Immunology Ch1
 Immunity is defined as resistance to disease, specifically infectious disease.
 The physiologic function of the immune system is to prevent infection and to eradicate
established infections
 Vaccinations are the most effective method for protecting individuals against infections.
 Host defense mechanism consists of innate immunity which mediates the initial protection
against infections and adaptive immunity which develops more slowly and mediates the
later even more effective defense against infections.
 Innate immunity refers to the fact that this type of immunity is always present in
healthy individuals and block the entry of microbes into the body.
 The first line of defense in innate immunity is the epithelial cells which help to block
microbes from entering the body.
 Innate immunity consists of phagocytes called natural killer cells.
 The consume infectious agents called antigens
 Phagocytes including macrophages and neutrophils ingest microbes in vesicles
and destroy them by producing microbial substances in these vesicles,
macrophages and dendritic cells also produce soluble proteins called cytokins
which stimulate inflammation and lymphocyte response (adaptive immunity).
 Adaptive immunity is the type of host defense that is stimulated by microbes that
invade tissues and it adapts to the presences of microbial invaders.
 The adaptive system consists of lymphocytes and their products such as antibodies.
 Lymphocytes are specific which ensures that distinct antigens elicit specific
responses
 Lymphocytes are diverse which enables the immune system to respond to a large
variety of antigens
 Lymphocytes have a memory which leads to enhanced responses to repeated
exposure to the same antigens.
 When lymphocytes are activated by antigens they undergo proliferation which
generates many thousands of clonal progeny. This is called clonal expansion.
 Lymphocytes are the only cells that produce specific receptors for antigens and are
thus the key mediators of adaptive immunity.
 When naïve lymphocytes recognize microbial antigens and also receive additional
signals induced by microbes, the antigen specific lymphocytes proliferate and
differentiate into defector cells and memory cells.
 Effector cells differentiate and their function is to eliminate antigens
 Memory cells survive for long periods of time in the absence of an antigen.
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 The two types of adaptive immunity, humoral immunity and cell mediated immunity
which are mediated by different cells and molecules and are designed to provide
defense against extracellular microbes and intracellular microbes respectively.
 Humoral immunity consists of B cells which secrete antibodies
 Cell mediated Immunity consist of T cells
 The antigen receptors of most T lymphocyte only recognize peptide fragments of
protein antigens that are bound to specialized peptide display molecules called
major histocompatibility complex (MHC) molecules on the surface of specialized
cells called antigen presenting cells (APCs)
 T lymphocytes mature in an organ called the thymus.
 CD 4 T cells are called helper cells because they help B lymphocytes produce
antibodies
 CD 8 T cells are called cytotoxic or cytolytic because the kill (lyse) cells harboring
intracellular microbes.
Immunity may be induced in an individual by infection or vaccination (active immunity) or
conferred on an individual by transfer of antibodies or lymphocytes from an actively
immunized individual (passive immunity).
The common portals of entry for microbes the skin the gastrointestinal tract, respiratory
tract contain specialized antigen presenting cells (APC) located in the epithelium that
capture antigens transport them to peripheral lymphoid tissue and display them to
lymphocytes.
The tissue of the immune system consist of generative (also called primary or central)
lymphoid organs in which T and B lymphocytes mature and become competent to respond
to antigens and peripheral(or secondary) lymphoid organs in which adaptive immune
responses to microbes are initiated.
The peripheral lymphoid organs which consist of lymph nodes the spleen and the mucosal
and cutaneous immune system are organized to optimize interactions between antigens
APCs and lymphocytes in a way which promotes the development of apative immune
response.
 Naïve lymphocytes constantly recirculate between the blood and peripheral lymph
organs where they may be activated by antigens to befome effector cells and effector
lymphocytes migrate to the site of infection where microbes can be eliminated.
 T cells migrate more than B cells because B cells produce antibodies within the
lymph organ and the antibodies are secreted into the blood.
 Within the peripheral lymph organs (spleen) the T lymphocytes and B lymphocytes are
segregated to different anatomical positions
 B cells within the follicles of the spleen
 T cells within the paracortex of the spleen which contains dendritic cells.
Practice Questions
1. A young boy who lived all of his life in a glass room in a hospital in Pittsburgh Pa was
told that his body doesn’t produce any cells that give rise to adaptive immunity, but that
he did have cells derived through innate immunity. A blood sample would contain
which of the following cells:
A. T lymphocytes
B. Antibodies
C. Natural Killer cells
D. CD-4 cells
E. All of the above
The answer is c all of the other cells are contributors to adaptive immunity except Natural Killer
Cells
2. A two year old comes into contact with H1N1 for the first time in his life. The virus has
just gotten through his epithelial cells. Which lymphocyte is most likely to be seen in a
blood sample:
a. Effector T cells
b. Ig G
c. Memory B cells
d. Naïve Lymphocytes
The answer is d every other type of cell is specific and would have had to seen a particular
antigen before it could become one of these cells
3. CD4 cells (T helper cells ) are known to help which kind of cells
a. B cells
b. Cytolytic T cells
c. Cytotoxic cells
d. Antigen Presenting Cells
e. A, B, and C
The answer is E a T helper cells help B cells make antibodies. B and C are the same thing they
are both T killer cells which are helped by T helper cells. D is a kind of dendritic cell that shows
T cells if another cell is infected (not helped by T helper cells).
4. A 35 year old man was told that he has an infection that has never been seen before.
The infection is found inside 35% of his living cells. Which type of cell would you expect
to find in his blood sample
a. B lymphocytes
b. T lymphocytes
c. Antibodies made specific for this particular infection
d. Natural killer Cells
The answer is B T lymphocytes are presented intracellular peptides to see whether or not that
cells is infected. B cells, Natural Killer Cells, and antibodies would help to fight an infection that
was extracellular.
5. A medical student is looking at an antigen in blood through a very powerful microscope.
He sees the antigen covered in Y shaped cells. What is he looking at?
a. An APC cell attached to T cells
b. T killer cells fighting the antigen
c. B cells proliferating in response to the antigen
d. Antibodies coating the antigen
The answer is D the y shaped cells are characteristic of antibodies.