Anatomy and Components of
Immune System
2011
Components of Immune system
Immune System-Anatomy
• The bone marrow hemopoietic stem cells are
the ultimate origin of :
 erythrocytes
 all leucocytes including the lymphocytes.
• Many lymphocytes pass through the thymus
when they become processed by humoral
microenvironment prior to release.
• These lymphocytes are now called thymusderived lymphocytes, T-lymphocytes or Tcells.
• The majority of the bone marrow derived
lymphocytes which do not enter or become
processed by the thymus are called B-cells.
Formation of B-cells and T cells
Cells of the Immune system
Many cells of the immune system derived from the
bone marrow, Hematopoetic stem cell differentiation
Cells of the Immune system
Lymphocytes
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Lymphocytes are mononuclear, non granular.
Found in blood, spleen, lymph node, tonsil.
They are spherical or ovoid in shape.
They arise from pluripotential haemopoietic stem
cells.
• They are important in both humoral and cellmediated immunity
• Types of lymphocytes:
1. B lymphocytes
2. T lymphocytes
3. Null cells
B lymphocytes /B cells
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Mature in bone marrow
Are mononuclear and non granular
Have a large nucleus
Found in blood and lymph
Highly concentrated in lymph nodes and spleen.
Contain immunoglobulin on their surfaces.
Immature B cells changes to mature B cells which
has IgD and IgM.
• B-cells produce antibodies brings about humoral
immunity
Protection by B cells
• When bacteria, virus and toxins stimulate B cells,
• B cells divide rapidly and forms two types of cells
1.
Plasma cells- secrete antibodies in response
to specific antigens- Primary response
2.
B memory cells
• move from blood to lymph
• Survive for longer time
• respond quickly and effectively during similar
subsequent infection
• Produce antibodies - secondary
response
T Lymphocytes/ T- cells
• Derived from haemopoietic stem cells of bone marrow
• mononuclear, non-granular leucocytes that matures in
thymus
• They become functional on exposure to antigen
• Brings about cell mediated immunity.
• Types of T cells:
1. T helper cells ( TH cells)
2. T suppressor cells T ( TS cells)
3. T cytotoxic cells ( TC cells)
4. T delayed type hypersensitivity cells ( TD cells)
T helper cells ( TH cells)
• Regulator cells
• T helper cells get activated by very small quantities of
antigens which cannot activate other cells.
• Helper T cells: release interleukin-2 which in turn
triggers the release of other cytokines.
Cytokines: any soluble factor secreted that act as a
signal to other lymphoid cells. There are two
categories:1. Lymphokines: secreted by lymphocytes
2. Monokines: secreted by macrophages
Certain cytokines like interferon and interleukins are
secreted by both lymphocytes and macrophages
• Lymphokines increase the response of B cells,
T killer cells and T suppressor cells.
• B cells are activated to produce antibodies.
• Another type of Lymphokines secreted by
helper cells called macrophage migration
inhibition
factors
which
cause
the
accumulation of macrophages around the
antigen and activation of macrophages to
perform phagocytosis.
T Suppressor Cells (TS cells)
• Suppress the activity of B cells and other T
cells.
• Are the regulatory T cells.
• They inhibit antibody production by B cells.
• They suppress the function of the T killer and
T helper cells.
• Suppressor T cells are responsible for immune
tolerance by limiting the ability of the immune
system to attack a person’s own body tissues.
Cytotoxic T cells ( Tc) or T killer cells (Tk)
– recognizes the foreign antigen on the surface
of virus infected cells and destroy the cells
releasing cytolytic protein.
– Cytotoxic substances are probably lysosomal
enzymes manufactured in the Tc cells.
– Cytotoxic T cells (Tc) are lethal to tissue cells
that have been invaded by viruses.
– The virus particles entrapped in membranes of
infected cells attract T cells because of viral
antigenicity and Tc cells ultimately damage the
virus infected tissue cells.
• Also play important role in destroying cancer
cells, heart transplant cells or other types of
cells that are foreign to the persons own body.
T Delayed Type Hypersensitivity cells (TD)
• Brings macrophages to areas where delayed
hypersensitivity reaction occur.
• TD similar to TH cells.
• TD secrete primarily macrophage chemotoxin
and macrophage migration inhibition factor.
• By secreting these lymphokines the TD cells
are directly involved in the delayed
hypersensitivity reaction.
Plasma Cell
– Fully differentiated B cells.
– Do not divide and have a half life of about
2-4 days.
– Found rarely in plasma of blood but are
found in lymph nodes and spleen.
– secretes Antibodies (immunoglobulins)
Null Cells
• Are lymphocytes with cytotoxic properties.
• Neither B cells nor T cells but intermediate.
• Two kinds:
1. Natural Killer cells and
2. Killer cells
Natural Killer cells
– Have 2 or 3 large granules in the cytoplasm
– Have kidney shaped nucleus
– Kills cells infected with certain viruses
– Kill the target cells without the aid of antibody and
complement - antibody independent.
– Destroy the cancer cells and cells infected with
herpes and mumps virus.
– Don’t need antibody
– Activated by interferon and interleukin
– Both innate and adaptive
Killer cells ( K cells)
• Are antibody dependent.
• Depends on the presence of bound antibody,
• thus reaction is termed- antibody-dependent
cell- mediated cytotoxic reaction.
• K cells can kill a variety of cells such as tumor
cells, bacteria, viruses, fungi and parasites.
Monocytes/Macrophage
• Are large, mononuclear phagocytic
cells derived from monocyte.
• Have large nucleus and contain
a large number of lysosomes
• Strongly phagocytic to a wide
variety of particulate materials such as
microorganisms, dead cells, effete cells, debris,
immune complex.
• Phagocytosis and killing of microorganisms
• Activation of T cells and initiation of
immune response.
• Involved in the processing of antigen before
they are presented to the T and B cells.
Macrophages are important secretary cellssecrete substances such as components of
complement system, hydrolytic enzymes, toxic
forms of oxygen and monokines.
• Monocyte is a young macrophage in blood
Dendritic Cells
• Activation of T cells and initiate adaptive
immunity
• Found mainly in lymphoid tissue
• Function as antigen presenting cells (APC)
• Most potent stimulator of T-cell response
Mast Cells
• Large cells with basophilic granules in the
cytoplasm.
• Mast cells are similar to basophils of the
blood, in appearance and functions.
• Expulsion of parasites through release of
granules.
• Release substances like serotonin, histamine,
heparin, platelet activating factors, leukotrines
and prostaglandins which
brings about
inflammatory and allergic reactions.
Neutrophil
• Granulocyte
– Cytoplasmic granules
• Polymorphonuclear
• Short life span (hours)
• Phagocytosis
• Very important at “clearing” bacterial
infections
• Innate Immunity
Eosinophils
• Double Lobed nucleus
• Granules are rich in hydrolytic
enzymes.
• Kills Ab-coated parasites through
degranulation.
Involved in allergic inflammation
• Orange granules contain toxic compounds
Basophils
• Might be “blood Mast cells’
• A cell-killing cells
• Blue granules contain toxic
and inflammatory compounds.
• Important in allergic reactions.
• The basophilic granules are believed to contain
heparin, histamine, serotonin, platelet activating
factor and other vasoactive amines that may be
released at the sire of inflammation or region of
immediate hypersensitivity reaction.
Other Blood Cells
• Megakaryocyte
– Platelet formation
– Wound repair
– Involved in immune response, especially in
inflammation.
– Involved in hypersensitivity reaction.
• Erythrocyte
– Oxygen transport
Task
• Differentiate between B cell and T cell
END