Organ and tissues of immune system

Immunology Lecture 4th
Organs & Tissues of
Immune system
BY
Dr. Humera Kausar
23rd
Sep 2014

Leucocytes and erythrocytes are derived from bone
marrow stem cells. Lymphocytes, the dominant cells of
immune system mature in the bone marrow (B-
lymphocytes) and Thymus (T-lymphocytes),Hence these
are called primary lymphoid organ or generative
lymphoid organ.
1) Bone Marrow
2) Thymus
Primary lymphoid organ

 BM is the Largest tissue of a mammalian body.
 An adult contain 3kg of bone marrow.
 BM has two distinct kind red and yellow marrow
Primary lymphoid organ
Bone Marrow

Flat, bilobed organ situated above the heart.
function of thymus is to generate & select a
repertoire of T-Cells.
 Each lobe is surrounded by a capsule and
divided in to lobules, which is separated by
strands of connective tissues called trabeculae.
THYMU
S Cortical Epithelial
Cells
Medullary Epithelial Cells
Macrophages
Dendritic Cells
Thymocytes

Cortex and medulla is crisscrossed by 3-
dimensional network of stromal cells composed
of epithelial cells, dendritic cells and
macrophages.
 Many of these stromal cells interact physically
with developing thymocytes.
THYMU
S

 Thymic epithelial cells secrete several hormonal
factors necessary for the differentiation &
maturation of T-Cells.
 As thymocyte develop, an enormous diversity of
T cell receptor is generated by a series of gene
rearrangement.
THYMU
S

 Thymus induces apoptosis of those T-cells that
fails to recognize MHC complexes or react with
MHC complexes.
 More than 95% of thymocytes die by apoptosis
in the thymus.
THYMU
S

Thymic
function
is
known
to
decline
with age
Thymic
Function

Secondary lymphoid organ
are the sites where mature
lymphocytes respond or interact to
foreign antigens that Includes
1.lymph nodes
2.spleen
3.Lymphoid tissues

LYMPH & LYMPHATICS
•Lymph is a clear body
fluid which clots like
blood.
•Lymph forms when
dissolved proteins and
solutes filter out of
venules and capillaries.
(due to hydrostatic &
osmotic pressure)

Thoracic
duct
Overview of blood and lymph system and how
leukocytes travel from one system to another
Site of exchange between the
blood and lymph systems
Lymph carrying antibodies
and immune cells collect in
thoracic duct where the
lymph empties back into the
blood circulatory system

•Lymph flows uni directionally towards lymph
nodes.
• Efferent lymph from regional lymph nodes
may drain into one or more additional nodes
before flowing into major efferent lymphatic.
• Thoracic duct carries lymph draining from
the gut and lower half of the body.
•Lymphatic system is "garbage collector”
LYMPH & LYMPHATICS

1) Lymph nodes
are small nodular
aggregates of lymphoid
tissue situated along
lymphatic channels
throughout the body

LYMPH
NODE
Lymphnodes are bean shaped connective tissue
bags, filled with mobile cell (lymphocyte,
macrophages, dendritic cells) organized in
functional compartments.
Trap Ag & Cells containing Ag.
 Provide a site for clonal expansion.
Cortex
(B-cells,
macrophages,
follicular DC)
Paracortex
(T-cells, DC)
Medulla (sparsely populated lymphoid
cells, many plasma cells)

LYMPH
NODE
 Posses distinct regions of T-cell and B-cell activity and
are surrounded by a fibrous capsule.
 Follicular dendritic cells, of the germinal center, trap
Ag-Ab complexes on membrane for long time.
 Antigenic stimulation in node can increase the no. of
lymphocytes 10-50 fold, resulting in visible swelling of
the node.

LYMPHOID FOLLICLE
Primary follicles (comprises a net work of
follicular dendritic cells & resting B-cells)
 Secondary follicles (a ring of concentrically
packed B lymphocytes surrounding a germinal
center).

SPLEE
N
The spleen is an organ found in virtually all
vertebrates. Similar in structure to a large
lymph node, it acts primarily as a blood filter.

Functions of spleen
 The site of immunocytes residence.
 The site of immune response.
 Produce some active
substances,such as complement,et
al.
 Function of filtration.

SPLEEN PLAYS A
MAJOR ROLE IN
MOUNTING IMMUNE
RESPONSES TO
ANTIGENS IN BLOOD
LYMPHNODES ARE
SPECIALIZED FOR
TRAPPING ANTIGENS
FROM LOCAL TISSUES

Spleen is surrounded by a capsule from which a
number of projections extend in to the interior to form a
compartmentalization.
 Red zone & White zone are separated by marginal
zones.
 Red pulp populated by macrophages, numerous RBC,s
and few lymphocytes.
 Red pulp is the site where old & defective red cells are
destroyed & removed.
SPLEE
N

Splenic white pulp
surrounds the
branches of splenic
artery, forming a
Periarteriolar
lymphoid sheath
(PALS).
SPLEE
N

PALS rich in T cells.
 Marginal zones rich
in B cells & Dendritic
cells.
SPLEE
N

 PALS rich in T
cells.
 Primary
lymphoid follicles
are attached to
the PALS.
 These follicles
are rich in B cells
& some contains
germinal centers.
SPLEEN

 Marginal zones,
peripheral to the
PALS are
populate by
lymphocytes and
macrophages.
SPLEEN

 Blood born Ag. &
lymphocytes enter the
spleen through splenic
artery, empty in to
marginal zone.
 Ag trapped by DC, carry
it to the PALS.
 Blood lymphocytes also
migrate from marginal
zone to the PALS.
SPLEEN

 Initial activation of T & B
cells takes place in the T-
cell rich PALS.
 Activation of
DC T helper B-cell
 Activated B cells with Th
Cells migrate to primary
follicles in marginal zone.
SPLEEN

 On antigenic challenge,
primary follicles
develop into
characteristic secondary
follicles containing
germinal centers.
 Where rapidly dividing
B cells & plasma cells
are surrounded by
dense cluster of
lymphocytes.
SPLEEN

Lymphoid tissues
 Besides the secondary lymphoid organ,
there are some structures which consist
of aggregates of lymphocytes,
macrophages, and other accessory cells.
All such anatomically well defined
structures are collectively called mucosa
-associated lymphoid tissues.(MALT).
 They contain aggregates of immune
cells

MALT
GALT
BALT
 Surface area 400 m2
 Having lose clusters of
lymphoid cells (B-cells,
T cells, macrophages)
 Population of Plasma
cells in MALT is far
exceeds that of in spleen,
lymph nodes & bone
marrow combined.

MALT includes,
Peyer’s patches
Tonsils
Appendix
PEYER’S PATCHES
Peyer's patches (or aggregated lymphoid
nodules) are organized lymphoid tissues,
named after the Swiss anatomist Johann
Peyer. They are aggregations of lymphoid
tissue that are usually found in the lowest
portion of the small intestine, the ileum, in
humans.

PEYER’S PATCHES
Payer,s patches found
within the intestinal
lining, contains well
organized follicles from
which germinal centers
developed upon antigenic
stimulation.
Germinal Centres
M
Cells
Lymphocyte
s

 Tonsils play a role in defense against antigens
entering through the nasal and oral epithelial routes.
 Nodular structure consisting of a meshwork of
reticular cells and fibers interspersed with
lymphocytes, macrophages, granulocytes and mast cells.
 B-cell are organized in to follicles and germinal
centers.
 Germinal centers are surrounded by regions showing
T-cell activity.
TONSILS

Organ and tissues of immune system

Organ and tissues of immune system

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Organ and tissues of immune system