Download lymphocytes

Lymphocytes
Objectives
Describe the structure and mode of
action of T lymphocytes and B
lymphocytes including the significance
of cell signalling and the role of
memory cells.
Lymphocytes
LYMPHOCYTES are WBC that accumulate in
the lymph and lymph nodes, but are also
found in the spleen and blood. They activate
the immune response
Lymphocytes are mostly
small and inactive cells prior
to infection.
Lymphocytes
Originate from stem cells in the
bone marrow
Small white cells with little
cytoplasm and spherical nuclei
Two types:
1. T cells
2. B cells
Lymphocytes
• B-cells mature in bone marrow then
concentrate in lymph nodes and spleen
• T-cells mature in the thymus
• B and T cells mature then circulate in
the blood and lymph
• Circulation ensures they come into
contact with pathogens and each other
• Lymphocytes are activated by the
presence of an antigen
• Macrophages engulf and break up
pathogens
• They present the antigen on their
surface (APC) for the lymphocytes to
identify
• Macrophages release chemicals called
monokines (a type of cytokine) to
attract neutrophils and activate
lymphocytes
T -Lymphocytes
• Mature T-cells have T cell
receptors which are complementary
to 1 antigen
• They are activated when the
receptor comes into contact with
the Ag on another cell (e.g. an APC
or an invaded body cell)
T-Lymphocytes
Once activated by a specific
antigen (clonal selection) they
divide by mitosis to provide clones
(clonal expansion)
There are 4 main types of T cells:
Helper/Killer/memory/supressor
T-Lymphocytes
T-helper cells – secrete CYTOKINES
 help B cells divide
 stimulate phagocytes
Cytotoxic T cells (killer T cells)
 Kill body cells displaying antigen
Memory T cells
 remain in body for reexposure to
the Ag
The T Cell response is
called the “cell mediated
immune response”
B -Lymphocytes
• There are small group of clones of
B-lymphocytes each of which
produce a specific Ab
• The specific Ab are embedded in
the cell surface membrane and
are called Ab receptors.
B -Lymphocytes
• When the receptors in the
membrane recognise an antigen on
the surface of the pathogen or APC
(clonal selection) that B-cell line
divides rapidly – clonal expansion
• Activation is aided by T helper cells
B -Lymphocytes
• Some activated B cells  PLASMA
CELLS these produce lots of Ab
• The Ab travel to the blood, lymph,
lining of gut and lungs.
• Number of plasma cells decreases
after a few weeks
• Ab stay in the blood longer but
eventually their numbers go down
too.
B-Lymphocytes
• Some activated B cells  MEMORY
CELLS.
• Memory cells divide rapidly as soon as
the antigen is reintroduced.
• When the pathogen infects again it is
destroyed before any symptoms show
The production of Ab by B
cells is called the “humoral
immune” response
B Cells
Clonal
selection
Clonal expansion
antibodies
Summary of the Immune Responses