History
Emil von Behring 1880’s- Metchnikoff
Shibasaburō discovered phagocytic
cells that ingest microbes
Kitasato and particles
- cells conferred immunity
1890- von Behring and
Kitasato discovered blood
sera could transfer
immunity
- liquid of blood conferred
immunity
By Dr. Anna Sukiasyan
Elie Metchnikoff
Both cells and serum contribute to immunity!
• 1930’s – early techniques made it easier to
study humoral elements [than cellular
ones].
-discovery of active component of blood –
gamma globulin “protein”
• 1950’s – discovery of T and B cells
Later discoveries linked lymphocytes to
both cellular and humoral immunity
Understanding specificity of antibody for antigen took years
Karl Landsteiner
• Early 1900’s-
Landsteiner revealed
antibody could be
produced vs. most any
organic compound
• Last 20 yrs- Antibody
specificity reveals
unlimited range of
reactivity – also to
newly synthesized
chemicals!
Paul Erlich’s side chain hypothesis for antibody
formation (1900)
• Contact with foreign
molecules (antigen)
stimulated increased
receptor production
• Specific receptors
produced on cells prior to
contact with antigen
Sir Alexander Fleming (1881-1955)
They discovered the first relatively safe and effective
antibiotics (of natural origin) – isolated from
microorganisms.
Fleming discovered penicillin, Waksman discovered
streptomycin and a number of other antibiotics.
Louis Pasteur (1822-1895).
In 1885, Pasteur administered his first vaccine to a human against the
rabies disease
Later, Pasteur - introduced pasteurization also
Recognized and exploited the general principle underlying vaccination
Introduction
Immunology has its origins in the study of how the body protects
itself against infectious diseases caused by microorganisms, such as
bacteria, viruses, protozoa, and fungi, and also parasitic organisms,
such as helminth worms.
Important initial barriers to infection are physical (e.g. the skin),
enhanced by substances secreted by the body, such as saliva and
tears, that contain molecules that can neutralise bacteria.
The internal mucosal tissues (e.g. lungs and airways, and the gut)
are coated with mucus that is able to trap potential infectants.
In the airways, mobile ciliate hairs work together to transport
contaminants away from vulnerable areas.
Tissues such as the skin, mucosal surfaces and airways also contain
populations of immune cells that can respond to infectants that
breach these physical defences.
Types Of Immunity
• Inborn or innate immunity: It is present at birth; This
is our First Line Of Defense.
• Acquired or specific: It is not present at birth but
becomes part of our immune system as the lymphoid
system develops.
• 1970: WHO defined immunity as immune response
to antigen ( Foreign body) in form of
• Humoral ( activation of B-lymhocytes)
• Cellular (by activation of T-lymphocytes)
Immune tissues
All immune cells originate in the bone marrow,
deriving from haematopoietic stem cells, but an
important set of immune cells (T lymphocytes)
undergo maturation in an organ known as the
thymus.
The thymus and bone marrow are known as
primary lymphoid tissues.
Secondary lymphoid tissues, namely the lymph nodes, spleen
and mucosa-associated lymphoid tissues (MALT) are important
sites for generating adaptive immune responses and contain the
lymphocytes (key adaptive cells).
The lymphatic system is a system of vessels draining fluid
(derived from blood plasma) from body tissues.
Lymph nodes, that house lymphocytes, are positioned along
draining lymph vessels, and monitor the lymph for signs of
infection.
MALT tissues are important in mucosal immune responses, and
reflect the particular importance of the gut and airways in
immune defence.
The spleen essentially serves as a ‘lymph node’ for the blood.
In its most complex forms, the immune system consists
of two branches:
the innate immune system that utilises certain ‘hard-
wired’ strategies to provide a rapid, general, response
when alerted by certain typical signals of infection
(essentially forming a first-line of defence);
and the adaptive immune system that is able to
develop highly specific responses (and a persistent
‘immune memory’) to target infection with
extraordinary accuracy.
Both systems work in close cooperation and, to an
important extent, the adaptive immune system relies
upon the innate immune system to alert it to potential
targets, and shape its response to them.
Immune System
Organs
The key primary
lymphoid organs of the
immune system
include the thymus
and bone marrow,
as well as secondary
lymphatic tissues
including spleen,
tonsils, lymph vessels,
lymph nodes,
adenoids, skin, and
liver.
Immune System Organs. Primary immune organs.
The thymus “educates” T cells and provides an inductive
environment for the development of T cells from
hematopoietic progenitor cells. The thymus is largest and most
active during the neonatal and pre-adolescent periods of
development. Nevertheless, residual T-lymphopoiesis
continues throughout adult life.
Bone marrow is the flexible tissue found in the interior of
bones. The red bone marrow is a key element of the lymphatic
system, being one of the primary lymphoid organs that
generate lymphocytes from immature hematopoietic
progenitor cells. Bone marrow and thymus constitute the
primary lymphoid tissues involved in the production and early
selection of lymphocytes.
Immune System Organs. Secondary immune organs.
The lymphatic system is a part of the circulatory system,
comprising a network of conduits called lymphatic vessels that
carry a clear fluid, called lymph, unidirectionally towards the
heart. The lymphatic system has multiple interrelated functions
including the transportation of white blood cells to and from the
lymph nodes into the bones, and the transportation of antigen -
presenting cells (such as dendritic cells) to the lymph nodes
where an immune response is stimulated. Lymphoid tissue is
found in many organs, particularly the lymph nodes.
The spleen is similar in structure to a large lymph node and acts
primarily as a blood filter. It synthesizes antibodies in its white
pulp and removes antibody-coated bacteria along with antibody-
coated blood cells by way of blood and lymph node circulation.
Immune System Organs. Secondary immune organs.
The palatine tonsils and the nasopharyngeal tonsil are
lymphoepithelial tissues located near the oropharynx and nasopharynx.
These immunocompetent tissues are the immune system’s first line of
defense against ingested or inhaled foreign pathogens.
Lymph nodes are distributed widely throughout areas of the body,
including the armpit and stomach, and linked by lymphatic vessels.
Lymph nodes are garrisons of B, T and other immune cells. Lymph
nodes act as filters or traps for foreign particles and are important in
the proper functioning of the immune system. They are packed tightly
with the white blood cells, called lymphocytes and macrophages.
Immune System Organs. Secondary immune organs.
The skin is one of the most important parts of the body because it
interfaces with the environment, and is the first line of defense from
external factors, acting as an anatomical barrier from pathogens and
damage between the internal and external environment in bodily
defense. Langerhans cells in the skin are part of the adaptive immune
system.
The liver has a wide range of functions, including immunological
effects—the reticuloendothelial system of the liver contains many
immunologically active cells, acting as a “sieve” for antigens carried to
it via the portal system.
Cells of the Immune System
All the cells of the immune system arise from a single hematopoietic stem cell (HSC).
Actually, HSC can give rise to three different types of progenitor cells, namely, lymphoid
progenitor, myeloid progenitor and erythroid progenitor. Basically, lymphoid and
myeloid progenitors give rise to immune cells and erythroid progenitor gives rise to
other types of blood cells.
THE IMMUNE RESPONSE AND IMMUNITY
Immune System
Innate Adaptive
(Nonspecific) (Specific)
1o line of defense 2o line of defense
Interactions between the two systems
Humoral
Cellular
DEFENSE MECHANISMS OF THE HUMAN HOST
• Innate Mechanisms (Innate immunity)
– First line of defense
– Non-specific
• Adaptive Mechanisms (Adaptive immunity)
– Second line of defense
– Highly specific with memory
• Cooperation between mechanisms
Innate immunity vs Adaptive Immunity
Innate Immunity Adaptive Immunity
(first line of defense) (second line of defense)
No time lag (Lymphocyte-activation gene) A lag period
Not antigen specific Antigen specific
No memory Development of memory
The human body is a compound wall is the first line of defense or equivalent of innate
immunity. It does not allow entry into the body. Not speific for any pathogen. It has no
memory (It does not remember the pathogen).
If pathogen manages to get into the body. Then the second line of defense - get into
action. They identify the pathogen and pin him down and get him out. Activate and
mobilize resources, they just target a specific pathogen and they remember the pathogen
(it`s a Memory).
A typical immune response
ACQUIRED IMMUNITY
INNATE IMMUNITY Slower responses to
Rapid responses to a specific microbes
broad range of microbes
External defenses Internal defenses
Skin Phagocytic cells
Humoral response
Mucous membranes Antimicrobial proteins (antibodies)
Secretions Inflammatory response
Invading
microbes Natural killer cells Cell-mediated response
(pathogens) Complement (cytotoxic
lymphocytes)
