacteria may start to multiply,
producing symptoms.

63. Aging & Immune Function
Aging & Immune Function
 The immune system helps repair a person's DNA.
It also helps prevent infections caused by fungus,
bacteria, viruses and other organisms.
Immune system functioning changes with age.
 The immune system's job is to seek out and
destroy invaders that can harm the body.
The ability of the immune system to fight
infections declines with age. This does not mean
that people necessarily get sick more often. But,
as they get older, the risk of illness increases.

64. Aging & Immune Function
Aging & Immune Function
 As the immune system fails, elderly people
are subject to infections, cancer,
autoimmune disorders, or disorders
directed against the body's own tissue, and
to many chronic diseases.
 This may be due to the natural course of
these diseases. Many diseases develop
slowly and symptoms do not show up until
later in life.
 With age, many of the disease-fighting
cells, called T-cells, or T lymphocytes, lose
the ability to function.

65. The body retains the same number of T-cells as
before, but these cells are less able to control
illness than the cells were in earlier years.
Another function of the immune system is to
produce antibodies to ward off foreign invaders
in the body, such as bacteria and viruses.
These antibodies produced by the immune
system are a type of protein called
immunoglobulins. As people age, their immune
systems produce smaller quantities of
antibodies.
This means that vaccinations such as flu shots
may provide less protection than when a
person was younger.

66. • Another problem is that the body can lose its
ability to distinguish what is foreign and what is
part of itself.
• When this occurs, it can lead to autoimmune
disease. It also means that the immune system
cannot identify and fight cancerous, or malignant
cells.
• This is one of the reasons that the risk of many
cancers increases with age.

67. .
•Finally, people lose nerve endings and skin
cells with age.
• This increases the risk of injury. Cuts or
openings in the skin allow bacteria to enter
the body.
•Fighting off infection further taxes the
immune system, creating a vicious cycle.

68. To minimize the risk of infection
To minimize the risk of infection
and individuals should
and individuals should
 keep vaccinations up to date.
immunization to prevent pneumonia.
against hepatitis, have flu shot every year,
and get a tetanus shot every 10 years.
 exercise daily and eat a well balanced diet
 stop smoking.
 minimize alcohol use.
 get plenty of rest.
 maintain an active lifestyle
 implement home safety measures to
reduce the chance of injury.

69. Pustaka
Pustaka
Immune system
 Levinson, WE ang Jawetz, E. 2004
 Medical Microbiology & Immunology1.
Immune system and aging
 Burns EA, 2001.
Associate Professor of Medicine (Geriatrics)
Medical College of Wisconsin
Healthlink Medical College of Wincosin
 2002
 Artikel 3, february 2003
 HealthAnswers, 2008.