- The Immune
- Nonspecific Defense
- A). Skin and Mucus
- If not broken, the skin is an impenetrable
barrier to viruses and bacteria.
- It is reinforced by chemical defenses. Oil and
sweat give the skin a pH of 3-5.
- Bacteria that live on the skin help by
releasing acids and wastes to kill off unwanted microorganisms.
Lysozyme is found in tears and saliva which can destroy the cell
walls of most bacteria. Gastric juices kill off bacteria in food.
Mucus captures bacteria in the nose and throat cavities of the
- B). Phagocytes and Natural Killer
- Phagocyte are cells that eat
other cells or objects found in the body.
- Macrophages a type of phagocyte that eats
bacteria, viruses, and the debris of damaged cells. They develop
from a class of white blood cells called
MONOCYTES. Neutrophils are another
type of white blood cell capable of becoming
- Natural Killer Cells destroy the
bodies own infected cells, especially those containing viruses.
They may attack cells that might form tumors. They do not eat the
cell but lyse it
- C). Inflammatory Response
- Damage to tissue by physical injury will
trigger an inflammatory response.
- Small blood vessels in the area will dilate
and become leakier. This causes the redness and heat of the
infected area. This enhances the migration of phagocytes into the
area. Neutrophils arrive first,
followed by monocytes that develop
into macrophages. Clotting proteins
seal off the infected area.
- Injured cells release
HISTAMINE which induces the dilation
of the capillaries.
- Sometimes white blood cells release chemicals
called pyrogens. They act on the
bodies thermostat and raise the temperature in an effort to kill
- Anti microbial
- Interferons: Acts in warning other
cells of a viral invasion. It is produced by infected
- Complement: Circulate in the body in an
inactive form. They are activated by chemical markers, or the
onset of the immune response.
- SPECIFIC DEFENSE
- Immune Response = a recognition
system that distinguishes "self" form "non-self".
- Antigen = Foreign
- Antibody = specific defensive
proteins which help to counter antigens is various
- Immunity = protection afforded
to an organism by previous exposure to an antigen.
- Active Immunity = Immunity
conferred by an encounter with the actual virus or bacterium. The
body actually produces antibodies in its own defense.
- Passive Immunity = Temporary
acquired antibodies passed on to the organism. No antigen is
- The Immune
response is governed by 2 different parts of
the immune system.
- Humoral Immunity: results in the
production of antibodies that circulate around the body in blood
and lymph (humors). Defends against: free bacteria and
- Cell-mediated Immunity: defense
activities are carried out by specialized cells circulating around
the body. Defends against: host cells infected with bacteria and
viruses, fungi and protozoans, tissue transplants, own cancer
- Cells of the Immune
- Lymphocytes: White blood cells that are
divided into 2 types:
- B lymphocytes or B cells = secrete
antibodies act in humoral immunity.
- T lymphocytes or T cells = function in
- Both originate from the bone marrow. They
become B or T depending on their point of maturation. The
T develop in the
THYMUS gland found in the chest. The
B develop in the
bone. After this maturation process
is complete they attain
IMMUNOCOMPETENCE. This is their
ability to do their appointed jobs.
- These cells eventually migrate to the lymph
nodes and spleen waiting for their appropriate antigens to
The Humoral Immune Response: is provoked by
the binding of antigens to specific receptors sticking out of the
plasma membrane of B cells. This occurs most commonly in the lymph
Activation of B cells:
1. Capping: The
serial (many repeated forms of antigens) antigenic determinants bind
to several antibodies on the surface of the B cell. Pulling the
antibodies together. The B cell is activated when this whole cluster
is ingested by the cell.
2. Help from specialized T
cells: Helper T cells release a chemical called
interleukin II. This double action ( antigen and interleukin II)
results in a clone of plasma cells, which secrete antibodies against
the free antigens.
Each B cell is coated with only one type of
receptor. They are considered selective in nature. Once an activated
B cell begins to grow and multiply, this clone includes memory cells
and effectors cells called plasma cells. B cells secrete very few
antibodies but the plasma calls give off as many as 2000 antibodies
per sec. for their 4-5 day life span.
Antibody Structure: Antibodies constitute a
class of plasma proteins called Immunoglobulins, abbreviated Ig.
These antibodies have the ability to recognize and help destroy
specific antigens in the body. Each molecule consists of 2 distinct
regions. a). the variable region (V) and b). the constant
A typical antibody consists of 2 pairs of
polypeptide chains- 2 short identical light(L) chains and 2 longer
identical heavy(H) chains. The chains are joined by disulfide bridges
and non covalent associations to form a Y shaped molecule. The ends
of the Y contain the antigen binding sites.
- IgA: found in body secretions, help
attach antigen to body wall where they can be swept
- IgM: largest of the antigens, produced
early in infection, helps produce complement.
- IgG: most abundant of circulating
antibodies, confers passive immunity in babies, occurs when
infection is well established, also activates complement
- IgD: always bound to the plasma
membrane of B cells,
- IgE: associated with the bodies
allergic responses, binds to mast cells which release
Humoral Effector mechanisms: Antibodies do
not posses the power to destroy the antigens directly, they tag them
and mark them for destruction by a variety of effector
- Neutralization: surround the antigen
cutting it off from the organism, phagocytes then dispose of the
- Agglutination: bind together many
antigens into clumps for phagocytes to eat.
- Precipitation: binding together of
antigen molecules (not cells) for removal by
- Activation of the Complement system:
These chemicals will lyse the invader and make it easier for
phagocytes to do their work.
Cell Mediated Immunity: Once pathogens have
invaded the body's cells, antigens cannot harm them. This type of
immunity destroys the invaded cells directly. This type of immune
response cannot be activated by direct antigen contact. T cells only
react to the antigenic determinants displayed on the cell surface of
the body's own cells. These are called T-Cell receptors.
T-cell Receptors and Histocompatibility
The T-cell receptor actually recognizes a
combination of the antigen along with the body's "self" markers.
"Self" is signaled by the major histocompatibility complex (MHC), a
group of proteins unique to the individual that is present on the
surface of the cell. There are 2 forms of MHC: MHCI and MHCII. I is
found on nucleated cells
of the body, II is found on macrophages, B cells
and some T cells. The T-cell recognized both types of proteins at
once. This complex as as a red flag to the T cells.
They will divide and produce memory cells and
effectors called cytotoxic T cell.
There are 2 types of T cells with regulatory
functions within the body. helper-T cells and suppressor T
Helper T cells: They eat the antigen,
digest it and display parts of it on their cell surface. They bind
with macrophages causing the macrophages to release a chemical called
interleukin I, which stimulates the reproduction of the T cells. The
activated T cells then produce a chemical called interleukin II, this
increases the division and growth rate of the T cells. This is an
example of positive feed back.
Cytotoxic T Cells: These are the only T
cells that can kill off other cells. They recognize the cells by the
MHC-antigen complex. They release a chemical called
Suppressor T cells: They release cytokines
that inhibit the activity of other T cells.