CELLS THAT DRIVE IMMUNE DEFENSE

CELLS INVOLVED
IN IMMUNE
RESPONSE
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• .
What is immune response?
• The immune response involves a coordinated set
of interactions among host cells and the
protective molecules they produce upon
encountering a pathogen or antigen.
• The purpose of which is to prevent dangerous
incursions and then to restore homeostasis

Cell Involved in
immune response
T-CELLS
B-CELLS
DENDRITIC
CELLS
MONO
CYTES
MACRO
PHAGES

T cells (also called T lymphocytes) are one of the main
components of the adaptive immune system. They are
vital in hosting an immune response against pathogen.
A type of white blood cell that is of key importance to the
immune system and is at the core of adaptive immunity,
the system that tailors the body's immune response to
specific pathogens. The T cells are like soldiers who search
out and destroy the targeted invaders.
T-CELLS

Production of T Cells
• T cells originate from stem cells which are produced in the bone
marrow.
• T cells then migrate to the thymus gland, in the anterior
mediastinum, to undergo the process of maturation. They enter the
cortex and proliferate, mature and pass onto the medulla of the
thymus.
• From the medulla, mature T cells enter the circulation. These mature
T cells are now capable of responding to antigens in the periphery.
• The thymus shrinks as we age and so provides fewer T cells over
time.

Types of T Cells
There are 4 main types of T cells.
They become activated when they are presented with peptide
antigens by MHC Class II molecules, which are expressed on the
surface of antigen presenting cells (APCs).
Helper T cells help in the maturation of B cells into plasma
cells and memory B cells. They also help activate cytotoxic T cells
and macrophages.
Once activated, they divide rapidly and secrete small proteins
called cytokines that regulate or assist in the active immune
response. There are various subtypes present within the immune
system that are able to secrete different cytokines depending on
the immune response occurring.
Helper T Cells1.

• Cytotoxic T cells cause lysis of virus-infected and tumour cells.
They are also involved in transplant rejection. These cells
recognize their targets by binding to antigen associated
with MHC Class I molecules which are present on the surface
of all nucleated cells.
2.Cytotoxic T Cells
3.Natural Killer T Cells
• Once they come into contact with an antigen naive T cells
differentiate into effector cells (Helper T cell and Cytotoxic T
cells) and memory T cells. Memory T cells are long-lived and
can quickly expand to large numbers of effector T cells
upon re-exposure to the antigen.
• They provide the immune system with “memory” against
previously encountered pathogens. Memory T cells may be
either Helper T cell and Cytotoxic T cells.
4.Memory T cells
They bridge the adaptive immune system with the innate immune
system. Whilst most T cells function based on recognition of MHC
class molecules, natural killer T cells are able to recognise other
antigen classes. Once activated they are also able to perform the
same functions as Helper T cells and Cytotoxic T cells.
These cells are distinct from natural killer cells.

What T cells do?
• T lymphocytes eliminate nascent tumors and
intracellular microorganisms such as viruses and some
bacteria, and regulate the strength of adaptive immune
responses. Functionally, T lymphocytes lyse malignant or
infected cells, induce inflammatory responses, and
synthesize and secrete soluble intercellular messengers
called cytokines.

How T-Cells Works
•Antigen-presenting cells must bind the processed antigens, first by using the major
histocompatibility complex (MHC) and then presenting it to the T lymphocytes.
1.With the help of other assistive molecules, the T lymphocytes are activated to
secrete effector proteins for clearing antigens. There are many ways to classify the T
lymphocytes; most accepted subpopulations are T help (TH), T cytotoxic (TC), and T
regulatory cells (Treg). TH cells have CD4 glycoprotein on their surfaces, TC cells
have CD8 glycoprotein, and Treg cells have CD4 on their membranes.
After encountering the right antigen-MHC complex, TH cells do not clear the antigens
directly but activate the B cells and TC cells to kill the pathogens. However, TC cells are
responsible for secreting proteins to destroy the pathogen cell wall and kill the
pathogens.

A type of white blood cell and, specifically, a type of lymphocyte.
Many B cells mature into what are called plasma cells that produce
antibodies (proteins) necessary to fight off infections while other B cells
mature into memory B cells.
The maturation of B cells takes place in birds in an organ called the bursa of
Fabricus. B cells in mammals mature largely in the bone marrow.
B cell activation occurs in the secondary lymphoid organs, such as
the spleen and lymph nodes.
B-CELLS

With the help of T-cells, B-cells make special Y-shaped
proteins called antibodies. Antibodies stick to antigens on
the surface of germs, stopping them in their tracks,
creating clumps that alert your body to the presence of
intruders. Your body then starts to make toxic substances
to fight them. Patrolling defender cells called phagocytes
engulf and destroy antibody-covered intruders.
What B-Cells do?

Activation of B-CELLS
• Activation of B cells occurs through different mechanisms depending on
the molecular class of the antigen. Activation of a B cell by a protein
antigen requires the B cell to function as an APC, presenting the protein
epitopes with MHC II to helper T cells. Because of their dependence on T
cells for activation of B cells, protein antigens are classified as T-
dependent antigens.
• In contrast, polysaccharides, lipopolysaccharides, and other nonprotein
antigens are considered T-independent antigens because they can
activate B cells without antigen processing and presentation to T cells.

T Cell-Independent Activation
of B cells
• Activation of B cells without the cooperation of
helper T cells is referred to as T cell-
independent activation and occurs when BCRs
interact with T-independent antigens(e.g.,
polysaccharide capsules, lipopolysaccharide).
• Once a B cell is activated, it undergoes clonal
proliferation and daughter cells differentiate
into plasma cells. Plasma cells are antibody
factories that secrete large quantities of

T cell-dependent
activation
Antigens that activate B cells with the help of T-cell are known as T cell-dependent
antigens and include foreign proteins.
Once a BCR binds a TD antigen, the antigen is taken up into the B cell
mediated endocytosis, degraded, and presented to T cells as peptide pieces in
with MHC-II molecules on the cell membrane.T helper (TH) cells, typically follicular T
helper (TFH) cells recognize and bind these MHC-II-peptide complexes through their T
cell receptor (TCR).

Now activated, B cells participate in a two-step differentiation process that yields both
short-lived plasmablasts for immediate protection and long-lived plasma cells and memory
B cells for persistent protection. The first step, known as the extrafollicular response, occurs
outside lymphoid follicles but still in the SLO.During this step activated B cells proliferate,
may undergo immunoglobulin class switching, and differentiate into plasmablasts that
produce early, weak antibodies mostly of class IgM.
The second step consists of activated B cells entering a lymphoid follicle and forming
a germinal center (GC), which is a specialized microenvironment where B cells undergo
extensive proliferation.These processes are facilitated by TFH cells within the GC and
generate both high-affinity memory B cells and long-lived plasma cells.
Resultant plasma cells secrete large amounts of antibody and either stay within the SLO or,
more preferentially, migrate to bone marrow.

Natural killing cells
Natural killer cells (also known as NK cells, K cells, and killer cells)
are a type of lymphocyte (a white blood cell) and a component of
innate immune system.
NK cells play a major role in the host-rejection of both tumours and
virally infected cells.
NK cells are cytotoxic; small granules in their cytoplasm contain
special proteins such as perforin and proteases known as

NK cells are activated in response to interferons or
macrophage-derived cytokines.
They serve to contain viral infections while the adaptive
immune response is generating antigen-specific
cytotoxic T cells that can clear the infection
Patients deficient in NK cells prove to be highly
susceptible to early phases of herpes virus infection..

How do natural killer cells works?
• All of our cells have specific set of protiens on their surface
that identifies them as ‘self’(MHC class I).
• Natural killer cells recognize cells that have too few of the
self proteins on their surface and therefore may be infected.
• When an infected cells is recognized,the natural cell releases
a mixture of protiens that enter infectd cell and lead to cell
death(apoptosis).

Dendritic Cells
Dendritic cells (DCs) are antigen-presenting cells (also known as
accessory cells) of the mammalian immune system.
Their main function is to process antigen material and present it on
the cell surface to the T cells of the immune system.
They act as messengers between the innate and the adaptive immune
systems.

Functions of dendritic cells
Maintain immune memory in tandem with B cells.
Antigen presentation and activation of T-cells.
Inducing and maintaining immune tolerance.
To process antigen material and present it on to T-
cells,thus functioning as antigen-presenting cells.

MONOCYTES AND MACROPHAGES
A monocyte is a type of white blood cell and
a type of phagocyte.
A type of immune cell that is made in the
bone marrow and travels through the blood
to tissues in the body where it becomes a
macrophage.
Macrophages surround and kill
microorganisms, ingest foreign material,
remove dead cells, and boost immune
responses

FUNCTIONS OF MONOCYTESMonocytes and their macrophage and dendritic
cell progeny serve three main functions in the
immune system. These are phagocytosis, antigen
presentation, and cytokine production.
Phagocytosis is the process of uptake of microbes
and particles followed by digestion and
destruction of this material.Monocytes can perform phagocytosis using
intermediary proteins such
as antibodies or complement that coat the
pathogen, as well as by binding to the microbe
directly via pattern-recognition receptors that
recognize pathogens.Monocytes are also capable of killing infected host
cells via antibody-dependent cell-mediated
cytotoxicity.

FUNCTIONS OF MACROPHAGES
They assume a defensive role exhibited by
their ability to carry on phagocytosis of
parasites and microbes.
They regulate lymphocyte activation and
proliferation and they are essential in the
activation process of T- and B-lymphocytes
by antigens and allogenic cells.
The removal of dying cells is, to a greater
extent, handled by fixed macrophages

CONCLUSION
• The immune system is a complex array of cells and molecules(such as, T-cells,B-
cells,Dendritic cells,Monocytes,Macrophages,etc) operating in order to protect the host
from pathogenic microorganisms and exogenous noxious agents within our environment.
However, destruction of host tissue may occur if the immune response is inadequate due to
intrinsic or extrinsic mechanisms in cell function, or if there is a hyper-responsiveness due to
dysfunctional regulatory mechanisms. The pathogenesis of periodontal disease is clearly of
an inflammatory origin and, as such, has a close association with the Immune System.

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CELLS THAT DRIVE IMMUNE DEFENSE

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