Immunology / Organs of immune system and its functions

1. ORGANS
OF
IMMUNE
SYSTEM MARIAM NOORU

2. • Lymphoid organs are the part of the lymphatic system
that are directly involved in the immune system
• They also play a very important role in the development
of immune cells and also act as the checkpoints of
foreign substances.
The lymphoid organs are broadly classified based on their
function
• PRIMARY or CENTRAL LYMPHOID ORGANS
• SECONDARY or PERIPHERAL LYMPHOID ORGANS
LYMPHOID ORGANS

3. • Primary lymphoid organs are those
organs where B and T-lymphocytes
develop, proliferate, mature, acquire
antigen-specific receptors and
become immunocompetent cells.
• After the maturation of lymphocytes,
they migrate to the secondary
lymphoid organs.
• Primary lymphoid organs include
bone marrow and thymus (and the
bursa of Fabricius in birds).
PRIMARY LYMPHOID ORGANS

4. • It is a sponge-like tissue found inside bones.
• It is the main lymphoid organ where all blood cells,
including lymphocytes, are produced and multiply.
• Bone marrow is primarily responsible for both the creation
of T-cell precursors and the production and maturation of
B cells.
• Maturation of B-lymphocytes completes in the bone marrow
only. On the contrary, T-cells travel from the bone marrow to
thethymus, wheretheydevelop furtherandmature.
• From the bone marrow, B cells immediately join the
circulatory system andtraveltosecondarylymphoid organs
• In birds B cells mature in the bursaofFabricius
BONE MARROW

5. • It is a bilobed gland, Situated above heart in the thorax
region
• Each lobe is encapsulated, and it is divided into lobules
which are separated by trabeculae
• Each lobule contains - 1. Outer cortex, 2. Inner medulla
• The cortex contains mostly immature T lymphocytes
(Thymocytes)
• Medulla is sparsely populated with thymocytes.
• Besides lymphoid cells it is composed of
THYMU
S
1. Epithelial cells (cortical and medullary)
2. Macrophages
3. Interdigitating Dendritic cells
4. Nurse cells
5. Hassall’s corpuscles.

6. • Precursor cells (T cells) from the bone marrow
migrate into the outer cortex where they
proliferate. As they mature, about 98% die. This
is known as thymic selection in which T cells that
recognize and bind strongly to the self antigens
are destroyed.
• The remaining 2% move to medulla of thymus,
become mature T cells
and subsequently enter the blood stream.
• Thymus secretes a family of hormones
collectively known as thymosin which is
essential for the normal functioning of the
immune system.

7. • Secondary lymphoid organs are the sites
where B and T-lymphocytes interacts with the
antigens and become effector cells. They are
also called the peripheral lymphoid organs.
• Antibody production from activated B cells
and activation of Tc cells takes place
• These organs include
• lymph nodes
• spleen
• Mucosal associated
lymphoid tissues (MALT)
SECONDARY LYMPHOID ORGANS

8. • Encapsulated bean shaped structures containing a reticular
network
packed with lymphocytes, macrophages and dendritic cells
• A lymph node consists of three regions: the cortex, the
paracortex, and the medulla.
LYMPH
NODES

9. Antigen reaches regional node (lymph)
↓
It is trapped and presented together with Class II MHC
molecules – Antigen ( interdigitating dendritic cells)
↓
Activation of TH cells.
↓
Activation of B cells.
↓
B cells differentiate into memory cells and antibodies
• Each lymph node has a number of lymph vessels called afferent lymphatic vessels, which
pierce the capsule of a lymph node at numerous sites and empty lymph into the sub-
capsular sinus. The lymph now percolates slowly inward through the cortex, paracortex, and
medulla, allowing phagocytic cells and dendritic cells to trap pathogens and antigens
carried by the lymph.
• The lymph then is drained into a single large lymph vessel called efferent lymphatic vessel

10. • It is a large bean-shaped organ located in the left upper
abdomen and beneath the diaphragm.
• Spleen is encapsulated that extends a number of projections,
called trabeculae, into the interior resulting in the formation of
compartments.
• These compartments are consisting of two types of tissues, the
red pulp and white pulp, which are separated by a diffuse
marginal zone.
• The red pulp consists of a network of sinusoids populated by
large number of erythrocytes (red blood cells) and
macrophages and few lymphocytes.
• In fact, red pulp is the region where old and defective
erythrocytes are destroyed and eliminated.
• The white pulp consists of the branches of the splenic artery
that make a periarteriolar lymphoid sheath (PALS) populated
heavily by T-lymphocytes.
SPLEE
N

11. Blood born antigens and lymphocytes enter the spleen through splenic artery
⬇
This empty into marginal zone.
⬇
In marginal zone, Ag trapped by dendritic cells, carry it to PALS.
⬇
In PALS, Initial activation of B and T cells occur.
⬇
Which move to Primary follicle in marginal zone to give rise to Secondary follicle.
• Periarteriolar lymphoid sheath (PALS) is attached with primary lymphoid follicles that are rich in B-lymphocytes.
• The marginal zone separating the red pulp from white pulp is populated by lymphocytes and macrophages.

12. • MALTs are concentrations of many lymphoid tissues found in the various submucosal
membrane sites of the body, like the gastrointestinal tract, nasopharynx, thyroid, breast,
lung, salivary glands, eye, and skin.
• It constitutes about 50% of the lymphoid tissues in the human body.
• They do not serve as the filters of lymph but are the centres of lymphocyte production.
• Apart from B-lymphocytes and T-lymphocytes, phagocytic macrophages and dendritic
cells are also present
• MALT is called by different names depending upon the region they present in.
- Gut-associated lymphoid tissues (GALT)
- Bronchus -associated lymphoid tissues (BALT)
- Cutaneous-associated lymphoid tissues (CALT)
Mucosal-Associated Lymphoid Tissue (MALT)

13. • Tonsils are collections of Lymphoid tissue facing into the Aerodigestive tract.
• The Tonsils play a role in protecting the body against Respiratory infections.
• There are different types of tonsils like palatine tonsils, adenoids, and the lingual tonsil.
• The tonsils contain B lymphocytes and T lymphocytes
• The tonsils defend against antigens entering through the nasal and oral epithelial
routes
• Tonsillitis occurs when bacterial or viral organisms cause inflammation of the Tonsillar
tissue.
• Peyer’s patches are small masses of lymphatic tissue found throughout the Ileum
region of the small intestine.
• These are an important part of gut associated lymphoid tissue (GALT).
• In Payer's patch antigen is collected by specialized epithelial cells called M cells
• T cells, B-cells and memory cells are stimulated when antigens come in contact
with Peyer’s patches.
• They play an important role in the immune system by monitoring the intestinal
bacteria populations.
PAYER'S PATCHES
TONSI
L