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Lectures in periodontics – 4th stage
Host immunity part -1Assist. Lec. Fahad M. al Dabbagh
Immunity: refers to a state of acquired or innate resistance or protection
from a pathogenic microorganism or its products or from the effect of toxic
substances such as snake or insect venom.
Immunology: is that branch of biomedical science concerned with the
response of the organism to immunogenic(Antigenic) challenge, the
recognition of self from nonself, and all the biological (in vivo), serological (in
vitro, physical, and chemical aspects of immune phenomena.
Immune system: is a network of cells, tissues, and organs that work together
to defend the body against attacks by “foreign” invaders. These are primarily
microbes (germs) tiny, infection-causing organisms such as bacteria, viruses,
parasites, and fungi.
Antigen: is a substance or molecule that is recognized by the immune system.
An antigen can be a microbe such as a virus, or even a part of a microbe.
Tissues or cells from another person (except an identical twin) also carry non
self-markers and act as antigens. This explains why tissue transplants may be
rejected.
Antibody: is molecule (also called immunoglobulin) produced by a B cell in
response to an antigen. When an antibody attaches to an antigen, it helps the
body destroy or inactivate the antigen. An antibody is made up of two heavy
chains and two light chains. The variable region, which differs from one
antibody to the next, allows an antibody to recognize its matching antigen.
Lectures in periodontics – 4th stage
Host immunity part -1Assist. Lec. Fahad M. al Dabbagh
Although antibodies can bind to and neutralize bacterial toxins directly, they
exert most of their effect by binding to the surface of bacteria, viruses, or other
parasites, and thus increasing their adherence to, and phagocytosis by, myeloid
cells. This phenomenon is known as opsonization. Antibody also activates
complement on the surface of invading pathogens
Lymphoid organs: the organs of the immune system, where lymphocytes
develop and congregate. They include the bone marrow, thymus, lymph nodes,
spleen, and various other clusters of lymphoid tissue. Blood vessels and
lymphatic vessels are also lymphoid organs.
Lymph: a transparent, slightly yellow fluid that carries lymphocytes,
bathes the body tissues, and drains into the lymphatic vessels.
Lymph nodes: small bean-shaped organs of the immune system distributed
widely throughout the body and linked by lymphatic vessels. Lymph nodes are
garrisons of B, T, and other immune cells.
Lymphocytes: small white blood cells produced in the lymphoid organs and
paramount in the immune defenses. B cells and T cells are lymphocytes.
- Immune responses are categorized as:
1-
Innate immune responses: rapid and immediate host response to
entry of a foreign pathogen and usually includes the physical, chemical
and microbiological barriers.it do not adapt with repeated exposure to
the same pathogen. An example of innate immunity is phagocytic cells
(i.e., monocytes, macrophages, and neutrophils), which possess a
number of inherently antimicrobial peptides and proteins that kill many
different, rather than one specific pathogen.
2- Specific adaptive immune responses will increase after exposure to
a pathogen. Lymphocytes (e.g., T-cells and B-cells) are important in the
fundamental form of specific adaptive immunity. The ability of T-cells
and B-cells to recognize specific oligomeric structures on a pathogen and
generate progeny that also recognize the structure enables the immune
system to respond more rapidly and effectively when exposed to that
pathogen again.
Lectures in periodontics – 4th stage
Host immunity part -1Assist. Lec. Fahad M. al Dabbagh
The main cells of the immune system are derived from the lymphoid and
myeloid arms of the hematopoietic system.
a- In the bone marrow, the myeloid arm gives rise to:
1- Peripheral dendritic cells,
2- phagocytes (neutrophils and monocytes),
3- mast cell precursors,
4- basophils,
5- eosinophils,
6- platelets,
7- Erythrocytes.
b- In the bone marrow, the lymphoid arm gives rise to:
1- NK-cells,
2- B-cells,
3- Pre-T-cells (differentiate to T-cells in the thymus).
In the tissues:
1- Peripheral dendritic cells,
2- Monocytes (can become a macrophage)
3- Mast cell precursors further differentiate.
In secondary lymphoid organs, including lymph nodes and the spleen:
1- They are areas where antigen presenting cells, (B-cells and dendritic
cells) present antigen to T-cells.
2- Terminal differentiation of B- and T-cells also occurs in these organs.
Lectures in periodontics – 4th stage
Host immunity part -1Assist. Lec. Fahad M. al Dabbagh
Cells of immunity responses:
- Cells possess receptors, (which are molecules on the cell surfaces that
enable the cell to interact with other molecules or cells.
- Receptors reflect and dictate the function of cells. Historically, the names
given to receptors often related to function.
- Cells of the immune system those are important in inflammation and
host defenses include in mast cells, dermal dendrocytes (histiocytes),
peripheral dendritic cells, neutrophils, monocytes/macrophages, T-cells,
B-cells, and NK-cells.
Lectures in periodontics – 4th stage
Host immunity part -1Assist. Lec. Fahad M. al Dabbagh
Other hematopoietic leukocytes (i.e., basophils, eosinophils,
erythrocytes, and platelets) also participate in certain forms of
inflammation or immune function.
1- B cell: is a small white blood cell crucial to the immune defenses. Also
known as B lymphocytes, they come from bone marrow and develop into
blood cells called plasma cells, which are the source of antibodies.
- Plasma cells: large antibody-producing cells that develop from B cells.
2- T cells: small white blood cells (also known as T lymphocytes) that
recognize antigen fragments bound to cell surfaces by specialized antibodylike receptors. “T” stands for thymus, where T cells acquire their receptors.
There are two types of T cells:
a-
Helper T cell (TH cell): is a subset of T cell that carries the CD4 surface
marker and are essential for turning on antibody production, activating
cytotoxic T cells, and initiating many other immune functions.
b-
Cytotoxic T lymphocytes, which are the main immunological effector
mechanisms involved in the elimination of non-self or infected cells.
- Memory cells: a subset of T cells and B cells that have been exposed to
antigens and can then respond more readily when the immune system
encounters those same antigens again.
3. Antigen-presenting cells, such as the macrophages and macrophagerelated cells play a very significant role in the induction stages of the immune
response by trapping and presenting both native antigens and antigen
fragments in a most favorable way for the recognition by lymphocytes. In
addition, these cells also deliver activating signals to lymphocytes engaged in
antigen recognition, both in the form of soluble mediators (interleukins such as
IL-12 and IL-1) and in the form of signals delivered by cell-cell contact.
4. Phagocytic and cytotoxic cells, such as monocytes, macrophages, and
granulocytes, also play significant roles as effectors of the immune response.
Once antibody has been secreted by plasma cells and is bound by the microbes,
Lectures in periodontics – 4th stage
Host immunity part -1Assist. Lec. Fahad M. al Dabbagh
cells, or compounds that triggered the immune response, it is able to induce
their ingestion by phagocytic cells. If bound to live cells, antibody may induce
the attachment of cytotoxic cells that cause the death of the antibody-coated
cell (antibody-dependent cellular cytotoxicity; ADCC). The ingestion of
microorganisms or particles coated with antibody is enhanced when an
amplification effector system known as complement is activated.
5. Natural killer (NK) cells: large granule-containing lymphocytes play a dual
role in the elimination of infected and malignant cells. These cells are unique in
that they have two different mechanisms of recognition: they can identify
directly virus-infected and malignant cells and cause their destruction, and they
can participate in the elimination of antibody-coated cells by ADCC.
- Phagocytes: large white blood cells that contribute to the immune
defenses by ingesting microbes or other cells and foreign particles.
- Phagocytosis: process by which one cell engulfs another cell or large
particle.
- Monocytes: large phagocytic white blood cells which, when entering
tissue, develop into macrophages.
- Macrophage: a large and versatile immune cell that devours invading
pathogens and other intruders. Macrophages stimulate other immune
cells by presenting them with small pieces of the invaders.
Lectures in periodontics – 4th stage
Host immunity part -1Assist. Lec. Fahad M. al Dabbagh
- Mast cell: a granulocyte found in tissue. The contents of mast cells,
along with those of basophils, are responsible for the symptoms of
allergy.
- Dendritic cells: A rare cell type found in the T cell area of all lymphoid
tissues, whose function is to present antigen to T cells, and thus initiate
all T cell-dependent immune responses. Not to be confused with
follicular dendritic cells, which store antigen for B cells
- Basophil: is a white blood cell that contributes to inflammatory
reactions. Along with mast cells, basophils are responsible for the
symptoms of allergy.
- Eosinophil: is a white blood cell that contains granules filled with
chemicals damaging to parasites, and enzymes that affect inflammatory
reactions.
- Complement: is a complex series of blood proteins whose action
“complements” the work of antibodies. Complement destroys bacteria,
produces inflammation, and regulates immune reactions.
- Immunoglobulin: is a family of large protein molecules, also known as
antibodies, produced by B cells.
- Cytokines: is a powerful chemical substances secreted by cells that
enable the body’s cells to communicate with one another. Cytokines
include lymphokines produced by lymphocytes and monokines produced
by monocytes and macrophages.