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Dr. Chhaya Sawant
Our bodies are constantly at war and are underOur bodies are constantly at war and are under
attack,attack, 24-hours a day from infection and toxins.24-hours a day from infection and toxins.
Crossing the barriersCrossing the barriers
If physical & chemical barrier is brokenIf physical & chemical barrier is broken
down by:down by:
- as result of infection on surface
invading microorganisms can enter body,invading microorganisms can enter body,
blood stream & lymphatic system.blood stream & lymphatic system.
Inside the body, pathogens can find aInside the body, pathogens can find a
niche in body tissue to multiply andniche in body tissue to multiply and
causes diseases.causes diseases.
That we survive at all, is due toThat we survive at all, is due to
our immune system.our immune system.
- a network of chemicals & cells- a network of chemicals & cells
that protect the body.that protect the body.
In humans, the immune system begins to develop in the embryo. The immune
system starts with hematopoietic (from Greek, "blood-making") stem cells.
What is Immunity?
The immune system is
localized in several parts
of the body
Immune cells develop in
the primary organs -
bone marrow and thymus
Immune responses occur
in the secondary organs
ANATOMY OF THE IMMUNE SYSTEM
• Thymus – glandular organ near the heart – where T cells learn
• Bone marrow – blood-producing tissue located inside certain
– blood stem cells give rise to all of the different types of blood cells
• Spleen – serves as a filter for the blood
– removes old and damaged red blood cells
– removes infectious agents and uses them to activate cells called
• Lymph nodes – small organs that filter out dead cells, antigens,
and other “stuff” to present to lymphocytes
• Lymphatic vessels – collect fluid (lymph) that has “leaked” out
from the blood into the tissues and returns it to circulation
Humans have three types of immunity
– Innate, non-specific
– Helper T
– Cytotoxic T
YOUR ACTIVE IMMUNE DEFENSES
- invariant (generalized)
- early, limited specificity
- the first line of defense
- variable (custom)
- later, highly specific
- ‘‘remembers’’ infection
1. Barriers - skin, tears
2. Phagocytes - neutrophils,
3. NK cells and mast cells
4. Complement and other proteins
Antibodies (Y) are also found
in breast milk.
The antibodies received
through passive immunity
last only several weeks.
While your immune system was developing, you were
protected by immune defenses called antibodies. These
antibodies traveled across the placenta from the maternal
blood to the fetal blood.
Major Principles of Immunity
• Elimination of many microbial agents through the
nonspecific protective mechanisms of the innate
• Highly specific recognition of foreign antigens coupled
with potent mechanisms for elimination of microbes
bearing such antigens
• A vast universe of distinct antigenic specificities and a
comparably vast capacity for the recognition of these
• The capacity of the system to display immunologic
• Tolerance of self-antigens
Function of Immune System is
3. Fungus/ multicellular parasites
6. ( 5,000 daltons--
Normally our bodies are fit enough toNormally our bodies are fit enough to
fight an infection with all the parts offight an infection with all the parts of
our immune system.our immune system.
Sometimes we need help fighting
B cells and T cells are the main types of lymphocytes.
B-Cells: stored and mature in spleen
Bone Marrow PeripheryBone Marrow Periphery
Primary Lymphoid Organ Secondary Lymphoid Organs
• secrete highly specific Ab to bind foreign substance (antigen: Ag),
form Ab-Ag complex
• responsible for humoral response
• perform antigen processing and presentation
• differentiate into plasma cells (large Ab secretion)
Overview of B-Cell Development
T cells: stored & mature in thymus-migrate throughout the body
Enhance T killer or B cell activity
Perform lysis (infected cells)
Cell mediated immune response
Reduce/suppress immune activity
May help prevent auto immune disease
ORGAN AND T-CELL DEVELOPMENT
LIVER - (4 Weeks)
BONE MARROW - (4-5 Weeks )
THYMUS - (7-10 Weeks)
BLOOD LYMPH - (14 Weeks)
SPLEEN - (16 Weeks)
• Phagocytes include
- Monocytes, which circulate in the blood;
- Macrophages, which are found in tissues throughout the body;
- Dendritic cells, which are more stationary, monitoring their environment
from one spot such as the skin
- Neutrophils, cells that circulate in the blood but move into tissues when
they are needed.
2. Neutrophils (Phagocytes)- found throughout body, in
blood - phagocytosis of Ab-Ag CX
3. Macrophages- throughout body, blood, lymphatics
-phagocytose non-specifically (non Ab coated Ag)
-phagocytose specifically Ab-Ag CX
-have large number of lysosomes (degradative enzyme)
-perform Ag processing and presentation
-present Ag to T helper cell
-secrete lymphokines/ cytokines to stimulate T helper
cells and immune activity
4. Natural Killer Cells- in blood throughout body
-destroy cancer cells
-stimulated by interferons
IgG, the major immunoglobulin in the blood, is also able to enter
tissue spaces; cross placental barrier, fix complement, induce
macrophage engulfment efficiently to coat microorganisms,
speeding their destruction by other cells in the immune system.
IgD is almost exclusively found inserted into the membrane of B
cells, where it somehow regulates the cell's activation.
IgE is normally present in only trace amounts, but it is
responsible for the symptoms of allergy.
IgA--a doublet--guards the entrance to the body. It concentrates
in body fluids such as tears, saliva, and secretions of the
respiratory and gastrointestinal tracts.
IgM usually combines in star-shaped clusters. It tends to remain
in the bloodstream, where it is very effective in killing bacteria, fix
complement, induce macrophage engulfment, primary immune
Antibodies belong to a family of large protein molecules known as immunoglobulins.
Different classes play different roles in the immune defense strategy.
Scientists have identified nine chemically distinct classes of human immunoglobulins:
four kinds of IgG and two kinds of IgA, plus IgM, IgE, and IgD.
Immunoglobulins G, D, and E are similar in appearance.
The complement system
A series of about 25 proteins that work to "complement" the
work of antibodies in destroying bacteria.
Series of enzymes which are sequentially
activated and result in lysis of cell
membrane of infected cell of bacterium
Permeablizes membrane leaky
Complement binding and
~35 enzymes and factors
involved in cascade
Activation of B Cells
Things That Can Go Wrong With the
Disorders of the immune system can be broken down
into four main categories:
• Immunodeficiency disorders (primary or acquired)
• Autoimmune disorders (in which the body's own immune system attacks
its own tissue as Foreign matter)
• Allergic disorders (in which the immune system overreacts in response to
• Cancers of the immune system
The immune response to an antigen is
potentially a "two-edged sword“
May either protect or harm the host.