Transcript Power Point

Topics
• The Lymphocytes: B and T cells
• Antigen-specific Receptors on B and T
cells
• CD4+ and CD8+ T cells
• Cytokines
• Antibody production: B cells and Plasma
cells
• Immunological memory
The Lymphocyte
Lymphocytes are mononuclear white blood cells that
perform immunological functions and are
constituents of the adaptive immune response
Small Medium and Large (7 to 15 microns
diameter)
Two types of Lymphocytes:
B (Bone marrow-derived)
T (Thymus-derived)
B and T cells have similar size and morphology
but perform completely different functions
The Lymphocytes Fig 1
The Lymphocyte Fig 2
Antigen Specific Receptors
Both B and T cells have on their surface cellbound molecules that recognize and bind specific
antigen.
These molecules are called Antigen-specific
receptors.
B cell receptors (BCR),
T cell receptors TCR.
Each lymphocyte has many receptor molecules
but all are identical on any given lymphocyte.
Each lymphocyte will recognize and bind only one
Ag specificity
Antigen specific Receptors Fig 3
Many lymphocytes, each
expressing only one type of Agspecific receptor
When the lymphocyte
encounters its specific Ag, the
lymphocyte divides (proliferates)
and gives rise to many more
lymphocytes expressing the
same Ag-specific receptor on
their surface (clone)
Distinctions between B and T lymphocytes
• B cells start and end their development in the
bone marrow
• T cell progenitors migrate from the bone
marrow to the thymus where they develop as
T cells under the influence of the thymic
microenvironment.
• B cells synthesize antibodies.
• T cells do not produce antibodies but have
other multiple functions
T cell types and functions
There are two main classes of T cells:
They are distinguished by the CD (cluster of
differentiation) molecules they express on the
surface: CD4 or CD8
CD4 T cells are called T helper (Th) cells
CD8 T cells are called Cytotoxic T lymphocytes
(CTL)
CD4+ and CD8+ T lymphocytes
CD4 T (Th) cells:
Help B cells to produce antibodies
Participate in inflammatory reactions
Enhance phagocytic activity of monocytes and
macrophages
CD8 T cells (CTL):
Kill virus-infected cells and cells of foreign tissues
and organ transplants by direct cell-to-cell contact
Clonal expansion: T cells
Upon encounter with Ag T cells proliferate and become
effector cells.
Effector T cells produce powerful pharmacologic
mediators called Cytokines.
Cytokines affect the function of other cells as well as
their own
CD4 T cells produce Interleukins (IL-2, IL-4, IL-6, IL-10
etc), Interferon-gamma (IFN-g), Tumor Necrosis Factor,
etc.
CD8 T cells release cytotoxic molecules called perforins
and granzymes which kill the target cells with which the
CTL enters in close contact.
CTL/Target cell interactions Fig 4
a) Viral particles on
infected cell surface
T
b) Influenza-infected
target cell (V) is killed
by CTLs (T)
T
T
CTL Fig 5
Clonal expansion: B cells
As a result of contact with specific Ag, the B lymphocytes
divide (proliferate) and give rise to many more B cells
expressing the same Ag-specific receptor on their surface
and producing the same specific soluble Ab.
B cells synthesize Ab and differentiate into plasma cells
Plasma cells synthesize and secrete Ab. Each B cell clone
produces only one type of Ab specificity.
Antigen specific Receptors Fig 3
Efector cells
produce Ab
The Adaptive immune response has Memory
Encounter of a lymphocyte with its specific Ag gives rise to
effector cells
Effector cells have a limited life-span, and most cells die. The
cells that persist after the Ag has disappeared are called
memory cells and form the basis of immunological memory.
A second encounter with the same Ag will result in a more
rapid response  long-lasting protection.
Memory Contd.
The Ab and T cell responses of an individual to the
first encounter with a specific Ag is called primary
response: slow and weak.
The response to subsequent immunization with the
same Ag (booster immunization), results in stronger
and sustained Ab production and T cell responses
called secondary or anamnestic response
The Secondary Ab response Fig 6
END